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L_0850 | crystalline carbon | T_4290 | A fullerene (also called a Bucky ball) is a form of carbon in which carbon atoms are arranged in a hollow sphere resembling a soccer ball (see Figure 1.4). Each sphere contains 60 carbon atoms, and each carbon atom is bonded to three others by single covalent bonds. The bonds are relatively weak, so fullerenes can dissolve and form solutions. Fullerenes were first discovered in 1985 and have been found in soot and meteorites. Possible commercial uses of fullerenes are under investigation. Fullerene Crystal | text | null |
L_0851 | daltons atomic theory | T_4291 | Around 1800, the English chemist John Dalton brought back Democritus ancient idea of the atom. You can see a picture of Dalton 1.1. Dalton grew up in a working-class family. As an adult, he made a living by teaching and just did research in his spare time. Nonetheless, from his research he developed one of the most important theories in all of science. Based on his research results, he was able to demonstrate that atoms actually do exist, something that Democritus had only guessed. | text | null |
L_0851 | daltons atomic theory | T_4292 | Dalton did many experiments that provided evidence for the existence of atoms. For example: He investigated pressure and other properties of gases, from which he inferred that gases must consist of tiny, individual particles that are in constant, random motion. He researched the properties of compounds, which are substances that consist of more than one element. He showed that a given compound is always comprised of the same elements in the same whole-number ratio and that different compounds consist of different elements or ratios. This can happen, Dalton reasoned, only if elements are made of separate, discrete particles that cannot be subdivided. | text | null |
L_0851 | daltons atomic theory | T_4293 | From his research, Dalton developed a theory about atoms. Daltons atomic theory consists of three basic ideas: All substances are made of atoms. Atoms are the smallest particles of matter. They cannot be divided into smaller particles, created, or destroyed. All atoms of the same element are alike and have the same mass. Atoms of different elements are different and have different masses. Atoms join together to form compounds, and a given compound always consists of the same kinds of atoms in the same proportions. Daltons atomic theory was accepted by many scientists almost immediately. Most of it is still accepted today. However, scientists now know that atoms are not the smallest particles of matter. Atoms consist of several types of smaller particles, including protons, neutrons, and electrons. | text | null |
L_0851 | daltons atomic theory | T_4294 | Because Dalton thought atoms were the smallest particles of matter, he envisioned them as solid, hard spheres, like billiard (pool) balls, so he used wooden balls to model them. Three of his model atoms are pictured in the Figure and used to model compounds. Q: When scientists discovered smaller particles inside the atom, they realized that Daltons atomic models were too simple. How do modern atomic models differ from Daltons models? A: Modern atomic models, like the one pictured at the top of this article, usually represent subatomic particles, including electrons, protons, and neutrons. | text | null |
L_0852 | dangers and uses of radiation | T_4295 | A low level of radiation occurs naturally in the environment. This is called background radiation. One source of background radiation is rocks, which may contain small amounts of radioactive elements such as uranium. Another source is cosmic rays. These are charged particles that arrive on Earth from outer space. Background radiation is generally considered to be safe for living things. | text | null |
L_0852 | dangers and uses of radiation | T_4296 | Long-term or high-dose exposure to radiation can harm both living and nonliving things. Radiation knocks electrons out of atoms and changes them to ions. It also breaks bonds in DNA and other compounds in living things. One source of radiation that is especially dangerous to people is radon. Radon is a radioactive gas that forms in rocks underground. It can seep into basements and get trapped inside buildings. Then it may build up and become harmful to people who breathe it. Long-term exposure to radon can cause lung cancer. Exposure to higher levels of radiation can be very dangerous, even if the exposure is short-term. A single large dose of radiation can burn the skin and cause radiation sickness. Symptoms of this illness include extreme fatigue, destruction of blood cells, and loss of hair. Nonliving things can also be damaged by radiation. For example, high levels of radiation can weaken metals by removing electrons. This is a problem in nuclear power plants and space vehicles because they are exposed to very high levels of radiation. Q: Can you tell when you are being exposed to radiation? For example, can you sense radon in the air? A: Radiation cant be detected with the senses. This adds to its danger. However, there are other ways to detect it. | text | null |
L_0852 | dangers and uses of radiation | T_4297 | You generally cant see, smell, taste, hear, or feel radiation. Fortunately, there are devices such as Geiger counters that can detect radiation. A Geiger counter, like the one pictured in the Figure 1.1, contains atoms of a gas that is ionized if it encounters radiation. When this happens, the gas atoms change to ions that can carry an electric current. The current causes the Geiger counter to click. The faster the clicks occur, the higher the level of radiation. | text | null |
L_0852 | dangers and uses of radiation | T_4298 | Despite its dangers, radioactivity has several uses. For example, it can be used to determine the ages of ancient rocks and fossils. It can also be used as a source of power to generate electricity. Radioactivity can even be used to diagnose and treat diseases, including cancer. Cancer cells grow rapidly and take up a lot of glucose for energy. Glucose containing radioactive elements can be given to patients. Cancer cells take up more of the glucose than normal cells do and give off radiation. The radiation can be detected with special machines like the one in the Figure 1.2. The radiation may also kill cancer cells. | text | null |
L_0853 | decomposition reactions | T_4299 | A decomposition reaction occurs when one reactant breaks down into two or more products. It can be represented by the general equation: AB A + B In this equation, AB represents the reactant that begins the reaction, and A and B represent the products of the reaction. The arrow shows the direction in which the reaction occurs. Q: What is the chemical equation for the decomposition of hydrogen peroxide (H2 O2 ) to water (H2 O) and oxygen (O2 )? A: The equation for this decomposition reaction is: 2 H2 O2 2 H2 O + O2 | text | null |
L_0853 | decomposition reactions | T_4300 | Two more examples of decomposition reactions are described below. Carbonic acid (H2 CO3 ) is an ingredient in soft drinks. A decomposition reaction takes place when carbonic acid breaks down to produce water (H2 O) and carbon dioxide (CO2 ). This occurs when you open a can of soft drink and some of the carbon dioxide fizzes out. The equation for this reaction is: H2 CO3 H2 O + CO2 Another decomposition reaction occurs when water (H2 O) breaks down to produce hydrogen (H2 ) and oxygen (O2 ) gases (see Figure 1.1). This happens when an electric current passes through the water, as illustrated below. The equation for this reaction is: 2 H2 O 2 H2 + O2 Decomposition of water. Q: What ratio of hydrogen molecules (H2 ) to oxygen molecules (O2 ) is produced in the decomposition of water? A: Two hydrogen molecules per oxygen molecule are produced because water (H2 O) has a ratio of two hydrogen atoms to one oxygen atom. | text | null |
L_0854 | democrituss idea of the atom | T_4301 | Democritus lived in Greece from about 460 to 370 B.C.E. Like many other ancient Greek philosophers, he spent a lot of time wondering about the natural world. Democritus wondered, for example, what would happen if you cut a chunk of mattersuch as a piece of cheese into smaller and smaller pieces. He thought that a point would be reached at which the cheese could not be cut into still smaller pieces. He called these pieces atomos, which means uncuttable in Greek. This is where the modern term atom comes from. | text | null |
L_0854 | democrituss idea of the atom | T_4302 | Democritus idea of the atom has been called the best guess in antiquity. Thats because it was correct in many ways, yet it was based on pure speculation. It really was just a guess. Heres what Democritus thought about the atom: How many times could you cut this piece of cheese in half? How small would the smallest pieces be? All matter consists of atoms, which cannot be further subdivided into smaller particles. Atoms are extremely smalltoo small to see. Atoms are solid particles that are indestructible. Atoms are separated from one another by emptiness, or void. Q: How are Democrituss ideas about atoms similar to modern ideas about atoms? A: Modern ideas agree that all matter is made up of extremely small building blocks called atoms. Q: How are Democrituss ideas different from modern ideas? A: Although atoms are extremely small, it is now possible to see them with very powerful microscopes. Atoms also arent the solid, uncuttable particles Democritus thought. Instead, they consist of several kinds of smaller, simpler particles as well as a lot of empty space. In addition, atoms arent really indestructible because they can be changed to other forms of matter or energy. | text | null |
L_0854 | democrituss idea of the atom | T_4303 | Did you ever notice dust motes moving in still air where a beam of sunlight passes through it? You can see an example in the forest scene in the Figure 1.2. This sort of observation gave Democritus the idea that atoms are in constant, random motion. If this were true, Democritus thought, then atoms must always be bumping into each other. When they do, he surmised, they either bounce apart or stick together to form clumps of atoms. Eventually, the clumps could grow big enough to be visible matter. Q: Which modern theory of matter is similar to Democritus ideas about the motion of atoms? A: The modern kinetic theory of matter is remarkably similar to Democritus ideas about the motion of atoms. According to this theory, atoms of matter are in constant random motion. This motion is greater in gases than in liquids, and it is greater in liquids than in solids. But even in solids, atoms are constantly vibrating in place. | text | null |
