Work and Energy

Energy is a measure of the cost to perform some action.

The SI unit of energy is the Joule:

                               m^2
             1 Joule = 1 kg * -----
                               s^2

One Joule is a very small amount of energy.

Work is the energy spent by a force acting through a distance:
```
             Work    =  (force) * (distance parallel to force)
```
or, in general
```
             Work    =  (force) * (displacement) * cos(theta)
```
where theta is the angle between the direction of the force and the displacement.
The unit of work is Newtons times meters, which turns out to be the same as Joules.
When a force acts in the same direction as displacement, it performs positive work (speeds things up).
When a force acts in the direction opposite to displacement, it performs negative work (slows things down).
Kinetic energy is another sort of energy, associated with moving objects:
```
               KE    = 0.5 * (mass) * (speed)^2
```

One can change the kinetic energy of an object by doing work on it:

          work done on object  =   change in kinetic energy

                               =   KE(final)      -    KE(initial)

                                             2                   2
                               =  0.5 * M * v     -   0.5 * M * v
                                             f                   i

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