Not all jobs need fuel

Not all jobs require a fuel to get them done

An important point to bear in mind here is that not all jobs require a fuel to get them done.

Lifting a book onto a shelf or a rocket into orbit do involve burning a fuel. The fuels are of different kinds, but both involve using up a supply of reacting chemicals. However, keeping the book on the shelf or the rocket in orbit do not require a supply of fuel. Changes are still happening, with the rocket zipping around the Earth and the book spinning around the Earth's axis along with everything else in the room. Both are moving even faster through our solar system, but none of these changes are powered; no fuel is used up.

In a similar way, dragging a sledge through snow or pushing a car along a road both burn up fuel, whereas the endless motion of gas molecules in the atmosphere or the planets' orbital motions around the sun involve no such continuous consumption. Burning a fuel gets some jobs done, but lots of changes happen without burning a fuel.

Here are some changes: some need a fuel and some do not.