L_0854 | democrituss idea of the atom | T_4304 | Democritus thought that different kinds of matter vary because of the size, shape, and arrangement of their atoms. For example, he suggested that sweet substances are made of smooth atoms and bitter substances are made of sharp atoms. He speculated that atoms of liquids are slippery, which allows them to slide over each other and liquids to flow. Atoms of solids, in contrast, stick together, so they cannot move apart. Differences in the weight of matter, he argued, could be explained by the closeness of atoms. Atoms of lighter matter, he thought, were more spread out and separated by more empty space. Q: Democritus thought that different kinds of atoms make up different types of matter. How is this similar to modern ideas about atoms? A: The modern view is that atoms of different elements differ in their numbers of protons and electrons and this gives them different physical and chemical properties. Dust motes dance in a beam of sunlight. | text | null |
L_0854 | democrituss idea of the atom | T_4305 | Democritus was an important philosopher, but he was less influential than another Greek philosopher named Aristo- tle, who lived about 100 years after Democritus. Aristotle rejected Democritus idea of the atom. In fact, Aristotle thought the idea was ridiculous. Unfortunately, Aristotles opinion was accepted for more than 2000 years, and Democritus idea was more or less forgotten. However, the idea of the atom was revived around 1800 by the English scientist John Dalton. Dalton developed an entire theory about the atom, much of which is still accepted today. He based his theory on experimental evidence, not on lucky guesses. | text | null |
L_0857 | descriptive statistics | T_4310 | The girls in the picture above make up a small samplethere are only four of them. In scientific investigations, samples may include hundreds or even thousands of people or other objects of study. Especially when samples are very large, its important to be able to summarize their overall characteristics with a few numbers. Thats where descriptive statistics come in. Descriptive statistics are measures that show the central tendency, or center, of a sample or the variation in a sample. | text | null |
L_0857 | descriptive statistics | T_4311 | The central tendency of a sample can be represented by the mean, median, or mode. The mean is the average value. It is calculated by adding the individual measurements and dividing the sum by the total number of measurements. The median is the middle value. To find the median, rank all the measurements from smallest to largest and then find the measurement that is in the middle. The mode is the most common value. It is the value that occurs most often. Q: A sample of five children have the following heights: 60 cm, 58 cm, 54 cm, 62 cm, and 58 cm. What are the mean, median, and mode of this sample? A: The mean is (60 cm + 58 cm + 54 cm + 62 cm + 58 cm) 5 = 58 cm. The median and mode are both 58 cm as well. The mean, median, and mode are not always the same, as they are for this sample. In fact, sometimes these three statistics are very different from one another for the same sample. | text | null |
L_0857 | descriptive statistics | T_4312 | Many samples have a lot of variation in measurements. Variation can be described with a statistic called the range. The range is the total spread of values in a sample. It is calculated by subtracting the smallest value from the largest value. Q: What is the range of heights in the sample of children in the previous question? A: The range is 62 cm - 54 cm = 8 cm. | text | null |
L_0859 | direction | T_4315 | Direction can be described in relative terms, such as up, down, in, out, left, right, forward, backward, or sideways. Direction can also be described with the cardinal directions: north, south, east, or west. On maps, cardinal directions are indicated with a compass rose. You can see one in the bottom left corner of the map in the Figure 1.1. You can use the compass rose to find directions on the map. For example, to go to the school from Jordans house, you would travel from east to west. If you wanted to go on to the post office, you would change direction at the school and then travel from south to north. | text | null |
L_0859 | direction | T_4316 | Look again at the map in the Figure 1.1. The distance from Jordans house to the post office is 3 km. But if Jordan told a friend how to reach the post office from his house, he couldnt just say go 3 kilometers. The friend might end up at the park instead of the post office. Jordan would have to include direction as well as distance. He could say, go west for 2 kilometers and then go north for 1 kilometer. | text | null |
L_0859 | direction | T_4317 | When both distance and direction are considered, motion can be represented by a vector. A vector is a measurement that has both size and direction. It may be represented by an arrow. If you are representing motion with an arrow, the length of the arrow represents distance, and the way the arrow points represents direction. The red arrows on the map in the Figure 1.1 are vectors for Jordans route from his house to the school and from the school to the post office. Q: How would you draw arrows to represent the distances and directions from the post office to the park on the map in the Figure 1.1? A: The vectors would look like this: | text | null |
L_0861 | distance | T_4322 | Distance is the length of the route between two points. The distance of a race, for example, is the length of the track between the starting and finishing lines. In a 100-meter sprint, that distance is 100 meters. | text | null |
L_0861 | distance | T_4323 | The SI unit for distance is the meter (m). Short distances may be measured in centimeters (cm), and long distances may be measured in kilometers (km). For example, you might measure the distance from the bottom to the top of a sheet of paper in centimeters and the distance from your house to your school in kilometers. | text | null |
L_0861 | distance | T_4324 | Maps can often be used to measure distance. The map in the Figure 1.1 shows the route from Jordans house to his school. You can use the scale at the bottom of the map to measure the distance between these two points. Q: What is the distance from Jordans house to his school? A: The distance is 2 kilometers. | text | null |
L_0862 | doppler effect | T_4325 | The Doppler effect is a change in the frequency of sound waves that occurs when the source of the sound waves is moving relative to a stationary listener. (It can also occur when the sound source is stationary and the listener is moving.) The Figure 1.1 shows how the Doppler effect occurs. The sound waves from the police car siren travel outward in all directions. Because the car is racing forward (to the left), the sound waves get bunched up in front of the car and spread out behind it. Sound waves that are closer together have a higher frequency, and sound waves that are farther apart have a lower frequency. The frequency of sound waves, in turn, determines the pitch of the sound. Sound waves with a higher frequency produce sound with a higher pitch, and sound waves with a lower frequency produce sound with a lower pitch. | text | null |
L_0862 | doppler effect | T_4326 | As the car approaches listener A, the sound waves get closer together, increasing their frequency. This listener hears the pitch of the siren get higher. As the car speeds away from listener B, the sound waves get farther apart, decreasing their frequency. This listener hears the pitch of the siren get lower. Q: What will the siren sound like to listener A after the police car passes him? A: The siren will suddenly get lower in pitch because the sound waves will be much more spread out and have a lower frequency. | text | null |
L_0863 | earth as a magnet | T_4327 | Imagine a huge bar magnet passing through Earths axis, as in the Figure 1.1. This is a good representation of Earth as a magnet. Like a bar magnet, Earth has north and south magnetic poles. A magnetic pole is the north or south end of a magnet, where the magnet exerts the most force. | text | null |
L_0863 | earth as a magnet | T_4328 | Although the needle of a compass always points north, it doesnt point to Earths north geographic pole. Find the north geographic pole in the Figure 1.2. As you can see, it is located at 90 north latitude. Where does a compass Q: The north end of a compass needle points toward Earths north magnetic pole. The like poles of two magnets repel each other, and the opposite poles attract. So why doesnt the north end of a compass needle point to Earths south magnetic pole instead? A: The answer may surprise you. The compass needle actually does point to the south pole of magnet Earth. However, it is called the north magnetic pole because it is close to the north geographic pole. This naming convention was adopted a long time ago to avoid confusion. | text | null |
L_0863 | earth as a magnet | T_4328 | Although the needle of a compass always points north, it doesnt point to Earths north geographic pole. Find the north geographic pole in the Figure 1.2. As you can see, it is located at 90 north latitude. Where does a compass Q: The north end of a compass needle points toward Earths north magnetic pole. The like poles of two magnets repel each other, and the opposite poles attract. So why doesnt the north end of a compass needle point to Earths south magnetic pole instead? A: The answer may surprise you. The compass needle actually does point to the south pole of magnet Earth. However, it is called the north magnetic pole because it is close to the north geographic pole. This naming convention was adopted a long time ago to avoid confusion. | text | null |
L_0863 | earth as a magnet | T_4329 | Like all magnets, Earth has a magnetic field. Earths magnetic field is called the magnetosphere. You can see a model of the magnetosphere in the Figure 1.3. It is a huge region that extends outward from Earth in all directions. Earth exerts magnetic force over the entire field, but the force is strongest at the poles, where lines of force converge. Click image to the left or use the URL below. URL: | text | null |
L_0864 | efficiency | T_4330 | A dolly is a machine because it changes a force to make work easier. What is work? In physics, work is defined as the use of force to move an object over a distance. It is represented by the equation: Work = Force x Distance All machines make work easier, but they dont increase the amount of work that is done. You can never get more work out of a machine than you put into it. In fact, a machine always does less work on an object than the user does on the machine. Thats because a machine must use some of the work put into it to overcome friction. Friction is the force that opposes motion between any surfaces that are touching. All machines involve motion, so they all have friction. How much work is needed to overcome friction in a machine depends on the machines efficiency. | text | null |
