Energy

[Caity]

can energy be created or destroyed? i was talking to someone who told me that energy couldn't be created or destroyed, but i wasn't entierly sure, because i thought you could create energy, like friction (rubbing your hands together or making a fire). just wondering...

[gen2]

The full definition is:
Energy cannot be created or destroyed - it can only be changed from one form to another.
The main types are:
  Chemical
  Heat
  Light
  Sound
  Electricity
  Kinetic
  Potential
  (Atomic)

In the example you have given where friction is used to make fire, the conversion is from kinetic to heat.  Once the fire starts, the conversion is then chemical (the substance burning) to heat + light.

The last type (atomic) allows the conversion between mass and energy according to Einstein's famous equation  E=mc^2

[jake-the-peg]

When you rub your hands together, you convert chemical energy stored in your muscles to kinetic energy (motion). The friction that results from this converts that energy into thermal (heat) energy.

This is what's called the Conservation of Energy. There are a number of so called conservation laws in science - Energy is the simplest one - these are related to what we call symetries and have a very deep meaning in how the universe works

[Caity]

Thanks guys :)