How's that for confusing!
When you use energy, you do work. For this reason, both energy and work are measured in the same unit.... the Joule.
What does it take to do work?You
must move something.
This is somewhat counterintuitive because
you may think like this: If I push on a door and it doesn't move,
my muscles still get sore. I must have done some work.
In this case, no work was done on the
door; the work was done on your own body because your parts did all the
moving.
Your muscles used some of their energy
to try to move the door, but they only expanded and contracted with no
outward results.
Where do joules come from?
The easiest explanation is to use the idea of work...
Work is energy being used. To
use energy, something must be moved.
What moves things? Forces.
When things move, how do we measure
this? Meters.
Defined: one joule is used to move one
Kilogram one meter.
One Joule = Newton * Meter = Kg*m/s/s
* m = Kg*m2/s2
Instead of saying "kilogram meters squared per second
squared" somebody decided to use a famous
guy's name, so now we just say Joule.
1J = 1Kg*m²/s².