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Time
Time is the never-ending continued progress of existence and events. It happens in an apparently irreversible way from the past, through the present to the future.
To measure time, we can use anything that repeats itself regularly. One example is the start of a new day (as Earth rotates on its axis). Two more are the phases of the moon (as it orbits the Earth), and the seasons of the year (as the Earth orbits the Sun).
Even in ancient times, people developed calendars to keep track of the number of days in a year. They also developed sundials that used the moving shadows cast by the sun through the day to measure times smaller than a day. Today, highly accurate clocks can measure time in less than a billionth of a second. The study of time measurement is known as horology.
The SI (International Systems of Units) unit of time is one second, written as s. When used as a variable in mathematics, time is often represented by the symbol formula_1.
In Einsteinian physics, time and space can be combined into a single concept. For more on the topic, see space-time continuum.
Force
In physics, a force is an interaction between "objects". It is called an interaction because if one object acts on another, its action is "matched" by a reaction from the other object. This idea is known as Newton's third law, where "action" and "reaction" are "equal and opposite" ("matched").
The "objects" are just the things the force acts between. Different forces act between different sorts of object. For example, gravity acts between objects with mass, like the sun and the earth. Another example is electromagnetic force, which acts between objects with charge, like an electron and the nucleus of an atom. "Gravity" and "electromagnetic force" are two examples of forces.
A force changes the state of an object (some physical quantity changes) or, strictly, the states of two objects, since the force is an interaction. For example, a force causes an affected object to be pushed or pulled in a certain direction. This changes the object's momentum. Forces cause objects to accelerate, add to the object's overall pressure, change direction, or change shape. The strength of a force is measured in Newtons (N). There are four fundamental forces in physics.
A force is always a push, pull, or a twist, and it affects objects by pushing them up, pulling them down, pushing them to a side, or by changing their motion or shape in some other way.
According to Newton's Second Law of Motion, the formula for finding force is:
where formula_2 is the force,
formula_3 is the mass of an object,
and formula_4 is the acceleration of the object.
This formula says that when there is a force on an object then it will move faster and faster.
If the force is weak and the object is heavy, then it will take a long time to increase the speed very much,
but if the force is strong and the object is light, then it will move a lot faster very quickly.
Gravity is an acceleration. Everything that has a mass is being pulled toward the Earth because of that acceleration. This pull is a force called weight.
One can take the equation above and change formula_4 to the standard gravity "g", then a formula about the gravity on earth can be found:
where formula_7 is the weight of an object,
formula_3 is the mass of an object,
and formula_9 is the acceleration due to gravity at sea level. It is about formula_10.
This formula says that when you know the mass of an object, then you can calculate how much force there is on the object because of gravity.
You must be on earth to use this formula. If you are on the moon or another planet, then you can use the formula but "g" will be different.
Force is a vector, so it can be stronger or weaker and it can also point in different directions.
Gravity always points down into the ground (if you are not in space).
Another equation that says something about gravity is:
formula_2 is force; formula_13 is the gravitational constant, which is used to show how gravity accelerates an object; formula_14 is the mass of one object; formula_15 is the mass of the second object; and formula_16 is the distance between the objects.
This equation is used to calculate how the earth moves around the sun and how the moon moves around the earth. It is also used to calculate how other planets, stars and objects in space move around.
The equation says that if two objects are very heavy then there is a strong force between them because of gravity.
If they are very far apart then the force is weaker.
Laboratory techniques
Laboratory techniques are the techniques of handling the various pieces of apparatus.
Ways to dissolve a solid in a liquid or to mix two liquids in a test tube:
International System of Units
The International System of Units is the standard modern form of the metric system. The name of this system can be shortened or abbreviated to SI, from the French name "Système International d'unités".
The International System of Units is a system of measurement based on 7 base units: the metre (length), kilogram (mass), second (time), ampere (electric current), Kelvin (temperature), mole (quantity), and candela (brightness). These base units can be used in combination with each other. This creates "SI derived units", which can be used to describe other quantities, such as volume, energy, pressure, and velocity.
