Just about any change matter undergoes requires energy to make it happen. Some examples:
Energy can make things hot: heating up something on a stove involves adding energy to it.
Energy can make things glow: electrical energy being dissipated in a light bulb will make it glow.
Energy can make things change shape: You can fold a piece of
paper, but it takes some mechanical energy to do it. Stuff that's made
out of metal needs to be bent into shape, and that means energy needs
to be added to bend the metal.
Energy can break stuff: Dropping a glass on a tile floor will
first exchange gravitational potential energy for kinetic energy, and
then finally into the energy required to break the bonds holding the
glass together as it shatters.
Energy can make music: Pluck a guitar string or blow a horn --
that takes energy. Sound waves carry energy through the air to the
Energy makes waves crash on the beach -- the water moves, carrying kinetic and gravitational potential energy.
Energy makes clocks run -- wind up a spring, or plug it in the wall, it takes energy to go.
Energy can change from one form to another:
electricity -> heat in the toaster
chemical potential energy to heat in a fire
chemical potential energy to kinetic energy in a car
gravitational potential energy to kinetic energy in a falling object
Einstein's E=mc^2 says we can even turn energy into matter!
(republished on 07/25/06)