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L_0931 | isomers | T_4555 | Because isomers are different compounds, they have different properties. Generally, branched-chain isomers have lower boiling and melting points than straight-chain isomers. For example, the boiling and melting points of iso- butane are -12 C and -160 C, respectively, compared with 0 C and -138 C for n-butane. The more branching there is, the lower the boiling and melting points are. Q: The boiling point of n-pentane is 36 C. Predict the boiling points of iso-pentane and neo-pentane. A: The boiling point of iso-pentane is 28 C, and the boiling point of neo-pentane is 10 C. | text | null |
L_0932 | isotopes | T_4556 | All atoms of the same element have the same number of protons, but some may have different numbers of neutrons. For example, all carbon atoms have six protons, and most have six neutrons as well. But some carbon atoms have seven or eight neutrons instead of the usual six. Atoms of the same element that differ in their numbers of neutrons are called isotopes. Many isotopes occur naturally. Usually one or two isotopes of an element are the most stable and common. Different isotopes of an element generally have the same physical and chemical properties. Thats because they have the same numbers of protons and electrons. Click image to the left or use the URL below. URL: | text | null |
L_0932 | isotopes | T_4557 | Hydrogen is an example of an element that has isotopes. Three isotopes of hydrogen are modeled in the Figure hydrogen. Some hydrogen atoms have one neutron as well. These atoms are the isotope named deuterium. Other hydrogen atoms have two neutrons. These atoms are the isotope named tritium. Q: The mass number of an atom is the sum of its protons and neutrons. What is the mass number of each isotope of hydrogen shown above? A: The mass numbers are: hydrogen = 1, deuterium = 2, and tritium = 3. | text | null |
L_0932 | isotopes | T_4558 | For most elements other than hydrogen, isotopes are named for their mass number. For example, carbon atoms with the usual 6 neutrons have a mass number of 12 (6 protons + 6 neutrons = 12), so they are called carbon-12. Carbon atoms with 7 neutrons have an atomic mass of 13 (6 protons + 7 neutrons = 13). These atoms are the isotope called carbon-13. Q: Some carbon atoms have 8 neutrons. What is the name of this isotope of carbon? A: Carbon atoms with 8 neutrons have an atomic mass of 14 (6 protons + 8 neutrons = 14), so this isotope of carbon is named carbon-14. | text | null |
L_0932 | isotopes | T_4559 | Atoms need a certain ratio of neutrons to protons to have a stable nucleus. Having too many or too few neutrons relative to protons results in an unstable, or radioactive, nucleus that will sooner or later break down to a more stable form. This process is called radioactive decay. Many isotopes have radioactive nuclei, and these isotopes are referred to as radioisotopes. When they decay, they release particles that may be harmful. This is why radioactive isotopes are dangerous and why working with them requires special suits for protection. The isotope of carbon known as carbon-14 is an example of a radioisotope. In contrast, the carbon isotopes called carbon-12 and carbon-13 are stable. | text | null |
L_0933 | kinetic energy | T_4560 | Kinetic energy is the energy of moving matter. Anything that is moving has kinetic energyfrom atoms in matter to stars in outer space. Things with kinetic energy can do work. For example, the spinning saw blade in the photo above is doing the work of cutting through a piece of metal. | text | null |
L_0933 | kinetic energy | T_4561 | The amount of kinetic energy in a moving object depends directly on its mass and velocity. An object with greater mass or greater velocity has more kinetic energy. You can calculate the kinetic energy of a moving object with this equation: Kinetic Energy (KE) = 12 mass velocity2 This equation shows that an increase in velocity increases kinetic energy more than an increase in mass. If mass doubles, kinetic energy doubles as well, but if velocity doubles, kinetic energy increases by a factor of four. Thats because velocity is squared in the equation. Lets consider an example. The Figure 1.1 shows Juan running on the beach with his dad. Juan has a mass of 40 kg and is running at a velocity of 1 m/s. How much kinetic energy does he have? Substitute these values for mass and velocity into the equation for kinetic energy: m2 2 KE = 12 40 kg (1 m s ) = 20 kg s2 = 20 N m, or 20 J Notice that the answer is given in joules (J), or N m, which is the SI unit for energy. One joule is the amount of energy needed to apply a force of 1 Newton over a distance of 1 meter. What about Juans dad? His mass is 80 kg, and hes running at the same velocity as Juan (1 m/s). Because his mass is twice as great as Juans, his kinetic energy is twice as great: m2 2 KE = 12 80 kg (1 m s ) = 40 kg s2 = 40 N m, or 40 J Q: What is Juans kinetic energy if he speeds up to 2 m/s from 1 m/s? A: By doubling his velocity, Juan increases his kinetic energy by a factor of four: m2 2 KE = 12 40 kg (2 m s ) = 80 kg s2 = 80 N m, or 80 J | text | null |
L_0934 | kinetic theory of matter | T_4562 | Energy is the ability to cause changes in matter. For example, your body uses chemical energy when you lift your arm or take a step. In both cases, energy is used to move matteryou. Any matter that is moving has energy just because its moving. The energy of moving matter is called kinetic energy. Scientists think that the particles of all matter are in constant motion. In other words, the particles of matter have kinetic energy. The theory that all matter consists of constantly moving particles is called the kinetic theory of matter. | text | null |
L_0934 | kinetic theory of matter | T_4563 | Differences in kinetic energy explain why matter exists in different states. Particles of matter are attracted to each other, so they tend to pull together. The particles can move apart only if they have enough kinetic energy to overcome this force of attraction. Its like a tug of war between opposing sides, with the force of attraction between particles on one side and the kinetic energy of individual particles on the other side. The outcome of the war determines the state of matter. If particles do not have enough kinetic energy to overcome the force of attraction between them, matter exists as a solid. The particles are packed closely together and held rigidly in place. All they can do is vibrate. This explains why solids have a fixed volume and a fixed shape. If particles have enough kinetic energy to partly overcome the force of attraction between them, matter exists as a liquid. The particles can slide past one another but not pull apart completely. This explains why liquids can change shape but have a fixed volume. If particles have enough kinetic energy to completely overcome the force of attraction between them, matter exists as a gas. The particles can pull apart and spread out. This explains why gases have neither a fixed volume nor a fixed shape. Look at the Figure 1.1. It sums up visually the relationship between kinetic energy and state of matter. Q: How could you use a bottle of cola to demonstrate these relationships between kinetic energy and state of matter? A: You could shake a bottle of cola and then open it. Shaking causes carbon dioxide to come out of the cola solution and change to a gas. The gas fizzes out of the bottle and spreads into the surrounding air, showing that its particles have enough kinetic energy to spread apart. Then you could tilt the open bottle and pour out a small amount of the cola on a table, where it will form a puddle. This shows that particles of the liquid have enough kinetic energy to slide over each other but not enough to pull apart completely. If you do nothing to the solid glass of the cola bottle, it will remain the same size and shape. Its particles do not have enough energy to move apart or even to slide over each other. | text | null |
L_0935 | law of conservation of momentum | T_4564 | When skater 2 runs into skater 1, hes going faster than skater 1 so he has more momentum. Momentum is a property of a moving object that makes it hard to stop. Its a product of the objects mass and velocity. At the moment of the collision, skater 2 transfers some of his momentum to skater 1, who shoots forward when skater 2 runs into him. Whenever an action and reaction such as this occur, momentum is transferred from one object to the other. However, the combined momentum of the objects remains the same. In other words, momentum is conserved. This is the law of conservation of momentum. Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL: | text | null |
L_0935 | law of conservation of momentum | T_4565 | The Figure 1.1 shows how momentum is conserved in the two colliding skaters. The total momentum is the same after the collision as it was before. However, after the collision, skater 1 has more momentum and skater 2 has less momentum than before. Q: What if two skaters have a head-on collision? Do you think momentum is conserved then? A: As in all actions and reactions, momentum is also conserved in a head-on collision. | text | null |
L_0936 | law of reflection | T_4566 | Reflection is one of several ways that light can interact with matter. Light reflects off surfaces such as mirrors that do not transmit or absorb light. When light is reflected from a smooth surface, it may form an image. An image is a copy of an object that is formed by reflected (or refracted) light. Q: Is an image an actual object? If not, what is it? A: No, an image isnt an actual object. It is focused rays of light that make a copy of an object, like a picture projected on a screen. | text | null |
L_0936 | law of reflection | T_4567 | If a surface is extremely smooth, as it is in a mirror, then the image formed by reflection is sharp and clear. This is called regular reflection (also called specular reflection). However, if the surface is even slightly rough or bumpy, an image may not form, or if there is an image, it is blurry or fuzzy. This is called diffuse reflection. Q: Look at the boats and their images in the Figure 1.1. Which one represents regular reflection, and which one represents diffuse reflection? A: Reflection of the boat on the left is regular reflection. The water is smooth and the image is sharp and clear. Reflection of the boat on the right is diffuse reflection. The water has ripples and the image is blurry and wavy. In the Figure 1.2, you can see how both types of reflection occur. Waves of light are represented by arrows called rays. Rays that strike the surface are referred to as incident rays, and rays that reflect off the surface are known as reflected rays. In regular reflection, all the rays are reflected in the same direction. This explains why regular reflection forms a clear image. In diffuse reflection, the rays are reflected in many different directions. This is why diffuse reflection forms, at best, a blurry image. | text | null |