L_0864 | efficiency | T_4331 | Efficiency is the percent of work put into a machine by the user (input work) that becomes work done by the machine (output work). The output work is always less than the input work because some of the input work is used to overcome friction. Therefore, efficiency is always less than 100 percent. The closer to 100 percent a machines efficiency is, the better it is at reducing friction. Look at the ramp in the Figure 1.1. A ramp is a type of simple machine called an inclined plane. It is easier to push the heavy piece of furniture up the ramp to the truck than to lift it straight up off the ground, but pushing the furniture over the surface of the ramp creates a lot of friction. Some of the force applied to moving the furniture must be used to overcome the friction with the ramp. Q: Why would it be more efficient to use a dolly to roll the furniture up the ramp? A: There would be less friction to overcome if you used a dolly because of the wheels. So the efficiency of the ramp would be greater with the dolly. | text | null |
L_0864 | efficiency | T_4332 | Efficiency can be calculated with the equation: Output work Efficiency = Input work 100% Consider a machine that puts out 6000 joules of work. To produce that much work from the machine requires the user to put in 8000 joules of work. To find the efficiency of the machine, substitute these values into the equation for efficiency: 6000 J 100% = 75% 8000 J Q: Rani puts 7500 joules of work into pushing a box up a ramp, but only 6700 joules of work actually go into moving the box. The rest of the work overcomes friction between the box and the ramp. What is the efficiency of the ramp? A: The efficiency of the ramp is: 6700 J 100% = 90% 7500 J | text | null |
L_0865 | einsteins concept of gravity | T_4333 | In the late 1600s, Isaac Newton introduced his law of gravity, which identifies gravity as a force of attraction between all objects with mass in the universe. The law also states that the strength of gravity between two objects depends on their mass and distance apart. Newtons law of gravity was accepted for more than two centuries. It can predict the motion of most objects and was even used by NASA to land astronauts on the moon. Its still used for most practical purposes. However, Newtons law doesnt explain why gravity occurs. It only describes how gravity seems to affect objects. There are also some cases in which Newtons law doesnt even describe what happens. Q: Newton expressed his ideas about gravity as a law. A law in science is a description of what always occurs in nature. For example, according to Newtons law, objects on Earth always fall down, not up. What is needed to explain gravity? A: A theory is needed to explain gravity. In science, a theory is a broad explanation that is supported by a great deal of evidence. | text | null |
L_0865 | einsteins concept of gravity | T_4334 | In the early 1900s, Albert Einstein came up with a theory of gravity that actually explains gravity rather than simply describing its effects. Einstein showed mathematically that gravity is not really a force that of attraction between all objects with mass, as Newton thought. Instead, Einstein showed that gravity is a result of the warping, or curving, of space and time, which made up the same space-time fabric. These ideas about space-time and gravity became known as Einsteins theory of general relativity. | text | null |
L_0865 | einsteins concept of gravity | T_4335 | Einstein derived his theory using mathematics. However, you can get a good grasp of it with the help of a simple visual analogy. Imagine a bowling ball pressing down on a trampoline. The surface of the trampoline would curve downward instead of being flat. Now imagine placing a lighter ball at the edge of the trampoline. What will happen? It will roll down toward the bowling ball. This apparent attraction to the bowling ball occurs because the trampoline curves downward, not because the two balls are actually attracted to one another by an invisible force called gravity. Einstein theorized that the sun and other very massive bodies affect space and time around them in a way that is similar to the effect of the bowling ball on the trampoline. The more massive a body is, the more it causes space-time to curve. This idea is represented by the Figure 1.1. According to Einstein, objects move toward one another because of the curves in space-time, not because they are pulling on each other with a force of attraction. Einsteins theory is supported by evidence and widely accepted today, although Newtons law is still used for many calculations. | text | null |
L_0866 | elastic force | T_4336 | Something that is elastic can return to its original shape after being stretched or compressed. This property is called elasticity. As you stretch or compress an elastic material like a bungee cord, it resists the change in shape. It exerts a counter force in the opposite direction. This force is called elastic force. The farther the material is stretched or compressed, the greater the elastic force becomes. As soon as the stretching or compressing force is released, elastic force causes the material to spring back to its original shape. Click image to the left or use the URL below. URL: Q: What force stretches the bungee cord after the jumper jumps? When does the bungee cord snap back to its original shape? A: After the bungee jumper jumps, he accelerates toward the ground due to gravity. His weight stretches the bungee cord. As the bungee cord stretches, it exerts elastic force upward against the jumper, which slows his descent and brings him to a momentary stop. Then the bungee cord springs back to its original shape, and the jumper bounces upward. | text | null |
L_0866 | elastic force | T_4337 | Elastic force can be very useful and not just for bungee jumping. In fact, you probably use elastic force every day. A few common uses of elastic force are shown in the Figure 1.1. Do you use elastic force in any of these ways? Q: How does the resistance band work? How does it use elastic force? A: When you pull on the band, it stretches but doesnt break. The resistance you feel when you pull on it is elastic force. The farther you stretch the band, the greater the resistance is. The resistance of the band to stretching is what gives your muscles a workout. After you stop pulling on the band, it returns to its original shape, ready for the next stretch. Springs like the spring toy pictured in the Figure 1.2 also have elastic force when they are stretched or compressed. Q: Can you think of other uses of springs? A: Bedsprings provide springy support beneath a mattress. The spring in a door closer pulls the door shut. The spring in a retractable ballpoint pen retracts the point of the pen. The spring in a pogo stick bounces the rider up off the ground. | text | null |
L_0866 | elastic force | T_4337 | Elastic force can be very useful and not just for bungee jumping. In fact, you probably use elastic force every day. A few common uses of elastic force are shown in the Figure 1.1. Do you use elastic force in any of these ways? Q: How does the resistance band work? How does it use elastic force? A: When you pull on the band, it stretches but doesnt break. The resistance you feel when you pull on it is elastic force. The farther you stretch the band, the greater the resistance is. The resistance of the band to stretching is what gives your muscles a workout. After you stop pulling on the band, it returns to its original shape, ready for the next stretch. Springs like the spring toy pictured in the Figure 1.2 also have elastic force when they are stretched or compressed. Q: Can you think of other uses of springs? A: Bedsprings provide springy support beneath a mattress. The spring in a door closer pulls the door shut. The spring in a retractable ballpoint pen retracts the point of the pen. The spring in a pogo stick bounces the rider up off the ground. | text | null |
L_0881 | electromagnetic spectrum | T_4379 | Electromagnetic radiation is energy that travels in waves across space as well as through matter. Most of the electromagnetic radiation on Earth comes from the sun. Like other waves, electromagnetic waves are characterized by certain wavelengths and wave frequencies. Wavelength is the distance between two corresponding points on adjacent waves. Wave frequency is the number of waves that pass a fixed point in a given amount of time. Electromagnetic waves with shorter wavelengths have higher frequencies and more energy. | text | null |
L_0881 | electromagnetic spectrum | T_4380 | Visible light and infrared light are just a small part of the full range of electromagnetic radiation, which is called the electromagnetic spectrum. You can see the waves of the electromagnetic spectrum in the Figure 1.1. At the top of the diagram, the wavelengths of the waves are given. Also included are objects that are about the same size as the corresponding wavelengths. The frequencies and energy levels of the waves are shown at the bottom of the diagram. Some sources of the waves are also given. On the left side of the electromagnetic spectrum diagram are radio waves and microwaves. Radio waves have the longest wavelengths and lowest frequencies of all electromagnetic waves. They also have the least amount of energy. On the right side of the diagram are X rays and gamma rays. They have the shortest wavelengths and highest frequencies of all electromagnetic waves. They also have the most energy. Between these two extremes are waves that are commonly called light. Light includes infrared light, visible light, and ultraviolet light. The wavelengths, frequencies, and energy levels of light fall in between those of radio waves on the left and X rays and gamma rays on the right. Q: Which type of light has the longest wavelengths? A: Infrared light has the longest wavelengths. Q: What sources of infrared light are shown in the diagram? A: The sources in the diagram are people and light bulbs, but all living things and most other objects give off infrared light. | text | null |
L_0882 | electromagnetic waves | T_4381 | Electromagnetic waves are waves that consist of vibrating electric and magnetic fields. Like other waves, electro- magnetic waves transfer energy from one place to another. The transfer of energy by electromagnetic waves is called electromagnetic radiation. Electromagnetic waves can transfer energy through matter or across empty space. Click image to the left or use the URL below. URL: Q: How do microwaves transfer energy inside a microwave oven? A: They transfer energy through the air inside the oven to the food. | text | null |
