Conservation law

A conservation law, also called a law of conservation, applies to physics. According to conservation laws, a measurable property does not change as long as it is within an isolated system. Common conservation laws include those about energy, mass, linear momentum, angular momentum, and charge.

Law of Conservation of Energy

The Law of Conservation of Energy states that energy does not change as long as it remains isolated. Suppose a car is locked in a garage. As long as it remains isolated—as long as it is in the garage—the amount of energy within it remains the same.

The second part of this law states that energy cannot be created or destroyed; it can only be changed from one form to another or transferred from one object to another. When you use energy, it is not gone; it is converted to another form. For example, if you turn on an air-conditioner, electrical energy is converted to cool energy. If you measure the amount of electricity used by the air-conditioner and the amount of cool air produced by the air-conditioner, the amounts will be the same.

Energy can also be transferred from one object to another. Imagine that a girl kicks a soccer ball and it hits a second ball that was on the field and not in motion. Now the energy from the first ball is transferred to the second ball and the second ball moves.

This formula is used to illustrate the Law of Conservation of Energy:

initial energy = final energy

It can be broken down like this:

(kinetic energy at time A + potential energy at time A) = (kinetic energy at time A + potential energy at time B)

Kinetic energyis moving energy. It is the energy an object possesses because it is in motion. Potential energy is an object's stored energy. It is the energy an object would have if it were in motion.

Law of Conservation of Mass

The Law of Conservation of Mass states that matter cannot be created or destroyed in chemical reactions. An amateur French chemist named Antoine-Laurent Lavoisier discovered the law around 1785. Lavoisier conducted many experiments with metals. He discovered that the mass gained by a metal during a chemical reaction was equal to the mass lost by the surrounding air. This concept is true of all matter in the universe—it can undergo a change, but the total mass remains the same. Because of his discovery, Lavoisier is considered the father of modern chemistry. (Lavoisier was later executed on suspicion of corrupting the tax-collection system even though he was innocent.)

Law of Conservation of Linear Momentum

According to the Law of Conservation of Linear Momentum, momentum cannot be lost; it has to go somewhere. Momentum refers to how strong a moving object is. Linear momentum (also known as linear motion) refers to the momentum of an object moving in a straight line or nearly a straight line. An object that is not moving has a momentum of zero.

Suppose you catch a baseball that your friend has thrown. The baseball is moving fast, so its momentum is strong. When you catch the ball, you lean in the direction that the ball was traveling because some of the ball's momentum is transferred to you. The larger and faster an object travels, the greater its momentum and the harder it is to stop. This is why a train traveling on tracks takes a while to stop—its momentum is great.

Law of Conservation of Angular Momentum

The Law of Conservation of Angular Momentum is similar to the previous law except that the object is spinning around a central point or an axis. Once again, momentum is not lost but transferred to another place. Stars and planets have angular momentum because they orbit the sun. Figure skaters spinning also have angular momentum. According to the Law of Conservation of Angular Momentum, an object will continue to spin unless an external force acts upon it—and if it does, the external force will gain momentum. The larger and faster the object is, the more difficult it is for an external force to stop it.

Law of Conservation of Charge

A charge refers to whether an object has more electrons or protons. An electron has a negative charge while a proton has a positive charge. If an object has more electrons than protons, then it is negatively charged. Likewise, if an object has more protons than electrons, then it is positively charged. The Law of Conservation of Charge states that an electric charge cannot be created or destroyed; it can only be transferred from one object to another. For example, if you rub a balloon against your hair, the balloon will pick up electrons and become negatively charged. Your hair has lost electrons, so it becomes positively charged. The total charge, however, is the same as it was before you rubbed the balloon against your hair.

Bibliography

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