L_0936 | law of reflection | T_4567 | If a surface is extremely smooth, as it is in a mirror, then the image formed by reflection is sharp and clear. This is called regular reflection (also called specular reflection). However, if the surface is even slightly rough or bumpy, an image may not form, or if there is an image, it is blurry or fuzzy. This is called diffuse reflection. Q: Look at the boats and their images in the Figure 1.1. Which one represents regular reflection, and which one represents diffuse reflection? A: Reflection of the boat on the left is regular reflection. The water is smooth and the image is sharp and clear. Reflection of the boat on the right is diffuse reflection. The water has ripples and the image is blurry and wavy. In the Figure 1.2, you can see how both types of reflection occur. Waves of light are represented by arrows called rays. Rays that strike the surface are referred to as incident rays, and rays that reflect off the surface are known as reflected rays. In regular reflection, all the rays are reflected in the same direction. This explains why regular reflection forms a clear image. In diffuse reflection, the rays are reflected in many different directions. This is why diffuse reflection forms, at best, a blurry image. | text | null |
L_0936 | law of reflection | T_4568 | One thing is true of both regular and diffuse reflection. The angle at which the reflected rays leave the surface is equal to the angle at which the incident rays strike the surface. This is known as the law of reflection. The law is illustrated in the Figure 1.3. | text | null |
L_0937 | lens | T_4569 | A lens is a transparent object with one or two curved surfaces. It is typically made of glass (or clear plastic in the case of a contact lens). A lens refracts, or bends, light and forms an image. An image is a copy of an objected formed by the refraction (or reflection) of visible light. The more curved the surface of a lens is, the more it refracts the light that passes through it. There are two basic types of lenses: concave and convex. The two types of lenses have different shapes, so they bend light and form images in different ways. | text | null |
L_0937 | lens | T_4570 | A concave lens is thicker at the edges than it is in the middle. You can see the shape of a concave lens in the Figure Note that the image formed by a concave lens is on the same side of the lens as the object. It is also smaller than the object and right-side up. However, it isnt a real image. It is a virtual image. Your brain tricks you into seeing an image there. The light rays actually pass through the glass to the other side and spread out in all directions. | text | null |
L_0937 | lens | T_4571 | A convex lens is thicker in the middle than at the edges. You can see the shape of a convex lens in the Figure 1.2. A convex lens causes rays of light to converge, or meet, at a point called the focus (F). A convex lens forms either a real or virtual image. It depends on how close the object is to the lens relative to the focus. Q: An example of a convex lens is a hand lens. Which of the three convex lens diagrams in the Figure 1.2 shows how a hand lens makes an image? A: Youve probably looked through a hand lens before. If you have, then you know that the image it produces is right-side up. Therefore, the first diagram must show how a hand lens makes an image. Its the only one that produces a right-side up image. | text | null |
L_0938 | lever | T_4572 | A lever is a simple machine consisting of a bar that rotates around a fixed point. The fixed point of a lever is called the fulcrum. Like other machines, a lever makes work easier by changing the force applied to the machine or the distance over which the force is applied. How does a hammer make it easier to pull a nail out of a board? First, it changes the direction of the force applied to the hammerthe hand pushes down on the handle while the claw end of the hammer head pulls up. Often, you can push down with more force than you can push up because you can put your own weight behind it. The hammer also increases the strength of the force that is applied to it. It easily pulls the nail out of the board, which you couldnt do with your hands alone. On the other hand, the hammer decreases the distance over which the force is applied. The hand pushing down on the handle moves the handle over a distance of several inches, whereas the hammer pulls up on the nail only an inch or two. Q: Where is the fulcrum of the hammer when it is used to pull a nail out of a board? In other words, around what point does the hammer rotate? A: The fulcrum is the point where the head of the hammer rests on the surface of the board. | text | null |
L_0938 | lever | T_4573 | Other levers change force or distance in different ways than a hammer removing a nail. How a lever changes force or distance depends on the location of the input and output forces relative to the fulcrum. The input force is the force applied by the user to the lever. The output force is the force applied by the lever to the object. Based on the location of input and output forces, there are three basic types of levers, called first-class, second-class, and third-class levers. The Table 1.1 describes the three classes. Class of Lever Example of Lever in This Class First class Location of Input & Output Forces & Fulcrum* Ideal Mechanical Advantage Change in Direction of Force? Seesaw 1 <1 >1 yes yes yes Second class Wheelbarrow >1 no Third class Hockey stick <1 no = fulcrum I = input force O = output force The Table 1.1 includes the ideal mechanical advantage of each class of lever. The mechanical advantage is the factor by which a machine changes the input force. The ideal mechanical advantage is the increase or decrease in force that would occur if there were no friction to overcome in the use of the machine. Because all machines must overcome some friction, the ideal mechanical advantage is always somewhat greater than the actual mechanical advantage of the machine as it is used in the real world. Q: Which class of lever is a hammer when it is used to pry a nail out of a board? What is its mechanical advantage? A: To pry a nail out of a board, the fulcrum is located between the input and output forces. Therefore, when a hammer is used in this way it is a first class lever. The fulcrum is closer to the output force than the input force, so the mechanical advantage is >1. In other words, the hammer increases the force applied to it, making it easier to pry the nail out of the board. | text | null |
L_0938 | lever | T_4574 | All three classes of levers make work easier, but they do so in different ways. When the input and output forces are on opposite sides of the fulcrum, the lever changes the direction of the applied force. This occurs only with first-class levers. When both the input and output forces are on the same side of the fulcrum, the direction of the applied force does not change. This occurs with both second-class and third-class levers. When the input force is applied farther from the fulcrum than the output force is, the output force is greater than the input force, and the ideal mechanical advantage is greater than 1. This always occurs with second-class levers and may occur with first-class levers. When the input force is applied closer to the fulcrum than the output force is, the output force is less than the input force, and the ideal mechanical advantage is less than 1. This always occurs with third-class levers and may occur with first-class levers. When the input and output forces are the same distance from the fulcrum, the output force equals the input force, and the ideal mechanical advantage is 1. This occurs only with first some first-class levers. | text | null |
L_0938 | lever | T_4575 | You may be wondering why you would use a third-class lever when it doesnt change the direction or strength of the applied force. The advantage of a third-class lever is that the output force is applied over a greater distance than the input force. The output end of the lever must move faster than the input end in order to cover the greater distance. Q: A broom is a third-class lever when it is used to sweep a floor (see the Figure 1.1), so the output end of the lever moves faster than the input end. Why is this useful? A: By moving more quickly over the floor, the broom does the work faster. | text | null |
L_0939 | light | T_4576 | Electromagnetic waves are waves that carry energy through matter or space as vibrating electric and magnetic fields. Electromagnetic waves have a wide range of wavelengths and frequencies. Sunlight contains the complete range of wavelengths of electromagnetic waves, which is called the electromagnetic spectrum. The Figure 1.1 shows all the waves in the spectrum. | text | null |
L_0939 | light | T_4577 | Light includes infrared light, visible light, and ultraviolet light. As you can see from the Figure 1.1, light falls roughly in the middle of the electromagnetic spectrum. It has shorter wavelengths and higher frequencies than microwaves, but not as short and high as X rays. Q: Which type of light do you think is harmful to the skin? A: Waves of light with the highest frequencies have the most energy and are harmful to the skin. Use the electro- magnetic spectrum in the Figure 1.1 to find out which of the three types of light have the highest frequencies. | text | null |
L_0939 | light | T_4578 | Light with the longest wavelengths is called infrared light. The term infrared means below red. Infrared light is the range of light waves that have longer wavelengths and lower frequencies than red light in the visible range of light waves. The sun gives off infrared light as do flames and living things. You cant see infrared light waves, but you can feel them as heat. But infrared cameras and night vision goggles can detect infrared light waves and convert them to visible images. | text | null |
L_0939 | light | T_4579 | The only light that people can see is called visible light. This light consists of a very narrow range of wavelengths that falls between infrared light and ultraviolet light. Within the visible range, we see light of different wavelengths as different colors of light, from red light, which has the longest wavelength, to violet light, which has the shortest wavelength (see Figure 1.2). When all of the wavelengths of visible light are combined, as they are in sunlight, visible light appears white. | text | null |
L_0939 | light | T_4580 | Light with wavelengths shorter than visible light is called ultraviolet light. The term ultraviolet means above violet. Ultraviolet light is the range of light waves that have shorter wavelengths and higher frequencies than violet light in the visible range of light. With higher frequencies than visible light, ultraviolet light has more energy. It can be used to kill bacteria in food and to sterilize surgical instruments. The human skin also makes vitamin D when it is exposed to ultraviolet light. Vitamin D, in turn, is needed for strong bones and teeth. Too much exposure to ultraviolet light can cause sunburn and skin cancer. As the slip, slop, slap slogan suggests, you can protect your skin from ultraviolet light by wearing clothing that covers your skin, applying sunscreen to any exposed areas, and wearing a hat to protect your head from exposure. The SPF, or sun-protection factor, of sunscreen gives a rough idea of how long it protects the skin from sunburn (see Figure 1.3). A sunscreen with a higher SPF value protects the skin longer. Sunscreen must be applied liberally and often to be effective, and no sunscreen is completely waterproof. Q: You should apply sunscreen even on cloudy days. Can you explain why? A: Ultraviolet light can travel through clouds, so it can harm unprotected skin even on cloudy days. | text | null |
