# energy notes ### ENERGY

Notes and Key Concepts

## Work

An object’s motion is related to both force and how the force acts.

The quantity force X time = impulse

The quantity force X distance = work

## WORK

1.

2.

Two factors are considered when work is done

The application of a force

The movement of something by that force

The work done on an object by an applied force is the product of the force and the distance through which the object moved

Work=force x distance

W=Fd

## POWER

Power is the rate at which work is done

Power=work done/time interval

The unit of power is the joule per second, also known as the watt

One watt (W) of power is expended when one joule of work is done in one second

1 Kilowatt (kW)= 100 watts

1 megawatt (MW) = one million watts

### Metric System vs. United States

In the metric system, automobiles are rated in kilowatts

In the U.S, we rate engines in units of horsepower and electricity in kilowatts

One horsepower (hp, is the same as 0.75 kW, so an engine rated at 134 hp is a 100kW engine

### Mechanical Energy

Potential

Potential energy is stored and held in readiness (a spring or stretched rubber band)

Examples: fossil fuels, electric batteries, and food

Gravitational potential energy= weight x height

PE=mgh

Kinetic

Kinetic energy is energy of motion

It depends on mass and speed of an object

Kinetic energy = ½ mass x speed2