L_0882 | electromagnetic waves | T_4382 | A familiar example may help you understand the vibrating electric and magnetic fields that make up electromagnetic waves. Consider a bar magnet, like the one in the Figure 1.1. The magnet exerts magnetic force over an area all around it. This area is called a magnetic field. The field lines in the diagram represent the direction and location of the magnetic force. Because of the field surrounding a magnet, it can exert force on objects without touching them. They just have to be within its magnetic field. Q: How could you demonstrate that a magnet can exert force on objects without touching them? A: You could put small objects containing iron, such as paper clips, near a magnet and show that they move toward the magnet. An electric field is similar to a magnetic field. It is an area of electrical force surrounding a positively or negatively charged particle. You can see electric fields in the following Figure 1.2. Like a magnetic field, an electric field can exert force on objects over a distance without actually touching them. | text | null |
L_0882 | electromagnetic waves | T_4383 | An electromagnetic wave begins when an electrically charged particle vibrates. The Figure 1.3 shows how this happens. A vibrating charged particle causes the electric field surrounding it to vibrate as well. A vibrating electric field, in turn, creates a vibrating magnetic field. The two types of vibrating fields combine to create an electromagnetic wave. | text | null |
L_0882 | electromagnetic waves | T_4383 | An electromagnetic wave begins when an electrically charged particle vibrates. The Figure 1.3 shows how this happens. A vibrating charged particle causes the electric field surrounding it to vibrate as well. A vibrating electric field, in turn, creates a vibrating magnetic field. The two types of vibrating fields combine to create an electromagnetic wave. | text | null |
L_0882 | electromagnetic waves | T_4384 | As you can see in the Figure 1.3, the electric and magnetic fields that make up an electromagnetic wave are perpendicular (at right angles) to each other. Both fields are also perpendicular to the direction that the wave travels. Therefore, an electromagnetic wave is a transverse wave. However, unlike a mechanical transverse wave, which can only travel through matter, an electromagnetic transverse wave can travel through empty space. When waves travel through matter, they lose some energy to the matter as they pass through it. But when waves travel through space, no energy is lost. Therefore, electromagnetic waves dont get weaker as they travel. However, the energy is diluted as it travels farther from its source because it spreads out over an ever-larger area. | text | null |
L_0882 | electromagnetic waves | T_4385 | When electromagnetic waves strike matter, they may interact with it in the same ways that mechanical waves interact with matter. Electromagnetic waves may: reflect, or bounce back from a surface; refract, or bend when entering a new medium; diffract, or spread out around obstacles. Electromagnetic waves may also be absorbed by matter and converted to other forms of energy. Microwaves are a familiar example. When microwaves strike food in a microwave oven, they are absorbed and converted to thermal energy, which heats the food. | text | null |
L_0882 | electromagnetic waves | T_4386 | The most important source of electromagnetic waves on Earth is the sun. Electromagnetic waves travel from the sun to Earth across space and provide virtually all the energy that supports life on our planet. Many other sources of electromagnetic waves depend on technology. Radio waves, microwaves, and X rays are examples. We use these electromagnetic waves for communications, cooking, medicine, and many other purposes. | text | null |
L_0884 | electron cloud atomic model | T_4390 | Up until about 1920, scientists accepted Niels Bohrs model of the atom. In this model, negative electrons circle the positive nucleus at fixed distances from the nucleus, called energy levels. You can see the model in Figure 1.1 for an atom of the element nitrogen. Bohrs model is useful for understanding properties of elements and their chemical interactions. However, it doesnt explain certain behaviors of electrons, except for those in the simplest atom, the hydrogen atom. | text | null |
L_0884 | electron cloud atomic model | T_4391 | In the mid-1920s, an Austrian scientist named Erwin Schrdinger thought that the problem with Bohrs model was restricting the electrons to specific orbits. He wondered if electrons might behave like light, which scientists already knew had properties of both particles and waves. Schrdinger speculated that electrons might also travel in waves. Q: How do you pin down the location of an electron in a wave? A: You cant specify the exact location of an electron. However, Schrdinger showed that you can at least determine where an electron is most likely to be. Schrdinger developed an equation that could be used to calculate the chances of an electron being in any given place around the nucleus. Based on his calculations, he identified regions around the nucleus where electrons are most likely to be. He called these regions orbitals. As you can see in the Figure 1.2, orbitals may be shaped like spheres, dumbbells, or rings. In each case, the nucleus of the atom is at the center of the orbital. | text | null |
L_0884 | electron cloud atomic model | T_4391 | In the mid-1920s, an Austrian scientist named Erwin Schrdinger thought that the problem with Bohrs model was restricting the electrons to specific orbits. He wondered if electrons might behave like light, which scientists already knew had properties of both particles and waves. Schrdinger speculated that electrons might also travel in waves. Q: How do you pin down the location of an electron in a wave? A: You cant specify the exact location of an electron. However, Schrdinger showed that you can at least determine where an electron is most likely to be. Schrdinger developed an equation that could be used to calculate the chances of an electron being in any given place around the nucleus. Based on his calculations, he identified regions around the nucleus where electrons are most likely to be. He called these regions orbitals. As you can see in the Figure 1.2, orbitals may be shaped like spheres, dumbbells, or rings. In each case, the nucleus of the atom is at the center of the orbital. | text | null |
L_0884 | electron cloud atomic model | T_4392 | Schrdingers work on orbitals is the basis of the modern model of the atom, which scientists call the quantum mechanical model. The modern model is also commonly called the electron cloud model. Thats because each orbital around the nucleus of the atom resembles a fuzzy cloud around the nucleus, like the ones shown in the Figure 1.3 for a helium atom. The densest area of the cloud is where the electrons have the greatest chances of being. Q: In the model pictured in the Figure 1.3, where are the two helium electrons most likely to be? A: The two electrons are most likely to be inside the sphere closest to the nucleus where the cloud is darkest. | text | null |
L_0888 | electrons | T_4403 | Electrons are one of three main types of particles that make up atoms. The other two types are protons and neutrons. Unlike protons and neutrons, which consist of smaller, simpler particles, electrons are fundamental particles that do not consist of smaller particles. They are a type of fundamental particles called leptons. All leptons have an electric charge of -1 or 0. Click image to the left or use the URL below. URL: | text | null |
L_0888 | electrons | T_4404 | Electrons are extremely small. The mass of an electron is only about 1/2000 the mass of a proton or neutron, so electrons contribute virtually nothing to the total mass of an atom. Electrons have an electric charge of -1, which is equal but opposite to the charge of proton, which is +1. All atoms have the same number of electrons as protons, so the positive and negative charges cancel out, making atoms electrically neutral. | text | null |
L_0888 | electrons | T_4405 | Unlike protons and neutrons, which are located inside the nucleus at the center of the atom, electrons are found outside the nucleus. Because opposite electric charges attract each other, negative electrons are attracted to the positive nucleus. This force of attraction keeps electrons constantly moving through the otherwise empty space around the nucleus. The Figure shown 1.1 is a common way to represent the structure of an atom. It shows the electron as a particle orbiting the nucleus, similar to the way that planets orbit the sun. | text | null |
L_0888 | electrons | T_4406 | The atomic model above is useful for some purposes, but its too simple when it comes to the location of electrons. In reality, its impossible to say what path an electron will follow. Instead, its only possible to describe the chances of finding an electron in a certain region around the nucleus. The region where an electron is most likely to be is called an orbital. Each orbital can have at most two electrons. Some orbitals, called S orbitals, are shaped like spheres, with the nucleus in the center. An S orbital is pictured in Figure 1.2. Where the dots are denser, the chance of finding an electron is greater. Also pictured in Figure 1.2 is a P orbital. P orbitals are shaped like dumbbells, with the nucleus in the pinched part of the dumbbell. Click image to the left or use the URL below. URL: Q: How many electrons can there be in each type of orbital shown above? A: There can be a maximum of two electrons in any orbital, regardless of its shape. Q: Where is the nucleus in each orbital? A: The nucleus is at the center of each orbital. It is in the middle of the sphere in the S orbital and in the pinched part of the P orbital. | text | null |