L_0940 | lipid classification | T_4581 | Lipids are one of four classes of biochemical compounds, which are compounds that make up living things and carry out life processes. (The other three classes of biochemical compounds are carbohydrates, proteins, and nucleic acids.) Living things use lipids to store energy. Lipids are also the major components of cell membranes in living things. Types of lipids include fats and oils. Fats are solid lipids that animals use to store energy. Oils are liquid lipids that plants use to store energy. Q: Can you name some lipids that are fats? What are some lipids that are oils? A: Lipids that are fats include butter and the fats in meats. Lipids that are oils include olive oil and vegetable oil. Examples of both types of lipids are pictured in the Figure 1.1. | text | null |
L_0940 | lipid classification | T_4582 | Lipids consist only or mainly of carbon, hydrogen, and oxygen. Both fats and oils are made up of long chains of carbon atoms that are bonded together. These chains are called fatty acids. Fatty acids may be saturated or (A) The white bands on these lamb chops are fat. (B) The yellow liquid in this bottle is olive oil. unsaturated. In the Figure 1.2 you can see structural formulas for two small fatty acids, one saturated and one unsaturated. Saturated fatty acids have only single bonds between carbon atoms. As a result, the carbon atoms are bonded to as many hydrogen atoms as possible. In other words, the carbon atoms are saturated with hydrogens. Saturated fatty acids are found in fats. Unsaturated fatty acids have at least one double bond between carbon atoms. As a result, some carbon atoms are not bonded to as many hydrogen atoms as possible. They are unsaturated with hydrogens. Unsaturated fatty acids are found in oils. Q: Both of these fatty acid molecules have six carbon atoms and two oxygen atoms. How many hydrogen atoms does each fatty acid molecule contain? What else is different about the two molecules? A: The saturated fatty acid molecule has 12 hydrogen atoms. This is as many hydrogen atoms as can possibly be bonded to carbon atoms in this molecule. The unsaturated fatty acid molecule has 10 hydrogen atoms, or two less than the maximum possible number. The saturated fatty acid has only single bonds between its carbon atoms. The unsaturated fatty acid has a double bond between two of its carbon atoms. | text | null |
L_0940 | lipid classification | T_4582 | Lipids consist only or mainly of carbon, hydrogen, and oxygen. Both fats and oils are made up of long chains of carbon atoms that are bonded together. These chains are called fatty acids. Fatty acids may be saturated or (A) The white bands on these lamb chops are fat. (B) The yellow liquid in this bottle is olive oil. unsaturated. In the Figure 1.2 you can see structural formulas for two small fatty acids, one saturated and one unsaturated. Saturated fatty acids have only single bonds between carbon atoms. As a result, the carbon atoms are bonded to as many hydrogen atoms as possible. In other words, the carbon atoms are saturated with hydrogens. Saturated fatty acids are found in fats. Unsaturated fatty acids have at least one double bond between carbon atoms. As a result, some carbon atoms are not bonded to as many hydrogen atoms as possible. They are unsaturated with hydrogens. Unsaturated fatty acids are found in oils. Q: Both of these fatty acid molecules have six carbon atoms and two oxygen atoms. How many hydrogen atoms does each fatty acid molecule contain? What else is different about the two molecules? A: The saturated fatty acid molecule has 12 hydrogen atoms. This is as many hydrogen atoms as can possibly be bonded to carbon atoms in this molecule. The unsaturated fatty acid molecule has 10 hydrogen atoms, or two less than the maximum possible number. The saturated fatty acid has only single bonds between its carbon atoms. The unsaturated fatty acid has a double bond between two of its carbon atoms. | text | null |
L_0940 | lipid classification | T_4583 | Some lipids contain the element phosphorus as well as carbon, hydrogen, and oxygen. These lipids are called phospholipids. Two layers of phospholipid molecules make up the cell membranes of living things. In the Figure One end of each phospholipid molecule is polar, so it has a partial electric charge. Water is also polar and has electrically charged ends, so it is attracted to the oppositely charged end of a phospholipid molecule. This end of the phospholipid molecule is described as hydrophilic, which means water loving. The other end of each phospholipid molecule is nonpolar and has no electric charge. This end of the phospho- lipid molecule repels polar water and is described as hydrophobic, or water hating. In the Figure 1.3, the hydrophilic ends of the phospholipid molecules are on the outsides of the cell membrane, and the hydrophobic ends are on the inside of the cell membrane. This arrangement of phospholipids allows some substances to pass through the cell membrane while keeping other substances out. | text | null |
L_0942 | longitudinal wave | T_4586 | A longitudinal wave is a type of mechanical wave. A mechanical wave is a wave that travels through matter, called the medium. In a longitudinal wave, particles of the medium vibrate in a direction that is parallel to the direction that the wave travels. You can see this in the Figure 1.1. The persons hand pushes and pulls on one end of the spring. The energy of this disturbance passes through the coils of the spring to the other end. Click image to the left or use the URL below. URL: | text | null |
L_0942 | longitudinal wave | T_4587 | Notice in the Figure 1.1 that the coils of the spring first crowd closer together and then spread farther apart as the wave passes through them. Places where particles of a medium crowd closer together are called compressions, and places where the particles spread farther apart are called rarefactions. The more energy the wave has, the closer together the particles are in compressions and the farther apart they are in rarefactions. | text | null |
L_0942 | longitudinal wave | T_4588 | Earthquakes cause longitudinal waves called P waves. The disturbance that causes an earthquake sends longitudinal waves through underground rocks in all directions away from the disturbance. P waves are modeled in the Figure Q: Where are the compressions and rarefactions of the medium in this model of P waves? A: The compressions are the places where the vertical lines are closest together. The rarefactions are the places where the vertical lines are farthest apart. | text | null |
L_0943 | magnetic field reversal | T_4589 | Earths magnetic poles have switched places repeatedly in the past. As you can see in the Figure 1.1, each time the switch occurred, Earths magnetic field was reversed. The magnetic field is the region around a magnet over which it exerts magnetic force. We think of todays magnetic field direction as normal, but thats only because its what were used to. | text | null |
L_0943 | magnetic field reversal | T_4590 | Scientists dont know for certain why magnetic reversals occur, but there is hard evidence that they have for hundreds of millions of years. The evidence comes from rocks on the ocean floor. Look at Figure 1.2. They show the same ridge on the ocean floor during different periods of time. A. At the center of the ridge, hot magma pushes up through the crust and hardens into rock. Once the magma hardens, the alignment of magnetic domains in the rock is frozen in place forever. Magnetic domains are regions in the rocks where all the atoms are lined up and pointing toward Earths north magnetic pole. B. The newly hardened rock is gradually pushed away from the ridge in both directions as more magma erupts and newer rock forms. The alignment of magnetic domains in this new rock is in the opposite direction, showing that a magnetic reversal has occurred. C. A magnetic reversal occurs again. It is frozen in rock to document the change. Rock samples from many places on the ocean floor show that the north and south magnetic poles reversed hundreds of times over the last 330 million years. The last reversal was less than a million years ago. | text | null |
L_0944 | magnets | T_4591 | A magnet is an object that attracts certain materials such as iron. Youre probably familiar with common bar magnets, like the one shown in the Figure 1.1. Like all magnets, this bar magnet has north and south magnetic poles. The red end of the magnet is the north pole and the blue end is the south pole. The poles are regions where the magnet is strongest. The poles are called north and south because they always line up with Earths north-south axis if the magnet is allowed to move freely. (Earths axis is the imaginary line around which the planet rotates.) Q: What do you suppose would happen if you cut the bar magnet pictured in the Figure 1.1 along the line between the north and south poles? A: Both halves of the magnet would also have north and south poles. If you cut each of the halves in half, all those pieces would have north and south poles as well. Pieces of a magnet always have both north and south poles no matter how many times you cut the magnet. | text | null |
L_0944 | magnets | T_4592 | The force that a magnet exerts on certain materials, including other magnets, is called magnetic force. The force is exerted over a distance and includes forces of attraction and repulsion. North and south poles of two magnets attract each other, while two north poles or two south poles repel each other. A magnet can exert force over a distance because the magnet is surrounded by a magnetic field. In the Figure 1.2, you can see the magnetic field surrounding a bar magnet. Tiny bits of iron, called iron filings, were placed under a sheet of glass. When the magnet was placed on the glass, it attracted the iron filings. The pattern of the iron filings shows the lines of force that make up the magnetic field of the magnet. The concentration of iron filings near the poles indicates that these areas exert the strongest force. You can also see how the magnetic field affects the compasses placed above the magnet. When two magnets are brought close together, their magnetic fields interact. You can see how they interact in the Figure 1.3. The lines of force of north and south poles attract each other whereas those of two north poles repel each other. | text | null |
L_0944 | magnets | T_4592 | The force that a magnet exerts on certain materials, including other magnets, is called magnetic force. The force is exerted over a distance and includes forces of attraction and repulsion. North and south poles of two magnets attract each other, while two north poles or two south poles repel each other. A magnet can exert force over a distance because the magnet is surrounded by a magnetic field. In the Figure 1.2, you can see the magnetic field surrounding a bar magnet. Tiny bits of iron, called iron filings, were placed under a sheet of glass. When the magnet was placed on the glass, it attracted the iron filings. The pattern of the iron filings shows the lines of force that make up the magnetic field of the magnet. The concentration of iron filings near the poles indicates that these areas exert the strongest force. You can also see how the magnetic field affects the compasses placed above the magnet. When two magnets are brought close together, their magnetic fields interact. You can see how they interact in the Figure 1.3. The lines of force of north and south poles attract each other whereas those of two north poles repel each other. | text | null |
L_0944 | magnets | T_4592 | The force that a magnet exerts on certain materials, including other magnets, is called magnetic force. The force is exerted over a distance and includes forces of attraction and repulsion. North and south poles of two magnets attract each other, while two north poles or two south poles repel each other. A magnet can exert force over a distance because the magnet is surrounded by a magnetic field. In the Figure 1.2, you can see the magnetic field surrounding a bar magnet. Tiny bits of iron, called iron filings, were placed under a sheet of glass. When the magnet was placed on the glass, it attracted the iron filings. The pattern of the iron filings shows the lines of force that make up the magnetic field of the magnet. The concentration of iron filings near the poles indicates that these areas exert the strongest force. You can also see how the magnetic field affects the compasses placed above the magnet. When two magnets are brought close together, their magnetic fields interact. You can see how they interact in the Figure 1.3. The lines of force of north and south poles attract each other whereas those of two north poles repel each other. | text | null |
L_0946 | mechanical advantage | T_4596 | How much a machine changes the input force is its mechanical advantage. Mechanical advantage is the ratio of the output force to the input force, so it can be represented by the equation: Actual Mechanical Advantage = Output force Input force Note that this equation represents the actual mechanical advantage of a machine. The actual mechanical advantage takes into account the amount of the input force that is used to overcome friction. The equation yields the factor by which the machine changes the input force when the machine is actually used in the real world. | text | null |
L_0946 | mechanical advantage | T_4597 | It can be difficult to measure the input and output forces needed to calculate the actual mechanical advantage of a machine. Generally, an unknown amount of the input force is used to overcome friction. Its usually easier to measure the input and output distances than the input and output forces. The distance measurements can then be used to calculate the ideal mechanical advantage. The ideal mechanical advantage represents the change in input force that would be achieved by the machine if there were no friction to overcome. The ideal mechanical advantage is always greater than the actual mechanical advantage because all machines have to overcome friction. Ideal mechanical advantage can be calculated with the equation: Ideal Mechanical Advantage = Input Distance Output Distance | text | null |
L_0946 | mechanical advantage | T_4598 | Look at the ramp in the Figure 1.1. A ramp is a type of simple machine called an inclined plane. It can be used to raise an object off the ground. The input distance is the length of the sloped surface of the ramp. This is the distance over which the input force is applied. The output distance is the height of the ramp, or the vertical distance the object is raised. For this ramp, the input distance is 6 m and the output distance is 2 meters. Therefore, the ideal mechanical advantage of this ramp is: Input distance Ideal Mechanical Advantage = Output distance = 62 m m =3 An ideal mechanical advantage of 3 means that the ramp ideally (in the absence of friction) multiplies the input force by a factor of 3. The trade-off is that the input force must be applied over a greater distance than the object is lifted. Q: Assume that another ramp has a sloping surface of 8 m and a vertical height of 4 m. What is the ideal mechanical advantage of this ramp? A: The ramp has an ideal mechanical advantage of: Ideal Mechanical Advantage = 84 m m =2 | text | null |
L_0946 | mechanical advantage | T_4599 | Many machinesincluding inclined planes such as rampsincrease the strength of the force put into the machine but decrease the distance over which the force is applied. Other machines increase the distance over which the force is applied but decrease the strength of the force. Still other machines change the direction of the force, with or without also increasing its strength or distance. Which way a machine works determines its mechanical advantage, as shown in the Table 1.1. Strength of Force increases decreases stays the same (changes direction only) Distance Over Force is Applied decreases increases stays the same which Mechanical Advantage Example >1 <1 =1 ramp hammer flagpole pulley | text | null |
L_0947 | mechanical wave | T_4600 | The waves in the picture above are examples of mechanical waves. A mechanical wave is a disturbance in matter that transfers energy through the matter. A mechanical wave starts when matter is disturbed. A source of energy is needed to disturb matter and start a mechanical wave. Q: Where does the energy come from in the water wave pictured above? A: The energy comes from the falling droplets of water, which have kinetic energy because of their motion. | text | null |
L_0947 | mechanical wave | T_4601 | The energy of a mechanical wave can travel only through matter. The matter through which the wave travels is called the medium (plural, media). The medium in the water wave pictured above is water, a liquid. But the medium of a mechanical wave can be any state of matter, even a solid. Q: How do the particles of the medium move when a wave passes through them? A: The particles of the medium just vibrate in place. As they vibrate, they pass the energy of the disturbance to the particles next to them, which pass the energy to the particles next to them, and so on. Particles of the medium dont actually travel along with the wave. Only the energy of the wave travels through the medium. | text | null |
L_0947 | mechanical wave | T_4602 | There are three types of mechanical waves: transverse, longitudinal, and surface waves. They differ in how particles of the medium move. You can see this in the Figure 1.1. In a transverse wave, particles of the medium vibrate up and down perpendicular to the direction of the wave. In a longitudinal wave, particles of the medium vibrate back and forth parallel to the direction of the wave. In a surface wave, particles of the medium vibrate both up and down and back and forth, so they end up moving in a circle. Q: How do you think surface waves are related to transverse and longitudinal waves? A: A surface wave is combination of a transverse wave and a longitudinal wave. | text | null |
L_0949 | mendeleevs periodic table | T_4606 | For many years, scientists looked for a good way to organize the elements. This became increasingly important as more and more elements were discovered. An ingenious method of organizing elements was developed in 1869 by a Russian scientist named Dmitri Mendeleev, who is pictured 1.1. Mendeleevs method of organizing elements was later revised, but it served as a basis for the method that is still used today. Mendeleev was a teacher as well as a chemist. He was writing a chemistry textbook and wanted to find a way to organize the 63 known elements so it would be easier for students to learn about them. He made a set of cards of the elements, similar to a deck of playing cards. On each card, he wrote the name of a different element, its atomic mass, and other known properties. Mendeleev arranged and rearranged the cards in many different ways, looking for a pattern. He finally found it when he placed the elements in order by increasing atomic mass. Q: What is atomic mass? Why might it be a good basis for organizing elements? A: Atomic mass is the mass of one atom of an element. It is about equal to the mass of the protons plus the neutrons in an atom. It is a good basis for organizing elements because each element has a unique number of protons and atomic mass is an indirect way of organizing elements by number of protons. | text | null |
L_0949 | mendeleevs periodic table | T_4607 | You can see how Mendeleev organized the elements in the Figure 1.2. From left to right across each row, elements are arranged by increasing atomic mass. Mendeleev discovered that if he placed eight elements in each row and then continued on to the next row, the columns of the table would contain elements with similar properties. He called the columns groups. They are sometimes called families, because elements within a group are similar but not identical to one another, like people in a family. Mendeleevs table of the elements is called a periodic table because of its repeating pattern. Anything that keeps repeating is referred to as periodic. Other examples of things that are periodic include the monthly phases of the moon and the daily cycle of night and day. The term period refers to the interval between repetitions. For example, the moons phases repeat every four weeks. In a periodic table of the elements, the periods are the rows of the table. In Mendeleevs table, each period contains eight elements, and then the pattern repeats in the next row. | text | null |
L_0949 | mendeleevs periodic table | T_4608 | Did you notice the blanks in Mendeleevs table? They are spaces that Mendeleev left blank for elements that had not yet been discovered when he created his table. He predicted that these missing elements would eventually be discovered. Based on their position in the table, he even predicted their properties. For example, he predicted a missing element in row 5 of group III. He also predicted that the missing element would have an atomic mass of 68 and be a relatively soft metal like other elements in this group. Scientists searched for the missing element, and they found it just a few years later. They named the new element gallium. Scientists searched for the other missing elements in Mendeleevs table and eventually found all of them. An important measure of a good model is its ability to make accurate predictions. This makes it a useful model. Clearly, Mendeleevs periodic table was a useful model. It helped scientists discover new elements and made sense of those that were already known. | text | null |
L_0950 | metallic bonding | T_4609 | Metallic bonds are forces of attraction between positive metal ions and the valence electrons that are constantly moving around them (see the Figure 1.1). The valence electrons include their own and those of other, nearby ions of the same metal. The valence electrons of metals move freely in this way because metals have relatively low electronegativity, or attraction to electrons. The positive metal ions form a lattice-like structure held together by all the metallic bonds. Click image to the left or use the URL below. URL: Q: Why do metallic bonds form only in elements that are metals? Why dont similar bonds form in elements that are nonmetals? A: Metal atoms readily give up valence electrons and become positive ions whenever they form bonds. When nonmetals bond together, the atoms share valence electrons and do not become ions. For example, when oxygen atoms bond together they form oxygen molecules in which two oxygen atoms share two pairs of valence electrons equally, so neither atom becomes charged. | text | null |
L_0950 | metallic bonding | T_4610 | The valence electrons surrounding metal ions are constantly moving. This makes metals good conductors of electricity. The lattice-like structure of metal ions is strong but quite flexible. This allows metals to bend without breaking. Metals are both ductile (can be shaped into wires) and malleable (can be shaped into thin sheets). Q: Look at the metalworker in the Figure 1.2. Hes hammering a piece of hot iron in order to shape it. Why doesnt the iron crack when he hits it? A: The iron ions can move within the sea of electrons around them. They can shift a little closer together or farther apart without breaking the metallic bonds between them. Therefore, the metal can bend rather than crack when the hammer hits it. | text | null |
L_0950 | metallic bonding | T_4610 | The valence electrons surrounding metal ions are constantly moving. This makes metals good conductors of electricity. The lattice-like structure of metal ions is strong but quite flexible. This allows metals to bend without breaking. Metals are both ductile (can be shaped into wires) and malleable (can be shaped into thin sheets). Q: Look at the metalworker in the Figure 1.2. Hes hammering a piece of hot iron in order to shape it. Why doesnt the iron crack when he hits it? A: The iron ions can move within the sea of electrons around them. They can shift a little closer together or farther apart without breaking the metallic bonds between them. Therefore, the metal can bend rather than crack when the hammer hits it. | text | null |
L_0951 | metalloids | T_4611 | Metalloids are the smallest class of elements. (The other two classes of elements are metals and nonmetals). There are just six metalloids. In addition to silicon, they include boron, germanium, arsenic, antimony, and tellurium. Metalloids fall between metals and nonmetals in the periodic table. They also fall between metals and nonmetals in terms of their properties. Q: How does the position of an element in the periodic table influence its properties? A: Elements are arranged in the periodic table by their atomic number, which is the number of protons in their atoms. Atoms are neutral in electric charge, so they always have the same number of electrons as protons. It is the number of electrons in the outer energy level of atoms that determines most of the properties of elements. | text | null |
L_0951 | metalloids | T_4612 | How metalloids behave in chemical interactions with other elements depends mainly on the number of electrons in the outer energy level of their atoms. Metalloids have from three to six electrons in their outer energy level. Boron, pictured in the Figure 1.1, is the only metalloid with just three electrons in its outer energy level. It tends to act like metals by giving up its electrons in chemical reactions. Metalloids with more than four electrons in their outer energy level (arsenic, antimony, and tellurium) tend to act like nonmetals by gaining electrons in chemical reactions. Those with exactly four electrons in their outer energy level (silicon and germanium) may act like either metals or nonmetals, depending on the other elements in the reaction. | text | null |
L_0951 | metalloids | T_4613 | Most metalloids have some physical properties of metals and some physical properties of nonmetals. For example, metals are good conductors of both heat and electricity, whereas nonmetals generally cannot conduct heat or electricity. And metalloids? They fall between metals and nonmetals in their ability to conduct heat, and if they can conduct electricity, they usually can do so only at higher temperatures. Metalloids that can conduct electricity at higher temperatures are called semiconductors. Silicon is an example of a semiconductor. It is used to make the tiny electric circuits in computer chips. You can see a sample of silicon and a silicon chip in the Figure 1.2. Metalloids tend to be shiny like metals but brittle like nonmetals. Because they are brittle, they may chip like glass or crumble to a powder if struck. Other physical properties of metalloids are more variable, including their boiling and melting points, although all metalloids exist as solids at room temperature. Click image to the left or use the URL below. URL: | text | null |
L_0952 | metals | T_4614 | Metals are elements that can conduct electricity. They are one of three classes of elements (the other two classes are nonmetals and metalloids). Metals are by far the largest of the three classes. In fact, most elements are metals. All of the elements on the left side and in the middle of the periodic table, except for hydrogen, are metals. There are several different types of metals, including alkali metals in group 1 of the periodic table, alkaline Earth metals in group 2, and transition metals in groups 3-12. The majority of metals are transition metals. | text | null |
L_0952 | metals | T_4615 | Elements in the same class share certain basic similarities. In addition to conducting electricity, many metals have several other shared properties, including those listed below. Metals have relatively high melting points. This explains why all metals except for mercury are solids at room temperature. Most metals are good conductors of heat. Thats why metals such as iron, copper, and aluminum are used for pots and pans. Metals are generally shiny. This is because they reflect much of the light that strikes them. The mercury pictured above is very shiny. The majority of metals are ductile. This means that they can be pulled into long, thin shapes, like the aluminum electric wires pictured in the Figure 1.1. Metals tend to be malleable. This means that they can be formed into thin sheets without breaking. An example is aluminum foil, also pictured in the Figure 1.1. Q: The defining characteristic of metals is their ability to conduct electricity. Why do you think metals have this property? A: The properties of metalsas well as of elements in the other classesdepend mainly on the number and arrangement of their electrons. | text | null |
L_0952 | metals | T_4616 | To understand why metals can conduct electricity, consider the metal lithium as an example. An atom of lithium is modeled below. Look at lithiums electrons. There are two electrons at the first energy level. This energy level can hold only two electrons, so it is full in lithium. The second energy level is another story. It can hold a maximum of eight electrons, but in lithium it has just one. A full outer energy level is the most stable arrangement of electrons. Lithium would need to gain seven electrons to fill its outer energy level and make it stable. Its far easier for lithium to give up its one electron in energy level 2, leaving it with a full outer energy level (now level 1). Electricity is a flow of electrons. Because lithium (like most other metals) easily gives up its extra electron, it is a good conductor of electricity. This tendency to give up electrons also explains other properties of metals such as lithium. | text | null |
L_0953 | microwaves | T_4617 | Electromagnetic waves carry energy through matter or space as vibrating electric and magnetic fields. Electromag- netic waves have a wide range of wavelengths and frequencies. The complete range is called the electromagnetic spectrum. The Figure 1.1 shows all the waves of the spectrum. The waves used in radar guns are microwaves. | text | null |
L_0953 | microwaves | T_4618 | Find the microwave in the Figure 1.1. A microwave is an electromagnetic wave with a relatively long wavelength and low frequency. Microwaves are often classified as radio waves, but they have higher frequencies than other radio waves. With higher frequencies, they also have more energy. Thats why microwaves are useful for heating food in microwave ovens. Microwaves have other important uses as well, including cell phone transmissions and radar. These uses are described below. Click image to the left or use the URL below. URL: | text | null |
L_0953 | microwaves | T_4619 | Cell phone signals are carried through the air as microwaves. You can see how this works in the Figure 1.2. A cell phone encodes the sounds of the callers voice in microwaves by changing the frequency of the waves. This is called frequency modulation. The encoded microwaves are then sent from the phone through the air to a cell tower. From the cell tower, the waves travel to a switching center. From there they go to another cell tower and from the tower to the receiver of the person being called. The receiver changes the encoded microwaves back to sounds. Q: Cell towers reach high above the ground. Why do you think such tall towers are used? A: Microwaves can be interrupted by buildings and other obstructions, so cell towers must be placed high above the ground to prevent the interruption of cell phone signals. | text | null |
L_0953 | microwaves | T_4620 | Radar stands for radio detection and ranging. In police radar, a radar gun sends out short bursts of microwaves. The microwaves reflect back from oncoming vehicles and are detected by a receiver in the radar gun. The frequency of the reflected waves is used to compute the speed of the vehicles. Radar is also used for tracking storms, detecting air traffic, and other purposes. Q: How are reflected microwaves used to determine the speed of oncoming cars (see Figure 1.3)? A: As the car approaches the radar gun, the reflected microwaves get bunched up in front of the car. Therefore, the waves the receiver detects have a higher frequency than they would if they were being reflected from a stationary object. The faster the car is moving, the greater the increase in the frequency of the waves. This is an example of the Doppler effect, which can also occur with sound waves. | text | null |
