| A | B |
|---|
| Energy | the ability to do work |
| kinetic energy | energy of motion |
| potential energy | energy of shape or position |
| mechanical energy | the total energy of motion and position of an object |
| energy conversion | a change from one form of energy into another |
| friction | a force that opposes motion between two surfaces that are touching |
| law of conservation of energy | the law that states that energy is neither created nor destroyed |
| energy resource | a natural resource that can be converted by humans into other forms of energy in order to do useful work |
| renewable resource | natural resources that can be used and replaced over a relatively short time |
| nonrenewable resource | natural resources that cannot be replaced or that can be replaced only over thousands or millions of years |
| fossil fuels | nonrenewable energy resources that form in the Earth's crust over millions of years from the buried remains of once-living organisms |
| biomass | organic matter, such as plants, wood, and waste, that can be burned to release energy |
| geothermal energy | thermal energy resulting from the heating of the Earth's crust |
| nuclear energy | generated from radioactive elements; splitting radioactive elements through nuclear fission |
| solar energy | energy from the sun |
| closed system | a well-defined group of objects that transfer energy between one another |
| perpetual motion machine | a machine that runs forever without any addition energy |