L_0888 | electrons | T_4407 | Electrons are located at fixed distances from the nucleus, called energy levels. You can see the first three energy levels in the Figure 1.3. The diagram also shows the maximum possible number of electrons at each energy level. Electrons at lower energy levels, which are closer to the nucleus, have less energy. At the lowest energy level, which has the least energy, there is just one orbital, so this energy level has a maximum of two electrons. Only when a lower energy level is full are electrons added to the next higher energy level. Electrons at higher energy levels, which are farther from the nucleus, have more energy. They also have more orbitals and greater possible numbers of electrons. Electrons at the outermost energy level of an atom are called valence electrons. They determine many of the properties of an element. Thats because these electrons are involved in chemical reactions with other atoms. Atoms may share or transfer valence electrons. Shared electrons bind atoms together to form chemical compounds. Q: If an atom has 12 electrons, how will they be distributed in energy levels? A: The atom will have two electrons at the first energy level, eight at the second energy level, and the remaining two at the third energy level. Q: Sometimes, an electron jumps from one energy level to another. How do you think this happens? A: To change energy levels, an electron must either gain or lose energy. Thats because electrons at higher energy levels have more energy than electrons at lower energy levels. | text | null |
L_0889 | elements | T_4408 | A pure substance is called an element. An element is a pure substance because it cannot be separated into any other substances. Currently, 92 different elements are known to exist in nature, although additional elements have been formed in labs. All matter consists of one or more of these elements. Some elements are very common; others are relatively rare. The most common element in the universe is hydrogen, which is part of Earths atmosphere and a component of water. The most common element in Earths atmosphere is nitrogen, and the most common element in Earths crust is oxygen. Click image to the left or use the URL below. URL: | text | null |
L_0889 | elements | T_4409 | Each element has a unique set of properties that is different from the set of properties of any other element. For example, the element iron is a solid that is attracted by a magnet and can be made into a magnet, like the compass needle shown in the Figure 1.1. The element neon, on the other hand, is a gas that gives off a red glow when electricity flows through it. The lighted sign in the Figure 1.2 contains neon. The needle of this compass is made of the element iron. Q: Do you know properties of any other elements? For example, what do you know about helium? A: Helium is a gas that has a lower density than air. Thats why helium balloons have to be weighted down so they wont float away. Q: Living things, like all matter, are made of elements. Do you know which element is most common in living things? A: Carbon is the most common element in living things. It has the unique property of being able to combine with many other elements as well as with itself. This allows carbon to form a huge number of different substances. | text | null |
L_0889 | elements | T_4410 | For thousands of years, people have wondered about the substances that make up matter. About 2500 years ago, the Greek philosopher Aristotle argued that all matter is made up of just four elements, which he identified as earth, air, water, and fire. He thought that different substances vary in their properties because they contain different proportions of these four elements. Aristotle had the right idea, but he was wrong about which substances are elements. Nonetheless, his four elements were accepted until just a few hundred years ago. Then scientists started discovering many of the elements with which we are familiar today. Eventually they discovered dozens of different elements. | text | null |
L_0889 | elements | T_4411 | The smallest particle of an element that still has the properties of that element is the atom. Atoms actually consist of smaller particles, including protons and electrons, but these smaller particles are the same for all elements. All the atoms of an element are like one another, and are different from the atoms of all other elements. For example, the atoms of each element have a unique number of protons. Consider carbon as an example. Carbon atoms have six protons. They also have six electrons. All carbon atoms are the same whether they are found in a lump of coal or a teaspoon of table sugar (Figure 1.3). On the other hand, carbon atoms are different from the atoms of hydrogen, which are also found in coal and sugar. Each hydrogen atom has just one proton and one electron. Carbon is the main element in coal (left). Carbon is also a major component of sugar (right). Q: Why do you think coal and sugar are so different from one another when carbon is a major component of each A: Coal and sugar differ from one another because they contain different proportions of carbon and other elements. For example, coal is about 85 percent carbon, whereas table sugar is about 42 percent carbon. Both coal and sugar also contain the elements hydrogen and oxygen but in different proportions. In addition, coal contains the elements nitrogen and sulfur. | text | null |
L_0890 | endothermic reactions | T_4412 | All chemical reactions involve energy. Energy is used to break bonds in reactants, and energy is released when new bonds form in products. In some chemical reactions, called exothermic reactions, more energy is released when new bonds form in the products than is needed to break bonds in the reactants. The opposite is true of endothermic reactions. In an endothermic reaction, it takes more energy to break bonds in the reactants than is released when new bonds form in the products. | text | null |
L_0890 | endothermic reactions | T_4413 | The word endothermic literally means taking in heat. A constant input of energy, often in the form of heat, is needed to keep an endothermic reaction going. This is illustrated in the Figure 1.1. Energy must be constantly added because not enough energy is released when the products form to break more bonds in the reactants. The general equation for an endothermic reaction is: Reactants + Energy Products Note: H represents the change in en- ergy. In endothermic reactions, the temperature of the products is typically lower than the temperature of the reactants. The drop in temperature may be great enough to cause liquids to freeze. Q: Now can you guess how an instant cold pack works? A: Squeezing the cold pack breaks an inner bag of water, and the water mixes with a chemical inside the pack. The chemical and water combine in an endothermic reaction. The energy needed for the reaction to take place comes from the water, which gets colder as the reaction proceeds. | text | null |
L_0890 | endothermic reactions | T_4414 | One of the most important series of endothermic reactions is photosynthesis. In photosynthesis, plants make the simple sugar glucose (C6 H12 O6 ) from carbon dioxide (CO2 ) and water (H2 O). They also release oxygen (O2 ) in the process. The reactions of photosynthesis are summed up by this chemical equation: 6 CO2 + 6 H2 O C6 H12 O6 + 6 O2 The energy for photosynthesis comes from light. Without light energy, photosynthesis cannot occur. As you can see in the Figure 1.2, plants can get the energy they need for photosynthesis from either sunlight or artificial light. | text | null |
L_0891 | energy | T_4415 | Energy is defined in science as the ability to move matter or change matter in some other way. Energy can also be defined as the ability to do work, which means using force to move an object over a distance. When work is done, energy is transferred from one object to another. For example, when the boy in the Figure 1.1 uses force to swing the racket, he transfers some of his energy to the racket. Q: It takes energy to play tennis. Where does this boy get his energy? A: He gets energy from the food he eats. | text | null |
L_0891 | energy | T_4416 | Because energy is the ability to do work, it is expressed in the same unit that is used for work. The SI unit for both work and energy is the joule (J), or Newton meter (N m). One joule is the amount of energy needed to apply a force of 1 Newton over a distance of 1 meter. For example, suppose the boy in the Figure 1.1 applies 20 Newtons of force to his tennis racket over a distance of 1 meter. The energy needed to do this work is 20 N m, or 20 J. | text | null |
L_0891 | energy | T_4417 | If you think about different sources of energysuch as batteries and the sunyou probably realize that energy can take different forms. For example, when the boy swings his tennis racket, the energy of the moving racket is an example of mechanical energy. To move his racket, the boy needs energy stored in food, which is an example of chemical energy. Other forms of energy include electrical, thermal, light, and sound energy. The different forms of energy can also be classified as either kinetic energy or potential energy. Kinetic energy is the energy of moving matter. Potential energy is energy that is stored in matter. Q: Is the chemical energy in food kinetic energy or potential energy? A: The chemical energy in food is potential energy. It is stored in the chemical bonds that make up food molecules. The stored energy is released when we digest food. Then we can use it for many purposes, such as moving (mechanical energy) or staying warm (thermal energy). Q: What is an example of kinetic energy? A: Anything that is moving has kinetic energy. An example is a moving tennis racket. | text | null |
L_0892 | energy conversion | T_4418 | Gravity is a force, but not like other forces you may know. Gravity is a bit special. You know that a force is a push or pull. If you push a ball, it starts to roll. If you lift a book, it moves upward. Now, imagine you drop a ball. It falls to the ground. Can you see the force pulling it down? That is what makes gravity really cool. It is invisible. Invisible means you cannot see it. But wait, it has even more surprises. Gravity holds planets in place around the Sun. Gravity keeps the Moon from flying off into space. Gravity exerts a force on objects that are not even touching. In fact, gravity can act over very large distances. However, the force does get weaker the farther apart the objects are. | text | null |
L_0892 | energy conversion | T_4419 | You are already very familiar with Earths gravity. It constantly pulls you toward Earths center. What might happen if there was no gravity? You know that the Earth is rotating on its axis. This motion causes our day and night cycle. The Earth also orbits the Sun. All this motion may cause you to fly off the Earth! You can thank gravity for keeping you in place. Gravity keeps us firmly down on the ground. Gravity also pulls on objects that are in the sky. It also pulls on objects that are in space. Meteors and skydivers are pulled down by gravity. Gravity also keeps the moon orbiting the Earth. Without gravity, the moon would float away. It also holds artificial satellites in their orbit. Many of these satellites help to connect the world. They allow you to pick up a phone a call in many parts of the world. You can also thank gravity for all your TV channels. Gravity keeps Earth and the other planets moving around the much more massive Sun. | text | null |
