People make up names for different types of energy, but real energy doesn’t always fit into exactly one type or another. before we get into some of the different names, you should know one really important thing: energy can go from one form to another, but the total amount doesn’t change.
Here’s what the types you mentioned mean, and a few other types too.
Kinetic energy: Moving objects have energy. Often this is the easiest type of energy to see.
Gravitational energy: Any object sitting up away from the ground has gravitational energy. Every good Rube Goldberg device has to have some part where a ball drops, releasing some gravitational energy. Gravitational energy is called a type of "potential energy", because when it is lost you can get the easily seen "kinetic energy".
Electrical energy: It takes energy to pull apart positive and negative electrical charges. If they are pulled apart, we say that they have electrical energy. This is also a type of potential energy. When the positive and negative charges come back together, they speed up, so we say kinetic energy is gained and potential energy is lost.
Chemical Energy: The different ways that the atoms in a material stick together into molecules have different amounts of energy. When the types of molecules change to ones with lower energy, say when you burn some paper, the extra energy will come out. If you were to look inside the molecules, you could break up the chemical energy into an electrical part, which comes from how far apart the electrically charged particles are, and a kinetic part, from how fast they’re moving.
Solar energy: That just means any energy that comes from the sun. That just comes in as light or types of light that you can’t actually see, such as infrared light and ultraviolet light. Some people call the energy in light "radiant energy", but since light is just a wave of electricity and magnetism, you could call it electrical energy.
Sound energy: That’s energy of sound waves. It’s partly the kinetic energy of moving atoms and molecules. In solids and liquids it’s also potential energy from stretching and squashing the bonds between molecules.
There’s no real rhyme or reason to this sort of list, so maybe it’s best to stop here.
There’s also another important way to divide up energy types.
"Mechanical energy" is energy of big things you can see, like either a weight lifted off the ground or a weight falling down.
"Thermal energy", which depends on how hot things are, is energy of all the little inside parts jiggling around every which way. Even though the total amount of energy doesn’t change, energy keeps trickling away from the other forms into thermal energy. When people say "we should conserve energy" they mean we should try to hang on to useful forms instead of just turning them into thermal energy, say by burning fuels.
Tamara & Mike
(republished on 07/25/06)