Although the above statement might seem surprising, even shocking, given the length we have gone to explain the importance of energy to the world and the possibility of a crisis in the future, it is absolutely true when speaking from a physics point of view.

One of the most important and firmly established laws of physics is that energy is conserved, that is, energy will always remain at the same level in a closed system. The Earth can be considered a closed system, and many people argue that the Earth gains a useful net energy from the sun. So strictly speaking, even though the following terms are widely used, we will never actually "run out" or "use up" energy.

The problem we actually have is related to the storage of energy. A store of energy is called a fuel. A high level of energy is stored in coal, natural gas, and oil, making them the three most widely used and important energy sources in the world. Unfortunately, when these fuels are burned in chemical or nuclear reactions to release the energy, the original fuel mass is used up and cannot be recreated without spending more energy than the amount that could be obtained (defeating the purpose of an energy source altogether!). It is for this reason that we must find viable, infinite sources of energy before our finite supplies run out.

Laws of physics dictate that energy can be change from one form to another (or into matter - the reason why there's energy in fossil fuels). There are various forms of energy: kinetic energy (energy of motion), potential energy, mechanical energy, nuclear energy, etc., but we cannot directly use these forms of energy to turn on our TV or to cook food in the microwave. That's where electricity comes in. Since electricity is the primary form of energy consumed by the majority of the world's population, power plants must exist to convert heat from burning biomass or kinetic energy from falling water into the energy that flows through the wire in our homes.

So, as you can see, physics is indeed important in understanding our energy use. Here are more sections that deal with the physics of energy: