What is Energy?
Well, that's a tricky one, because you can hardly walk into a
shop and ask `I'd like some energy please!' Energy
is an idea used to decribe a property of the system
being looked at.
Okay, okay, easy one....Joules.
Let's look at a car as a system and its
properties. One property of the system that is a car is its
length. Length expresses how long the car is.
If a car of mass `m' is moving at speed
`v' then it has a kinetic energy K given by the formula
K=mv2/2
The kinetic energy expresses how much `effort' had to be expended to
move a car of mass `m' moving at speed `v'. The car has
the property of kinetic energy.
Now suppose
the car crashes into a wall!
What happens? Well, there is a big crashing sound for sure
and maybe some of the bricks in the wall will get knocked out of the
wall. How did it happen? Well, the energy of the car's motion - its
kinetic energy - got converted into a crashing sound and lots of
moving bricks. So somehow the original `effort' of getting the car
moving got `transferred' into a motion of bricks and a crashing
sound. It takes `effort' to do all of that, and the idea of ENERGY
expresses the idea of that `effort'.
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