The system is used almost globally. Only Myanmar, Liberia, and the United States do not use SI as their official system of measurement. In these countries, though, SI is commonly used in science and medicine.
The metric system was created in France after the French Revolution in 1789. The original system only had two standard units, the kilogram and the metre. The metric system became popular amongst scientists.
In the 1860s, James Clerk Maxwell and William Thomson (later known as Lord Kelvin) suggested a system with three base units - length, mass, and time. Other units would be derived from those three base units. Later, this suggestion would be used to create the centimetre-gram-second system of units (CGS), which used the centimetre as the base unit for length, the gram as the base unit for mass, and the second as the base unit for time. It also added the dyne as the base unit for force and the erg as the base unit for energy.
As scientists studied electricity and magnetism, they realized other base units were needed to describe these subjects. By the middle of the 20th century, many different versions of the metric system were being used. This was very confusing.
In 1954, the 9th General Conference on Weights and Measures (CGPM) created the first version of the International System of Units. The six base units that they used were the metre, kilogram, second, ampere, Kelvin, and candela. The seventh base unit, the mole, was added in 1971.
SI is now used almost everywhere in the world, except in the United States, Liberia and Myanmar, where the older imperial units are still widely used. Other countries, most of them historically related to the British Empire, are slowly replacing the old imperial system with the metric system or using both systems at the same time.
The SI base units are measurements used by scientists and other people around the world. All the other units can be written by combining these seven base units in different ways. These other units are called "derived units".
Derived units are created by combining the base units. The base units can be divided, multiplied, or raised to powers. Some derived units have special names. Usually these were created to make calculations simpler.
Very large or very small measurements can be written using prefixes. Prefixes are added to the beginning of the unit to make a new unit. For example, the prefix "kilo-" means "1000" times the original unit and the prefix "milli-" means "0.001" times the original unit. So one "kilometre" is 1000 metres and one "milligram" is a 1000th of a gram.
Lake Michigan
Lake Michigan is one of the five Great Lakes in North America. It has a surface area of . It is wide. Lake Michigan is the 5th largest lake in the world.
Lake Michigan is surrounded by the U.S. states of Indiana, Illinois, Wisconsin, and Michigan. It is the only Great Lake that is not partly in Canada. The largest city on the shore of Lake Michigan is Chicago.
The earliest time that people lived near the lake was 800 CE. The word "Michigan" originally meant the lake itself. It is believed to come from the Ojibwa word "mishigami" meaning "great water".
The first person to reach the deepest part of Lake Michigan was J. Val Klump. Klump reached the bottom with a submarine as part of a 1985 research expedition.
Twelve million people live along Lake Michigan's shores. They are mainly in the Chicago and Milwaukee areas.
Gas syringe
A gas syringe is a tool used in a laboratory. It is used to collect a gas or to measure the volume of a gas.
Simple systems can be settled in the laboratory to collect gas or to compress it. It is usually used to explain Gas Law.
Mixture
In chemistry, a mixture is a substance that is made up of two or more simpler substances. These substances can be chemical elements or compounds. A mixture can be made of liquids, solids, or gases.
A mixture is not the same as a compound which is made of two or more atoms connected together. For instance, a mixture of the gases hydrogen and nitrogen contains hydrogen and nitrogen, not the compound ammonia which is made of hydrogen and nitrogen atoms.
A mixture where the different parts can be distinguished easily is called "heterogenous", one where this is not the case is called "homogeneous". A third form is called colloid.
If one substance in a mixture dissolves in the other, it is called a solution. For example, if sugar is put in water it forms a mixture, then dissolves to make a solution. If it does not dissolve, it would be called a suspension.
Solids can be mixtures also. Alloys are mixtures. Many kinds of soil and rock are mixtures of different minerals. Thus, a mixture is made of two or more elements and/or compounds which are not chemically combined.
Language family
Language families are groups of languages that are related to each other because they come from a common older language. The languages in such a family are similar in their vocabulary or structure.
