## Physics I: Chapter 7

Reference: Beginning Physics I

CHAPTER 7: ENERGY, POWER AND SIMPLE MACHINES

.

## KEY WORD LIST

Thermal Energy, Friction and Thermal Energy, Law of Conservation of Energy, Power, Simple Machine, Mechanical Advantage, Efficiency

.

## GLOSSARY

For details on the following concepts, please consult CHAPTER 7.

THERMAL ENERGY
When the motion of particles is of random nature (describable, in fact, only by statistical means) we call the associated energy thermal energy. Such energy manifests itself macroscopically in various ways, most notably as a rise in temperature.

FRICTION AND THERMAL ENERGY
Since friction always does negative work, the system that supplies the force of friction should always gain energy. The source of friction is the interaction between the surface layers of the two objects that are moving past each other. As a result, the random jiggling of the vast number of particles in the surface increases. This is the increase in the thermal energy of the surfaces.

LAW OF CONSERVATION OF ENERGY
If we include in our considerations thermal energy, as well as other forms of energy such as electromagnetic radiation (light) and more subtle form of mechanical energy such as sound, the law of conservation of energy still holds. Energy can be transformed from one type to another within a given system, and it can be transferred from one system to another system, but the total amount of energy remains the same.

POWER
Power is the rate at which work is done; that is, how much work is done per second by a force. The SI unit for power is the watt (W), where 1 W = 1 joule/second.

The instantaneous power is,

SIMPLE MACHINE
A simple machine is any device that allows a small force to move an object against a larger resisting force, or a force in one direction to move an object against a resisting force in another direction. Many simple machines do both. Examples of simple machines are lever, inclined plane and a pulley system.