3. Conversion of energy (Energy and work)

Can we consume or generate energy?
Strictly speaking: no. According to the conservation of energy rule, one of the basic laws of physics, energy cannot be lost or generated. It can only be transformed from one form of energy to another: for example an engine converts chemical energy in oil and gasoline into kinetic energy; a generator converts kinetic energy into electrical energy; an oven converts chemical energy into thermal energy (heat).

But, don’t we use energy when we cycle or drive? ...
What we consume is usable energy. That is, when we consume energy whilst cycling, we convert usable biochemical energy (sugar) into kinetic energy (muscles work to accelerate the bicycle and to keep moving despite frictional resistance). This kinetic energy is used to get to our destination. Ultimately, the chemical energy is converted into heat, which is no longer usable. That's why we always need new usable energy.
When refuelling at the gas station we give the car a lot of usable energy. When we have emptied the tank, this energy is no longer in the car’s system car, but in the form of heat in the environment. Ultimately, both body and the car engine transform chemical energy into heat, which is no longer usable energy. Systems such as animals or people, cars, and buildings that exchange energy with the environment in form of heat are called open systems. They always need new usable energy. Therefore, it makes perfect sense to optimize energy use, i.e. the consumption of usable energy.

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