L_0892 | energy conversion | T_4420 | "What goes up must come down." You have probably heard that statement before. At one time this statement was true, but no longer. Since the 1960s, we have sent many spacecraft into space. Some are still traveling away from Earth. So it is possible to overcome gravity. Do you need a giant rocket to overcome gravity? No, you actually overcome gravity every day. Think about when you climb a set of stairs. When you do, you are overcoming gravity. What if you jump on a trampoline? You are overcoming gravity for a few seconds. Everyone can overcome gravity. You just need to apply a force larger than gravity. Think about that the next time you jump into the air. You are overcoming gravity for a brief second. Enjoy it while it lasts. Eventually, gravity will win the battle. | text | null |
L_0892 | energy conversion | T_4421 | 1. What is the traditional definition of gravity? 2. Identify factors that influence the strength of gravity between two objects. | text | null |
L_0892 | energy conversion | T_4422 | By clicking a link below, you will leave the CK-12 site and open an external site in a new tab. This page will remain open in the original tab. | text | null |
L_0893 | energy level | T_4423 | Energy levels (also called electron shells) are fixed distances from the nucleus of an atom where electrons may be found. Electrons are tiny, negatively charged particles in an atom that move around the positive nucleus at the center. Energy levels are a little like the steps of a staircase. You can stand on one step or another but not in between the steps. The same goes for electrons. They can occupy one energy level or another but not the space between energy levels. The model in the Figure 1.1 shows the first four energy levels of an atom. Electrons in energy level I (also called energy level K) have the least amount of energy. As you go farther from the nucleus, electrons at higher levels have more energy, and their energy increases by a fixed, discrete amount. Electrons can jump from a lower to the next higher energy level if they absorb this amount of energy. Conversely, if electrons jump from a higher to a lower energy level, they give off energy, often in the form of light. This explains the fireworks pictured above. When the fireworks explode, electrons gain energy and jump to higher energy levels. When they jump back to their original energy levels, they release the energy as light. Different atoms have different arrangements of electrons, so they give off light of different colors. Q: In the atomic model Figure 1.1, where would you find electrons that have the most energy? A: Electrons with the most energy would be found in energy level IV. | text | null |
L_0893 | energy level | T_4424 | The smallest atoms are hydrogen atoms. They have just one electron orbiting the nucleus. That one electron is in the first energy level. Bigger atoms have more electrons. Electrons are always added to the lowest energy level first until it has the maximum number of electrons possible. Then electrons are added to the next higher energy level until that level is full, and so on. How many electrons can a given energy level hold? The maximum numbers of electrons possible for the first four energy levels are shown in the Figure 1.1. For example, energy level I can hold a maximum of two electrons, and energy level II can hold a maximum of eight electrons. The maximum number depends on the number of orbitals at a given energy level. An orbital is a volume of space within an atom where an electron is most likely to be found. As you can see by the images in the Figure 1.2, some orbitals are shaped like spheres (S orbitals) and some are shaped like dumbbells (P orbitals). There are other types of orbitals as well. Regardless of its shape, each orbital can hold a maximum of two electrons. Energy level I has just one orbital, so two electrons will fill this energy level. Energy level II has four orbitals, so it takes eight electrons to fill this energy level. Q: Energy level III can hold a maximum of 18 electrons. How many orbitals does this energy level have? A: At two electrons per orbital, this energy level must have nine orbitals. | text | null |
L_0893 | energy level | T_4425 | Electrons in the outermost energy level of an atom have a special significance. These electrons are called valence electrons, and they determine many of the properties of an atom. An atom is most stable if its outermost energy level contains as many electrons as it can hold. For example, helium has two electrons, both in the first energy level. This energy level can hold only two electrons, so heliums only energy level is full. This makes helium a very stable element. In other words, its atoms are unlikely to react with other atoms. Consider the elements fluorine and lithium, modeled in the Figure 1.3. Fluorine has seven of eight possible electrons in its outermost energy level, which is energy level II. It would be more stable if it had one more electron because this would fill its outermost energy level. Lithium, on the other hand, has just one of eight possible electrons in its outermost energy level (also energy level II). It would be more stable if it had one less electron because it would have a full outer energy level (now energy level I). Both fluorine and lithium are highly reactive elements because of their number of valence electrons. Fluorine will readily gain one electron and lithium will just as readily give up one electron to become more stable. In fact, lithium and fluorine will react together as shown in the Figure 1.4. When the two elements react, lithium transfers its one extra electron to fluorine. Q: A neon atom has ten electrons. How many electrons does it have in its outermost energy level? How stable do you think a neon atom is? A: A neon atom has two electrons in energy level I and its remaining eight electrons in energy level II, which can | text | null |
L_0893 | energy level | T_4425 | Electrons in the outermost energy level of an atom have a special significance. These electrons are called valence electrons, and they determine many of the properties of an atom. An atom is most stable if its outermost energy level contains as many electrons as it can hold. For example, helium has two electrons, both in the first energy level. This energy level can hold only two electrons, so heliums only energy level is full. This makes helium a very stable element. In other words, its atoms are unlikely to react with other atoms. Consider the elements fluorine and lithium, modeled in the Figure 1.3. Fluorine has seven of eight possible electrons in its outermost energy level, which is energy level II. It would be more stable if it had one more electron because this would fill its outermost energy level. Lithium, on the other hand, has just one of eight possible electrons in its outermost energy level (also energy level II). It would be more stable if it had one less electron because it would have a full outer energy level (now energy level I). Both fluorine and lithium are highly reactive elements because of their number of valence electrons. Fluorine will readily gain one electron and lithium will just as readily give up one electron to become more stable. In fact, lithium and fluorine will react together as shown in the Figure 1.4. When the two elements react, lithium transfers its one extra electron to fluorine. Q: A neon atom has ten electrons. How many electrons does it have in its outermost energy level? How stable do you think a neon atom is? A: A neon atom has two electrons in energy level I and its remaining eight electrons in energy level II, which can | text | null |
L_0894 | enzymes as catalysts | T_4426 | Chemical reactions constantly occur inside the cells of living things. However, under the conditions inside cells, most biochemical reactions would occur too slowly to maintain life. Thats where enzymes come in. Enzymes are catalysts in living things. Like other catalysts, they speed up chemical reactions. Enzymes are proteins that are synthesized in the cells that need them, based on instructions encoded in the cells DNA. | text | null |
L_0894 | enzymes as catalysts | T_4427 | Enzymes increase the rate of chemical reactions by reducing the amount of activation energy needed for reactants to start reacting. One way this can happen is modeled in the Figure 1.1. Enzymes arent changed or used up in the reactions they catalyze, so they can be used to speed up the same reaction over and over again. Each enzyme is highly specific for the particular reaction is catalyzes, so enzymes are very effective. A reaction that would take many years to occur without its enzyme might occur in a split second with the enzyme. Enzymes are also very efficient, so waste products rarely form. Q: This model of enzyme action is called the lock-and-key model. Explain why. A: The substrates (reactants) fit precisely into the active site of the enzyme like a key into a lock. Being brought together in the enzyme in this way helps the reactants react more easily. After the product is formed, it is released by the enzyme. The enzyme is now ready to pick up more reactants and catalyze another reaction. Click image to the left or use the URL below. URL: | text | null |
L_0894 | enzymes as catalysts | T_4428 | More than 1000 different enzymes are necessary for human life. Many enzymes are needed for the digestion of food. Two examples are amylase and pepsin. Both are described in the Figure 1.2. | text | null |
L_0897 | exothermic reactions | T_4435 | All chemical reactions involve energy. Energy is used to break bonds in reactants, and energy is released when new bonds form in products. In some chemical reactions, called endothermic reactions, less energy is released when new bonds form in the products than is needed to break bonds in the reactants. The opposite is true of exothermic reactions. In an exothermic reaction, it takes less energy to break bonds in the reactants than is released when new bonds form in the products. | text | null |
L_0897 | exothermic reactions | T_4436 | The word exothermic means releasing heat. Energy, often in the form of heat, is released as an exothermic reaction proceeds. This is illustrated in the Figure 1.1. The general equation for an exothermic reaction is: Reactants Products + Energy If the energy produced in an exothermic reaction is released as heat, it results in a rise in temperature. As a result, the products are likely to be warmer than the reactants. Note: H represents the change in en- ergy. Q: You turn on the hot water faucet, and hot water pours out. How does the water get hot? Do you think that an exothermic reaction might be involved? A: A hot water heater increases the temperature of water in most homes. Many hot water heaters burn a fuel such as natural gas. The burning fuel causes the water to get hot because combustion is an exothermic reaction. | text | null |
L_0897 | exothermic reactions | T_4437 | All combustion reactions are exothermic reactions. During a combustion reaction, a substance burns as it combines with oxygen. When substances burn, they usually give off energy as heat and light. Look at the big bonfire in the Figure 1.2. The combustion of wood is an exothermic reaction that releases a lot of energy as heat and light. You can see the light energy the fire is giving off. If you were standing near the fire, you would also feel its heat. | text | null |
L_0898 | external combustion engines | T_4438 | A combustion engine is a complex machine that burns fuel to produce thermal energy and then uses the thermal energy to do work. There are two types of combustion engines: external and internal. A steam engine is an external combustion engine. | text | null |
L_0898 | external combustion engines | T_4439 | An external combustion engine burns fuel externally, or outside the engine. The burning fuel releases thermal energy, which is used to heat water and change it to steam. The pressure of the steam moves a piston back and forth inside a cylinder. The kinetic energy of the moving piston can be used to turn a vehicles wheels, a turbine, or other mechanical device. The Figure 1.1 explains in greater detail how this type of engine works. Q: What type of energy does the piston have when it moves back and forth inside the cylinder? A: Like anything else that is moving, the moving piston has kinetic energy. | text | null |
L_0899 | ferromagnetic material | T_4440 | Magnetism is the ability of a material to be attracted by a magnet and to act as a magnet. Magnetism is due to the movement of electrons within atoms of matter. When electrons spin around the nucleus of an atom, it causes the atom to become a tiny magnet, with north and south poles and a magnetic field. In most materials, the north and south poles of atoms point in all different directions, so overall the material is not magnetic. Examples of nonmagnetic materials include wood, glass, plastic, paper, copper, and aluminum. These materials are not attracted to magnets and cannot become magnets. In other materials, there are regions where the north and south poles of atoms are all lined up in the same direction. These regions are called magnetic domains. Generally, the magnetic domains point in different directions, so the material is still not magnetic. However, the material can be magnetized (made into a magnet) by placing it in a magnetic field. When this happens, all the magnetic domains line up, and the material becomes a magnet. You can see this in the Figure 1.1. Materials that can be magnitized are called ferromagnetic materials. They include iron, cobalt, and nickel. | text | null |
L_0899 | ferromagnetic material | T_4441 | Materials that have been magnetized may become temporary or permanent magnets. If you bring a bar magnet close to pile of paper clips, the paper clips will become temporarily magnetized, as all their magnetic domains line up. As a result, the paper clips will stick to the magnet and also to each other (see the Figure 1.2). However, if you remove the paper clips from the bar magnets magnetic field, their magnetic domains will no longer align. As a result, the paper clips will no longer be magnetized or stick together. If you stroke an iron nail with a bar magnet, the nail will become a permanent (or at least long-lasting) magnet. You can see how its done in the Figure 1.3. The nails magnetic domains will remain aligned even after you remove the nail from the magnetic field of the bar magnet. Q: Even permanent magnets can be demagnetized if they are dropped or heated to high temperatures. Can you explain why? | text | null |
L_0899 | ferromagnetic material | T_4441 | Materials that have been magnetized may become temporary or permanent magnets. If you bring a bar magnet close to pile of paper clips, the paper clips will become temporarily magnetized, as all their magnetic domains line up. As a result, the paper clips will stick to the magnet and also to each other (see the Figure 1.2). However, if you remove the paper clips from the bar magnets magnetic field, their magnetic domains will no longer align. As a result, the paper clips will no longer be magnetized or stick together. If you stroke an iron nail with a bar magnet, the nail will become a permanent (or at least long-lasting) magnet. You can see how its done in the Figure 1.3. The nails magnetic domains will remain aligned even after you remove the nail from the magnetic field of the bar magnet. Q: Even permanent magnets can be demagnetized if they are dropped or heated to high temperatures. Can you explain why? | text | null |
L_0899 | ferromagnetic material | T_4442 | Some materials are natural permanent magnets. The most magnetic material in nature is the mineral magnetite, also called lodestone (see Figure 1.4). The magnetic domains of magnetite naturally align with Earths axis. The picture on the left shows a chunk of magnetite attracting small bits of iron. The magnetite spoon compass shown on the right dates back about 2000 years and comes from China. The handle of the spoon always points north. Clearly, the magnetic properties of magnetite have been recognized for thousands of years. | text | null |
L_0901 | force | T_4445 | Force is defined as a push or pull acting on an object. There are several fundamental forces in the universe, including the force of gravity, electromagnetic force, and weak and strong nuclear forces. When it comes to the motion of everyday objects, however, the forces of interest include mainly gravity, friction, and applied force. Applied force is force that a person or thing applies to an object. Q: What forces act on Carsons scooter? A: Gravity, friction, and applied forces all act on Carsons scooter. Gravity keeps pulling both Carson and the scooter toward the ground. Friction between the wheels of the scooter and the ground prevent the scooter from sliding but also slow it down. In addition, Carson applies forces to his scooter to control its speed and direction. | text | null |
L_0901 | force | T_4446 | Forces cause all motions. Everytime the motion of an object changes, its because a force has been applied to it. Force can cause a stationary object to start moving or a moving object to change its speed or direction or both. A change in the speed or direction of an object is called acceleration. Look at Carsons brother Colton in the Figure starts the scooter moving in the opposite direction. The harder he pushes against the ground, the faster the scooter will go. How much an object accelerates when a force is applied to it depends not only on the strength of the force but also on the objects mass. For example, a heavier scooter would be harder to accelerate. Colton would have to push with more force to start it moving and move it faster. Q: What units do you think are used to measure force? A: The SI unit for force is the Newton (N). A Newton is the force needed to cause a mass of 1 kilogram to accelerate at 1 m/s2 , so a Newton equals 1 kg m/s2 . The Newton was named for the scientist Sir Isaac Newton, who is famous for his laws of motion and gravity. | text | null |
L_0901 | force | T_4447 | Force is a vector, or a measure that has both size and direction. For example, Colton pushes on the ground in the opposite direction that the scooter moves, so thats the direction of the force he is applies. He can give the scooter a strong push or a weak push. Thats the size of the force. Like other vectors, a force can be represented with an arrow. You can see some examples in the Figure 1.2. The length of each arrow represents the strength of the force, and the way the arrow points represents the direction of the force. Q: How could you use arrows to represent the forces that start Coltons scooter moving? A: Colton pushes against the ground behind him (to the right in the Figure 1.1). The ground pushes back with equal force to the left, causing the scooter to move in that direction. Force arrows A and B in example 2 in the Figure 1.1) could represent these forces. | text | null |
L_0902 | forms of energy | T_4448 | Energy, or the ability to cause changes in matter, can exist in many different forms. Energy can also change from one form to another. The photo above of the guitar player represents six forms of energy: mechanical, chemical, electrical, light, thermal, and sound energy. Another form of energy is nuclear energy. Q: Can you find the six different forms of energy in the photo of the guitar player (See opening image)? A: The guitarist uses mechanical energy to pluck the strings of the guitar. He gets the energy he needs to perform from chemical energy in food he ate earlier in the day. The stage lights use electrical energy, which they change to light energy and thermal energy (commonly called heat). The guitar produces sound energy when the guitarist plucks the strings. | text | null |
L_0902 | forms of energy | T_4449 | The different forms of energy are defined and illustrated below. 1. Mechanical energy is the energy of movement. It is found in objects that are moving or have the potential to move. 2. Chemical energy is energy that is stored in the bonds between the atoms of compounds. If the bonds are broken, the energy is released and can be converted to other forms of energy. This portable guitar amplifier can run on batteries. Batteries store chemical energy and change it to electrical energy. 3. Electrical energy is the energy of moving electrons. Electrons flow through wires to create electric current. 4. Electromagnetic energy is energy that travels through space as electrical and magnetic waves. The light flooding the stage in the Figure 1.3 is one type of electromagnetic energy. Other types include radio waves, microwaves, X rays, and gamma rays. 5. Thermal energy is the energy of moving atoms of matter. All matter has thermal energy because atoms of all matter are constantly moving. An object with more mass has greater thermal energy than an object with less mass because it has more atoms. Why is this jogger sweating so much? His sweat is soaking up his shirt because he has so much thermal energy. Jogging is hot work because of the heat from the sun and the hard work he puts into his run. 6. Sound energy is a form of mechanical energy that starts with a vibration in matter. For example, the singers voice 7. Nuclear energy is energy that is stored in the nuclei of atoms because of the strong forces that hold the nucleus together. The energy can be released in nuclear power plants by splitting nuclei apart. It is also released when unstable (radioactive) nuclei break down, or decay. Q: The fans at a rock concert also produce or use several forms of energy. What are they? A: The fans see the concert because of electromagnetic energy (light) that enters their eyes from the well-lit musicians on stage. They hear the music because of the sound energy that reaches their ears from the amplifiers. They use mechanical energy when they clap their hands and jump from their seats in excitement. Their bodies generate thermal energy, using the chemical energy stored in food they have eaten. | text | null |
L_0902 | forms of energy | T_4449 | The different forms of energy are defined and illustrated below. 1. Mechanical energy is the energy of movement. It is found in objects that are moving or have the potential to move. 2. Chemical energy is energy that is stored in the bonds between the atoms of compounds. If the bonds are broken, the energy is released and can be converted to other forms of energy. This portable guitar amplifier can run on batteries. Batteries store chemical energy and change it to electrical energy. 3. Electrical energy is the energy of moving electrons. Electrons flow through wires to create electric current. 4. Electromagnetic energy is energy that travels through space as electrical and magnetic waves. The light flooding the stage in the Figure 1.3 is one type of electromagnetic energy. Other types include radio waves, microwaves, X rays, and gamma rays. 5. Thermal energy is the energy of moving atoms of matter. All matter has thermal energy because atoms of all matter are constantly moving. An object with more mass has greater thermal energy than an object with less mass because it has more atoms. Why is this jogger sweating so much? His sweat is soaking up his shirt because he has so much thermal energy. Jogging is hot work because of the heat from the sun and the hard work he puts into his run. 6. Sound energy is a form of mechanical energy that starts with a vibration in matter. For example, the singers voice 7. Nuclear energy is energy that is stored in the nuclei of atoms because of the strong forces that hold the nucleus together. The energy can be released in nuclear power plants by splitting nuclei apart. It is also released when unstable (radioactive) nuclei break down, or decay. Q: The fans at a rock concert also produce or use several forms of energy. What are they? A: The fans see the concert because of electromagnetic energy (light) that enters their eyes from the well-lit musicians on stage. They hear the music because of the sound energy that reaches their ears from the amplifiers. They use mechanical energy when they clap their hands and jump from their seats in excitement. Their bodies generate thermal energy, using the chemical energy stored in food they have eaten. | text | null |
L_0902 | forms of energy | T_4449 | The different forms of energy are defined and illustrated below. 1. Mechanical energy is the energy of movement. It is found in objects that are moving or have the potential to move. 2. Chemical energy is energy that is stored in the bonds between the atoms of compounds. If the bonds are broken, the energy is released and can be converted to other forms of energy. This portable guitar amplifier can run on batteries. Batteries store chemical energy and change it to electrical energy. 3. Electrical energy is the energy of moving electrons. Electrons flow through wires to create electric current. 4. Electromagnetic energy is energy that travels through space as electrical and magnetic waves. The light flooding the stage in the Figure 1.3 is one type of electromagnetic energy. Other types include radio waves, microwaves, X rays, and gamma rays. 5. Thermal energy is the energy of moving atoms of matter. All matter has thermal energy because atoms of all matter are constantly moving. An object with more mass has greater thermal energy than an object with less mass because it has more atoms. Why is this jogger sweating so much? His sweat is soaking up his shirt because he has so much thermal energy. Jogging is hot work because of the heat from the sun and the hard work he puts into his run. 6. Sound energy is a form of mechanical energy that starts with a vibration in matter. For example, the singers voice 7. Nuclear energy is energy that is stored in the nuclei of atoms because of the strong forces that hold the nucleus together. The energy can be released in nuclear power plants by splitting nuclei apart. It is also released when unstable (radioactive) nuclei break down, or decay. Q: The fans at a rock concert also produce or use several forms of energy. What are they? A: The fans see the concert because of electromagnetic energy (light) that enters their eyes from the well-lit musicians on stage. They hear the music because of the sound energy that reaches their ears from the amplifiers. They use mechanical energy when they clap their hands and jump from their seats in excitement. Their bodies generate thermal energy, using the chemical energy stored in food they have eaten. | text | null |
L_0902 | forms of energy | T_4449 | The different forms of energy are defined and illustrated below. 1. Mechanical energy is the energy of movement. It is found in objects that are moving or have the potential to move. 2. Chemical energy is energy that is stored in the bonds between the atoms of compounds. If the bonds are broken, the energy is released and can be converted to other forms of energy. This portable guitar amplifier can run on batteries. Batteries store chemical energy and change it to electrical energy. 3. Electrical energy is the energy of moving electrons. Electrons flow through wires to create electric current. 4. Electromagnetic energy is energy that travels through space as electrical and magnetic waves. The light flooding the stage in the Figure 1.3 is one type of electromagnetic energy. Other types include radio waves, microwaves, X rays, and gamma rays. 5. Thermal energy is the energy of moving atoms of matter. All matter has thermal energy because atoms of all matter are constantly moving. An object with more mass has greater thermal energy than an object with less mass because it has more atoms. Why is this jogger sweating so much? His sweat is soaking up his shirt because he has so much thermal energy. Jogging is hot work because of the heat from the sun and the hard work he puts into his run. 6. Sound energy is a form of mechanical energy that starts with a vibration in matter. For example, the singers voice 7. Nuclear energy is energy that is stored in the nuclei of atoms because of the strong forces that hold the nucleus together. The energy can be released in nuclear power plants by splitting nuclei apart. It is also released when unstable (radioactive) nuclei break down, or decay. Q: The fans at a rock concert also produce or use several forms of energy. What are they? A: The fans see the concert because of electromagnetic energy (light) that enters their eyes from the well-lit musicians on stage. They hear the music because of the sound energy that reaches their ears from the amplifiers. They use mechanical energy when they clap their hands and jump from their seats in excitement. Their bodies generate thermal energy, using the chemical energy stored in food they have eaten. | text | null |
L_0904 | frequency and pitch of sound | T_4452 | How high or low a sound seems to a listener is its pitch. Pitch, in turn, depends on the frequency of sound waves. Wave frequency is the number of waves that pass a fixed point in a given amount of time. High-pitched sounds, like the sounds of the piccolo in the Figure 1.1, have high-frequency waves. Low-pitched sounds, like the sounds of the tuba Figure 1.1, have low-frequency waves. | text | null |
L_0904 | frequency and pitch of sound | T_4453 | The frequency of sound waves is measured in hertz (Hz), or the number of waves that pass a fixed point in a second. Human beings can normally hear sounds with a frequency between about 20 Hz and 20,000 Hz. Sounds with frequencies below 20 hertz are called infrasound. Infrasound is too low-pitched for humans to hear. Sounds with frequencies above 20,000 hertz are called ultrasound. Ultrasound is too high-pitched for humans to hear. Some other animals can hear sounds in the ultrasound range. For example, dogs can hear sounds with frequencies as high as 50,000 Hz. You may have seen special whistles that dogsbut not peoplecan hear. The whistles produce sounds with frequencies too high for the human ear to detect. Other animals can hear even higher-frequency sounds. Bats, like the one pictured in the Figure 1.2, can hear sounds with frequencies higher than 100,000 Hz! Q: Bats use ultrasound to navigate in the dark. Can you explain how? A: Bats send out ultrasound waves, which reflect back from objects ahead of them. They sense the reflected sound waves and use the information to detect objects they cant see in the dark. This is how they avoid flying into walls and trees and also how they find flying insects to eat. | text | null |
L_0904 | frequency and pitch of sound | T_4453 | The frequency of sound waves is measured in hertz (Hz), or the number of waves that pass a fixed point in a second. Human beings can normally hear sounds with a frequency between about 20 Hz and 20,000 Hz. Sounds with frequencies below 20 hertz are called infrasound. Infrasound is too low-pitched for humans to hear. Sounds with frequencies above 20,000 hertz are called ultrasound. Ultrasound is too high-pitched for humans to hear. Some other animals can hear sounds in the ultrasound range. For example, dogs can hear sounds with frequencies as high as 50,000 Hz. You may have seen special whistles that dogsbut not peoplecan hear. The whistles produce sounds with frequencies too high for the human ear to detect. Other animals can hear even higher-frequency sounds. Bats, like the one pictured in the Figure 1.2, can hear sounds with frequencies higher than 100,000 Hz! Q: Bats use ultrasound to navigate in the dark. Can you explain how? A: Bats send out ultrasound waves, which reflect back from objects ahead of them. They sense the reflected sound waves and use the information to detect objects they cant see in the dark. This is how they avoid flying into walls and trees and also how they find flying insects to eat. | text | null |
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