L_0954 | mirrors | T_4621 | A mirror is typically made of glass with a shiny metal backing that reflects all the light that strikes it. When a mirror reflects light, it forms an image. An image is a copy of an object that is formed by reflection or refraction. Mirrors may have flat or curved surfaces. The shape of a mirrors surface determines the type of image it forms. For example, some mirrors form real images, and other mirrors form virtual images. Whats the difference between real and virtual images? A real image forms in front of a mirror where reflected light rays actually meet. It is a true image that could be projected on a screen. A virtual image appears to be on the other side of the mirror. Of course, reflected rays dont actually go through the mirror to the other side, so a virtual image doesnt really exist. It just appears to exist to the human brain. Q: Look back at the image of the girl pointing at her image in the mirror. Which type of image is it, real or virtual? A: The image of the girl is a virtual image. It appears to be on the other side of the mirror from the girl. | text | null |
L_0954 | mirrors | T_4622 | The mirror in the opening photo is a plane mirror. This is the most common type of mirror. It has a flat reflective surface and forms only virtual images. The image formed by a plane mirror is also right-side up and life sized. But something is different about the image compared with the real object in front of the mirror. Left and right are reversed. Look at the girl brushing her teeth in the Figure 1.1. She is using her left hand to brush her teeth, but her image (on the left) appears to be brushing her teeth with the right hand. All plane mirrors reverse left and right in this way. The term mirror image refers to how left and right are reversed in an image compared with the object. | text | null |
L_0954 | mirrors | T_4623 | Some mirrors have a curved rather than flat surface. Curved mirrors can be concave or convex. A concave mirror is shaped like the inside of a bowl. This type of mirror forms either real or virtual images, depending on where the object is placed relative to the focal point. The focal point is the point in front of the mirror where the reflected rays meet. You can see how concave mirrors form images in the Figure 1.2. Concave mirrors are used behind car headlights. They focus the light and make it brighter. Concave mirrors are also used in some telescopes. | text | null |
L_0954 | mirrors | T_4624 | The other type of curved mirror, a convex mirror, is shaped like the outside of a bowl. Because of its shape, it can gather and reflect light from a wide area. As you can see in the Figure 1.3, a convex mirror forms only virtual images that are right-side up and smaller than the actual object. Q: Convex mirrors are used as side mirrors on cars. You can see one in the Figure 1.4. Why is a convex mirror good for this purpose? A: Because it gathers light over a wide area, a convex mirror gives the driver a wider view of the area around the vehicle than a plane mirror would. | text | null |
L_0954 | mirrors | T_4624 | The other type of curved mirror, a convex mirror, is shaped like the outside of a bowl. Because of its shape, it can gather and reflect light from a wide area. As you can see in the Figure 1.3, a convex mirror forms only virtual images that are right-side up and smaller than the actual object. Q: Convex mirrors are used as side mirrors on cars. You can see one in the Figure 1.4. Why is a convex mirror good for this purpose? A: Because it gathers light over a wide area, a convex mirror gives the driver a wider view of the area around the vehicle than a plane mirror would. | text | null |
L_0956 | modern periodic table | T_4629 | In the 1860s, a scientist named Dmitri Mendeleev also saw the need to organize the elements. He created a table in which he arranged all of the elements by increasing atomic mass from left to right across each row. When he placed eight elements in each row and then started again in the next row, each column of the table contained elements with similar properties. He called the columns of elements groups. Mendeleevs table is called a periodic table and the rows are called periods. Thats because the table keeps repeating from row to row, and periodic means repeating. | text | null |
L_0956 | modern periodic table | T_4630 | A periodic table is still used today to organize the elements. You can see a simple version of the modern periodic table in the Figure 1.1. The modern table is based on Mendeleevs table, except the modern table arranges the elements by increasing atomic number instead of atomic mass. Atomic number is the number of protons in an atom, and this number is unique for each element. The modern table has more elements than Mendeleevs table because many elements have been discovered since Mendeleevs time. | text | null |
L_0956 | modern periodic table | T_4631 | In the Figure 1.1, each element is represented by its chemical symbol, which consists of one or two letters. The first letter of the symbol is always written in upper case, and the second letterif there is oneis always written in lower case. For example, the symbol for copper is Cu. It stands for cuprum, which is the Latin word for copper. The number above each symbol in the table is its unique atomic number. Notice how the atomic numbers increase from left to right and from top to bottom in the table. Q: Find the symbol for copper in the Figure 1.1. What is its atomic number? What does this number represent? A: The atomic number of copper is 29. This number represents the number of protons in each atom of copper. (Copper is the element that makes up the coil of wire in photo A of the opening sequence of photos.) | text | null |
L_0956 | modern periodic table | T_4632 | Rows of the modern periodic table are called periods, as they are in Mendeleevs table. From left to right across a period, each element has one more proton than the element before it. Some periods in the modern periodic table are longer than others. For example, period 1 contains only two elements: hydrogen (H) and helium (He). In contrast, periods 6 and 7 are so long that many of their elements are placed below the main part of the table. They are the elements starting with lanthanum (La) in period 6 and actinium (Ac) in period 7. Some elements in period 7 have not yet been named. They are represented by temporary three-letter symbols, such as Uub. The number of each period represents the number of energy levels that have electrons in them for atoms of each element in that period. Q: Find calcium (Ca) in the Figure 1.1. How many energy levels have electrons in them for atoms of calcium? A: Calcium is in period 4, so its atoms have electrons in them for the first four energy levels. | text | null |
L_0956 | modern periodic table | T_4633 | Columns of the modern table are called groups, as they are in Mendeleevs table. However, the modern table has many more groups18 compared with just 8 in Mendeleevs table. Elements in the same group have similar properties. For example, all elements in group 18 are colorless, odorless gases, such as neon (Ne). (Neon is the element inside the light in opening photo C.) In contrast, all elements in group 1 are very reactive solids. They react explosively with water, as you can see in the video and Figure 1.2. Click image to the left or use the URL below. URL: The alkali metal sodium (Na) reacting with water. | text | null |
L_0956 | modern periodic table | T_4634 | All elements can be classified in one of three classes: metals, metalloids, or nonmetals. Elements in each class share certain basic properties. For example, elements in the metals class can conduct electricity, whereas elements in the nonmetals class generally cannot. Elements in the metalloids class fall in between the metals and nonmetals in their properties. An example of a metalloid is arsenic (As). (Arsenic is the element in opening photo B.) In the periodic table above, elements are color coded to show their class. As you move from left to right across each period of the table, the elements change from metals to metalloids to nonmetals. Q: To which class of elements does copper (Cu) belong: metal, metalloid, or nonmetal? Identify three other elements in this class. A: In the Figure 1.1, the cell for copper is colored blue. This means that copper belongs to the metals class. Other elements in the metals class include iron (Fe), sodium (Na), and gold (Au). It is apparent from the table that the majority of elements are metals. | text | null |
L_0957 | molecular compounds | T_4635 | Compounds that form from two or more nonmetallic elements, such as carbon and hydrogen, are called covalent compounds. In a covalent compound, atoms of the different elements are held together in molecules by covalent bonds. These are chemical bonds in which atoms share valence electrons. The force of attraction between the shared electrons and the positive nuclei of both atoms holds the atoms together in the molecule. A molecule is the smallest particle of a covalent compound that still has the properties of the compound. The largest, most complex covalent molecules have thousands of atoms. Examples include proteins and carbohy- drates, which are compounds in living things. The smallest, simplest covalent compounds have molecules with just two atoms. An example is hydrogen chloride (HCl). It consists of one hydrogen atom and one chlorine atom, as you can see in the Figure 1.1. | text | null |
L_0957 | molecular compounds | T_4636 | To name simple covalent compounds, follow these rules: Start with the name of the element closer to the left side of the periodic table. Follow this with the name of element closer to the right of the periodic table. Give this second name the suffix -ide. Use prefixes to represent the numbers of the different atoms in each molecule of the compound. The most commonly used prefixes are shown in the Table 1.1. Number 1 2 3 4 5 6 Prefix mono- (or none) di- tri- tetra- penta- hexa- Q: What is the name of the compound that contains three oxygen atoms and two nitrogen atoms? A: The compound is named dinitrogen trioxide. Nitrogen is named first because it is farther to the left in the periodic table than oxygen. Oxygen is given the -ide suffix because it is the second element named in the compound. The prefix di- is added to nitrogen to show that there are two atoms of nitrogen in each molecule of the compound. The prefix tri- is added to oxygen to show that there are three atoms of oxygen in each molecule. In the chemical formula for a covalent compound, the numbers of the different atoms in a molecule are represented by subscripts. For example, the formula for the compound named carbon dioxide is CO2 . Q: What is the chemical formula for dinitrogen trioxide? A: The chemical formula is N2 O3 . | text | null |
L_0957 | molecular compounds | T_4637 | The covalent bonds of covalent compounds are responsible for many of the properties of the compounds. Because valence electrons are shared in covalent compounds, rather than transferred between atoms as they are in ionic compounds, covalent compounds have very different properties than ionic compounds. Many covalent compounds, especially those containing carbon and hydrogen, burn easily. In contrast, many ionic compounds do not burn. Many covalent compounds do not dissolve in water, whereas most ionic compounds dissolve well in water. Unlike ionic compounds, covalent compounds do not have freely moving electrons, so they cannot conduct Name of Compound(Chemical For- mula) Sodium chloride (NaCl) Lithium fluoride (LiF) Type of Compound Boiling Point ( C) ionic ionic 1413 1676 Q: The two covalent compounds in the table are gases at room temperature, which is 20 C. For a compound to be a liquid at room temperature, what does its boiling point have to be? A: To be a liquid at room temperature, a covalent compound has to have a boiling point higher than 20 C. Water is an example of a covalent compound that is a liquid at room temperature. The boiling point of water is 100 C. | text | null |
L_0958 | momentum | T_4638 | Momentum is a property of a moving object that makes it hard to stop. The more mass it has or the faster its moving, the greater its momentum. Momentum equals mass times velocity and is represented by the equation: Momentum = Mass Velocity Q: What is Codys momentum as he stands at the top of the ramp? A: Cody has no momentum as he stands there because he isnt moving. In other words, his velocity is zero. However, Cody will gain momentum as he starts moving down the ramp and picks up speed. Q: Codys older brother Jerod is pictured in the Figure 1.1. If Jerod were to travel down the ramp at the same velocity as Cody, who would have greater momentum? Who would be harder to stop? A: Jerod obviously has greater mass than Cody, so he would have greater momentum. He would also be harder to stop. | text | null |
L_0958 | momentum | T_4639 | To calculate momentum with the equation above, mass is measured in (kg), and velocity is measured in meters per second (m/s). For example, Cody and his skateboard have a combined mass of 40 kg. If Cody is traveling at a velocity of 1.1 m/s by the time he reaches the bottom of the ramp, then his momentum is: Momentum = 40 kg 1.1 m/s = 44 kg m/s Note that the SI unit for momentum is kg m/s. Q: The combined mass of Jerod and his skateboard is 68 kg. If Jerod goes down the ramp at the same velocity as Cody, what is his momentum at the bottom of the ramp? A: His momentum is: Momentum = 68 kg 1.1 m/s = 75 kg m/s | text | null |
L_0959 | motion | T_4640 | In science, motion is defined as a change in position. An objects position is its location. Besides the wings of the hummingbird in the opening image, you can see other examples of motion in the Figure 1.1. In each case, the position of something is changing. Q: In each picture in the Figure 1.1, what is moving and how is its position changing? A: The train and all its passengers are speeding straight down a track to the next station. The man and his bike are racing along a curving highway. The geese are flying over their wetland environment. The meteor is shooting through the atmosphere toward Earth, burning up as it goes. | text | null |
L_0959 | motion | T_4641 | Theres more to motion than objects simply changing position. Youll see why when you consider the following example. Assume that the school bus pictured in the Figure 1.2 passes by you as you stand on the sidewalk. Its obvious to you that the bus is moving, but what about to the children inside the bus? The bus isnt moving relative to them, and if they look at the other children sitting on the bus, they wont appear to be moving either. If the ride is really smooth, the children may only be able to tell that the bus is moving by looking out the window and seeing you and the trees whizzing by. This example shows that how we perceive motion depends on our frame of reference. Frame of reference refers to something that is not moving with respect to an observer that can be used to detect motion. For the children on the bus, if they use other children riding the bus as their frame of reference, they do not appear to be moving. But if they use objects outside the bus as their frame of reference, they can tell they are moving. Q: What is your frame of reference if you are standing on the sidewalk and see the bus go by? How can you tell that the bus is moving? A: Your frame of reference might be the trees and other stationary objects across the street. As the bus goes by, it momentarily blocks your view of these objects, and this helps you detect the bus motion. | text | null |
L_0959 | motion | T_4641 | Theres more to motion than objects simply changing position. Youll see why when you consider the following example. Assume that the school bus pictured in the Figure 1.2 passes by you as you stand on the sidewalk. Its obvious to you that the bus is moving, but what about to the children inside the bus? The bus isnt moving relative to them, and if they look at the other children sitting on the bus, they wont appear to be moving either. If the ride is really smooth, the children may only be able to tell that the bus is moving by looking out the window and seeing you and the trees whizzing by. This example shows that how we perceive motion depends on our frame of reference. Frame of reference refers to something that is not moving with respect to an observer that can be used to detect motion. For the children on the bus, if they use other children riding the bus as their frame of reference, they do not appear to be moving. But if they use objects outside the bus as their frame of reference, they can tell they are moving. Q: What is your frame of reference if you are standing on the sidewalk and see the bus go by? How can you tell that the bus is moving? A: Your frame of reference might be the trees and other stationary objects across the street. As the bus goes by, it momentarily blocks your view of these objects, and this helps you detect the bus motion. | text | null |
L_0960 | musical instruments | T_4642 | People have been using sound to make music for thousands of years. They have invented many different kinds of musical instruments. Despite their diversity, however, musical instruments share certain similarities. All musical instruments create sound by causing matter to vibrate. The vibrations start sound waves moving through the air. Most musical instruments use resonance to amplify the sound waves and make the sounds louder. Resonance occurs when an object vibrates in response to sound waves of a certain frequency. In a musical instrument such as a drum, the whole instrument and the air inside it may vibrate when the head of the drum is struck. Most musical instruments have a way of changing the frequency of the sound waves they produce. This changes the pitch of the sounds, or how high or low the sounds seem to a listener. | text | null |
L_0960 | musical instruments | T_4643 | There are three basic categories of musical instruments: percussion, wind, and stringed instruments. You can read in the Figure 1.1 how instruments in each category make sound and change pitch. Q: Can you name other instruments in each of the three categories of musical instruments? A: Other percussion instruments include drums and cymbals. Other wind instruments include trumpets and flutes. Other stringed instruments include guitars and harps. | text | null |
L_0962 | nature of technology | T_4647 | Printers like the one that made the plastic bicycle are a new type of technology. Technology is the application of science to solve problems. Because technology finds solutions to practical problems, new technologies may have major impacts on society, science, and industry. For example, some people predict that 3-D printing will revolutionize manufacturing. Q: Making products with 3-D printers has several advantages over making them with machines in factories. What do you think some of the advantages might be? A: Making products with 3-D printers would allow anyone anywhere to make just about anything, provided they have the printer, powder, and computer program. Suppose, for example, that you live in a remote location and need a new part for your car. The solution? Just download the design on your computer and print the part on your 3-D printer. Manufacturing would no longer require specially designed machines in factories that produce pollution. Another advantage of using 3-D printers to make products is that no materials are wasted. This would lower manufacturing costs as well as save natural resources. | text | null |
L_0962 | nature of technology | T_4648 | New technologies such as 3-D printers often evolve slowly as new materials, designs, or processes are invented. Solar-powered cars are a good example. For several decades, researchers have been working on developing practical solar-powered cars. Why? Cars powered by sunlight have at least two important advantages over gas-powered cars. The energy they use is free and available almost everywhere, and they produce no pollution. The timeline in Table Milestone 1954: First modern solar cell 1955: First solar car 1983: First practical solar car 1987: First World Solar Challenge 2008: First Commercial solar car The first modern solar cell was invented in 1954 by a team of researchers at Bell Labs in the U.S. It could convert light energy to enough electricity to power devices. In 1955, William G. Cobb of General Motors demon- strated his 15-inch-long Sunmobile, the worlds first solar-powered automobile. Its tiny electric motor was powered by 12 solar cells on top of the car. In 1983, the first drivable solar car was created by Hans Tholstrup, a Danish inventor who was influenced by the earlier Sunmobile. Called the Quiet Achiever, Tholstrups car was driven 4000 km across Australia. However, its average speed was only 23 km/h, despite having more than 700 solar cells on its top panel. Inspired by his success with the Quiet Achiever, in 1987 Tholstrup launched the first World Solar Chal- lenge. This was the worlds first solar car race. The race is now held every other year. In that first race, the winner was General Motors Sunraycer, shown here. It had an average speed of 67 km/h. Its aerodynamic shape helped it achieve that speed. In 2008, the first commercial solar car was introduced. Called the Venturi Astrolab, it has a top speed of 120 km/h. To go this fast while using very little energy, it is built of ultra-light materials. Its oversized body protects the driver in case of collision and provides a lot of surface area for solar cells. Q: Why was the invention of the solar cell important to the evolution of solar car technology? A: The solar car could not exist without the solar cell. This invention provided a way to convert light energy to electricity that could be used to run a device such as a car. Q: The 1955 Sunmobile was just a model car. It was too small for people to drive. Why was it an important achievement in the evolution of solar car technology? A: The car wasnt practical, but it was a working solar car. It showed people that solar car technology is possible. It spurred others, including Hans Tholstrup, to work on solar cars that people could actually drive. Q: How have the World Solar Challenge races influenced the development of solar cars? A: The races have drawn a lot of attention to solar car development. The challenge of winning a race has also stimulated developers to keep improving the performance of solar cars so they can go faster and farther on solar power alone. | text | null |