For example, French and Spanish both come from Latin. Latin was spoken a long time ago, and some of the people who spoke it started to speak one way, saying, for example, for good: "bueno" while another group started saying "bon." Most words are said a little differently in Spanish and French, so the two are called different languages.
Most languages belong to a language family, but some languages do not. These languages are called Language isolates.
There also are constructed languages, like for example Esperanto. Constructed languages are made for different reasons: making a 'world language', for fun, for use in fiction, etc.
"Ethnologue" 22 (2019) lists these language families as "major". Each has at least 1% of all languages on Earth:
"Glottolog" 4.0 (2019) lists the following as the largest families, of 8494 languages:
Chess
Chess is a board game for two players. It is played in a square board, made of 64 smaller squares, with eight squares on each side. Each player starts with sixteen pieces: eight pawns, two knights, two bishops, two rooks, one queen and one king. The goal of the game is for each player to try and checkmate the king of the opponent. Checkmate is a threat ('check') to the opposing king which no move can stop. It ends the game.
During the game the two opponents take turns to move one of their pieces to a different square of the board. One player ('White') has pieces of a light color; the other player ('Black') has pieces of a dark color. There are rules about how pieces move, and about taking the opponent's pieces off the board. The player with white pieces always makes the first move. Because of this, White has a small advantage, and wins more often than Black in tournament games.
Chess is popular and is often played in competitions called chess tournaments. It is enjoyed in many countries, and is a national hobby in Russia.
Most historians agree that the game of chess was first played in northern India during the Gupta Empire in the 6th century . This early type of chess was known as "Chaturanga", a Sanskrit word for the military. The Gupta chess pieces were divided like their military into the infantry, cavalry, elephants, and chariots. In time, these pieces became the pawn, knight, bishop, and rook. The English words "chess" and "check" both come from the Persian word "shāh" meaning king.
The earliest written evidence of chess is found in three romances (epic stories) written in Sassanid Persia around 600. The game was known as "chatrang" or "shatranj". When Persia was taken over by Muslims (633–644) the game was spread to all parts of the Muslim world. Muslim traders carried the game to Russia and to Western Europe. By the year 1000 it had spread all over Europe. In the 13th century a Spanish manuscript called "Libro de los Juegos" describes the games of "shatranj" (chess), backgammon, and dice.
The game changed greatly between about 1470 to 1495. The rules of the older game were changed in the West so that some of the pieces (queen, bishop) had more scope, development of the pieces was faster, and the game more exciting. The new game formed the basis of modern international chess. Historians of chess consider this as the most important change since the game was invented.
The rules of chess are governed by the World Chess Federation, which is known by the initials FIDE, meaning "Fédération Internationale des Échecs". The rules are in the section "Laws of Chess" of the "FIDE Handbook". FIDE also give rules and guidelines for chess tournaments.
Chess is played on a square board divided into eight rows of squares called ranks and eight columns called files, with a dark square in each player's lower left corner. This is altogether 64 squares. The colors of the squares are laid out in a checker (chequer) pattern in light and dark squares. To make speaking and writing about chess easy, each square has a name. Each rank has a number from 1 to 8, and each file a letter from "a" to "h". This means that every square on the board has its own label, such as g1 or f5. The pieces are in white and black sets. The players are called White and Black, and at the start of a game each player has 16 pieces. The 16 pieces are one king, one queen, two rooks, two bishops, two knights and eight pawns.
Definitions: vertical lines are "files"; horizontal lines are "ranks"; lines at 45° are "diagonals".
Each piece has its own way of moving around the board. The "X" marks the squares where the piece can move.
Most pieces capture as they move. If a piece lands on an opponent's piece, the opposing piece is taken off the board. There are three special cases:
If a move is made which attacks the opposing king, that king is said to be 'in check'. The player whose king is checked must make a move to remove the check. The options are: moving the king, capturing the threatening piece, or moving another piece between the threatening piece and the king. If the player whose king is in danger cannot do any of these things, it is checkmate, and the player loses the game.
Once in every game, each king can make a special move, known as "castling". When the king castles, it moves two squares to the left or right. When this happens, the rook is moved to stand on the opposite side of the King. Castling is only allowed if all of these rules are kept:
"En passant" ('in passing' in French) is a special capture. It is only available when a pawn moves forward two squares past an opposing pawn on an adjacent file. The opposing pawn must be on the 5th rank from its own side. Then the opponent's pawn can capture the double-mover "as if it had only moved one square forward". This option is open on the next move only.
For example, if the black pawn has just moved up two squares from g7 to g5, then the white pawn on f5 can take it by "en passant" on g6. The "en passant" rule was developed when pawns were allowed to make their double move. The rule made it more difficult for players to avoid pawn exchanges and blockade the position. It kept the game more open.
When a pawn moves to its eighth rank, it must be changed for a piece: a queen, rook, bishop, or knight of the same color (player's choice). Normally, the pawn is "queened", but in some advantageous cases another piece is chosen, called 'under-promotion'.
Checkmates are rare in competitive chess. The most common ends are decisions made by one or both players.
The FIDE rules for competitive chess include all the above rules, plus several others.
If players wish to adjust a piece on the board, they must first say "J'adoube" (I adjust) or the equivalent. Apart from that, if a piece is touched it must be moved if possible. This is the 'touch and move' law. If no legal move is possible with the touched piece, the player must make a legal move with another piece. When a player's hand leaves a piece after moving it then the move is over and may not be changed (if the move was legal).
There are a few famous cases where players appeared to break this rule without being punished. The most famous example was by the then World Champion Garry Kasparov against Judit Polgar in a top-class tournament.
Competitive games of chess must be played with special chess clocks which time a player only when it is his/her turn to move. The essence is that a player has to make a certain number of moves in a certain total time. After moving, the player presses a button on the clock. This stops the player's clock, and start's the opponent's clock. Usually the clocks are mechanical, but some are electronic. Electronic clocks can be set to various programs, and they can count moves made.
The moves of a chess game are written down by using a special chess notation. This is compulsory for any competitive game. Usually algebraic chess notation is used. In algebraic notation, each square has one and only one name (whether you are looking from White's side of the board or Black's). Here, moves are written in the format of: initial of piece moved – file where it moved – rank where it moved. For example, Qg5 means "queen moves to the g-file and 5th rank" (that is, to the square g5). If there are two pieces of the same type that can move to the same square, one more letter or number is added to show the file or rank from which the piece moved, e.g. Ngf3 means "knight from the g-file moves to the square f3". The letter P showing a pawn is not used, so that e4 means "pawn moves to the square e4".
If the piece makes a capture, "x" is written before the square in which the capturing piece lands on. Example: "Bxf3" means "bishop captures on f3". When a pawn makes a capture, the file from which the pawn left is used in place of a piece initial. For example: exd5 means "pawn captures on d5."
If a pawn moves to its eighth rank, getting a promotion, the piece chosen is written after the move, for example e1Q or e1=Q. Castling is written by the special notations 0-0 for kingside castling and 0-0-0 for queenside. A move which places the opponent's king in check normally has the notation "+" added. Checkmate can be written as # or ++. At the end of the game, 1-0 means "White won", 0-1 means "Black won" and ½-½ is a draw.
In print, "figurines" (like those in diagrams, but smaller) are used for the pieces rather than initials. This has the advantage of being language-free, whereas the initials of pieces are different in every language. Typefaces which include figurines can be purchased by chess authors. Also, basic notes can be added by using a system of well-known punctuation marks and other symbols. For example: ! means a good move, !! means a very good move, ? means a bad move, ?? a very bad move (sometimes called a "blunder"), !? a creative move that may be good, and ?! a doubtful move. The purpose of these methods is to make publications readable in a wider range of countries. For example, one kind of a simple "trap" known as the Scholar's mate, as in the diagram to the right, may be recorded:
1. e4 e5
2. Qh5?! Nc6
3. Bc4 Nf6?? (3...Qe7 would prevent the mate, with 4...Nf6 next move)
4. Qxf7# 1-0
With figurines in place of the initials, this would be understood by players everywhere.