L_0963 | neutrons | T_4649 | A neutron is one of three main particles that make up the atom. The other two particles are the proton and electron. Atoms of all elementsexcept for most atoms of hydrogenhave neutrons in their nucleus. The nucleus is the small, dense region at the center of an atom where protons are also found. Atoms generally have about the same number of neutrons as protons. For example, all carbon atoms have six protons and most also have six neutrons. A model of a carbon atom is shown in the Figure 1.1. Click image to the left or use the URL below. URL: | text | null |
L_0963 | neutrons | T_4650 | Unlike protons and electrons, which are electrically charged, neutrons have no charge. In other words, they are electrically neutral. Thats why the neutrons in the diagram above are labeled n0 . The zero stands for zero charge. The mass of a neutron is slightly greater than the mass of a proton, which is 1 atomic mass unit (amu). (An atomic mass unit equals about 1.67 1027 kilograms.) A neutron also has about the same diameter as a proton, or 1.7 1017 meters. | text | null |
L_0963 | neutrons | T_4651 | All the atoms of a given element have the same number of protons and electrons. The number of neutrons, however, may vary for atoms of the same element. For example, almost 99 percent of carbon atoms have six neutrons, but the rest have either seven or eight neutrons. Atoms of an element that differ in their numbers of neutrons are called isotopes. The nuclei of these isotopes of carbon are shown in the Figure 1.2. The isotope called carbon-14 is used to find the ages of fossils. Q: Notice the names of the carbon isotopes in the diagram. Based on this example, infer how isotopes of an element are named. A: Isotopes of an element are named for their total number of protons and neutrons. Q: The element oxygen has 8 protons. How many protons and neutrons are there in oxygen-17? A: Oxygen-17like all atoms of oxygenhas 8 protons. Its name provides the clue that it has a total of 17 protons and neutrons. Therefore, it must have 9 neutrons (8 + 9 = 17). | text | null |
L_0963 | neutrons | T_4652 | Neutrons consist of fundamental particles known as quarks and gluons. Each neutron contains three quarks, as shown in the diagram below. Two of the quarks are called down quarks (d) and the third quark is called an up quark (u). Gluons (represented by wavy black lines in the diagram) are fundamental particles that are given off or absorbed by quarks. They carry the strong nuclear force that holds together quarks in a neutron. | text | null |
L_0964 | newtons first law | T_4653 | Did you ever ride a skateboard? Even if you didnt, you probably know that to start a skateboard rolling over a level surface, you need to push off with one foot against the ground. Thats what Coreys friend Nina is doing in this picture 1.1. Do you know how to stop a skateboard once it starts rolling? Look how Ninas friend Laura does it in the Figure the skateboard. Even if Laura didnt try to stop the skateboard, it would stop sooner or later. Thats because theres also friction between the wheels and the pavement. Friction is a force that counters all kinds of motion. It occurs whenever two surfaces come into contact. | text | null |
L_0964 | newtons first law | T_4653 | Did you ever ride a skateboard? Even if you didnt, you probably know that to start a skateboard rolling over a level surface, you need to push off with one foot against the ground. Thats what Coreys friend Nina is doing in this picture 1.1. Do you know how to stop a skateboard once it starts rolling? Look how Ninas friend Laura does it in the Figure the skateboard. Even if Laura didnt try to stop the skateboard, it would stop sooner or later. Thats because theres also friction between the wheels and the pavement. Friction is a force that counters all kinds of motion. It occurs whenever two surfaces come into contact. | text | null |
L_0964 | newtons first law | T_4654 | If you understand how a skateboard starts and stops, then you already know something about Newtons first law of motion. This law was developed by English scientist Isaac Newton around 1700. Newton was one of the greatest scientists of all time. He developed three laws of motion and the law of gravity, among many other contributions. Newtons first law of motion states that an object at rest will remain at rest and an object in motion will stay in motion unless it is acted on by an unbalanced force. Without an unbalanced force, a moving object will not only keep moving, but its speed and direction will also remain the same. Newtons first law of motion is often called the law of inertia because inertia is the tendency of an object to resist a change in its motion. If an object is already at rest, inertia will keep it at rest. If an object is already in motion, inertia will keep it moving. | text | null |
L_0964 | newtons first law | T_4655 | Coreys friend Jerod likes to skate on the flat banks at Newtons Skate Park. Thats Jerod in the Figure 1.3. As he reaches the top of a bank, he turns his skateboard to go back down. To change direction, he presses down with his heels on one edge of the skateboard. This causes the skateboard to turn in the opposite direction. | text | null |
L_0964 | newtons first law | T_4656 | Q: How does Nina use Newtons first law to start her skateboard rolling? A: The skateboard wont move unless Nina pushes off from the pavement with one foot. The force she applies when she pushes off is stronger than the force of friction that opposes the skateboards motion. As a result, the force on the skateboard is unbalanced, and the skateboard moves forward. Q: How does Nina use Newtons first law to stop her skateboard? A: Once the skateboard starts moving, it would keep moving at the same speed and in the same direction if not for another unbalanced force. That force is friction between the skateboard and the pavement. The force of friction is unbalanced because Nina is no longer pushing with her foot to keep the skateboard moving. Thats why the skateboard stops. Q: How does Jerod use Newtons first law of motion to change the direction of his skateboard? A: Pressing down on just one side of a skateboard creates an unbalanced force. The unbalanced force causes the skateboard to turn toward the other side. In the picture, Jerod is pressing down with his heels, so the skateboard turns toward his toes. | text | null |
L_0965 | newtons law of gravity | T_4657 | Newton was the first one to suggest that gravity is universal and affects all objects in the universe. Thats why Newtons law of gravity is called the law of universal gravitation. Universal gravitation means that the force that causes an apple to fall from a tree to the ground is the same force that causes the moon to keep moving around Earth. Universal gravitation also means that while Earth exerts a pull on you, you exert a pull on Earth. In fact, there is gravity between you and every mass around youyour desk, your book, your pen. Even tiny molecules of gas are attracted to one another by the force of gravity. Q: Newtons law of universal gravitation had a huge impact on how people thought about the universe. Why do you think it was so important? A: Newtons law was the first scientific law that applied to the entire universe. It explains the motion of objects not only on Earth but in outer space as well. | text | null |
L_0965 | newtons law of gravity | T_4658 | Newtons law also states that the strength of gravity between any two objects depends on two factors: the masses of the objects and the distance between them. Objects with greater mass have a stronger force of gravity between them. For example, because Earth is so massive, it attracts you and your desk more strongly that you and your desk attract each other. Thats why you and the desk remain in place on the floor rather than moving toward one another. Objects that are closer together have a stronger force of gravity between them. For example, the moon is closer to Earth than it is to the more massive sun, so the force of gravity is greater between the moon and Earth than between the moon and the sun. Thats why the moon circles around Earth rather than the sun. You can see this in the Figure 1.1. | text | null |
L_0966 | newtons second law | T_4659 | Whenever an object speeds up, slows down, or changes direction, it accelerates. Acceleration occurs whenever an unbalanced force acts on an object. Two factors affect the acceleration of an object: the net force acting on the object and the objects mass. Newtons second law of motion describes how force and mass affect acceleration. The law states that the acceleration of an object equals the net force acting on the object divided by the objects mass. This can be represented by the equation: Acceleration = or a = Net force Mass F m Q: While Tony races along on his rollerblades, what net force is acting on the skates? A: Tony exerts a backward force against the ground, as you can see in the Figure 1.1, first with one skate and then with the other. This force pushes him forward. Although friction partly counters the forward motion of the skates, it is weaker than the force Tony exerts. Therefore, there is a net forward force on the skates. | text | null |
L_0966 | newtons second law | T_4660 | Newtons second law shows that there is a direct relationship between force and acceleration. The greater the force that is applied to an object of a given mass, the more the object will accelerate. For example, doubling the force on the object doubles its acceleration. The relationship between mass and acceleration is different. It is an inverse relationship. In an inverse relationship, when one variable increases, the other variable decreases. The greater the mass of an object, the less it will accelerate when a given force is applied. For example, doubling the mass of an object results in only half as much acceleration for the same amount of force. Q: Tony has greater mass than the other two boys he is racing (pictured in the opening image). How will this affect his acceleration around the track? A: Tonys greater mass will result in less acceleration for the same amount of force. | text | null |
L_0967 | newtons third law | T_4661 | Newtons third law of motion explains how Jerod starts his skateboard moving. This law states that every action has an equal and opposite reaction. This means that forces always act in pairs. First an action occursJerod pushes against the ground with his foot. Then a reaction occursJerod moves forward on his skateboard. The reaction is always equal in strength to the action but in the opposite direction. Q: If Jerod pushes against the ground with greater force, how will this affect his forward motion? A: His action force will be greater, so the reaction force will be greater as well. Jerod will be pushed forward with more force, and this will make him go faster and farther. | text | null |
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