For an object or force to do work, it needs energy. But, from where does the gravitational force get the energy to do work upon, say, a falling object? The gravitational force is doing work upon the object, isn't it?
I searched the internet and Physics SE, and found this. Caesar asked a similar question and udiboy1209 answered it.
Let's take the example of a ball dropped from some height. Gravity of the earth pulls it downward, doing work on the ball and giving it kinetic energy. The question you ask is where did it get this energy from? Go back a step and think about how this ball ended up at such a height? You lifted it up with your arms and put it on that height. Your arms did work against gravity, spent some energy to put that ball on that height. Where did that spent energy go? This was given to gravity!
When you do work against gravity, you store energy in the gravitational field as gravitational potential energy, which then gravity uses to do work on that object.
But isn't the work done by our arms stored on the ball? He says that the energy spent is stored in the gravitational field. Work is done upon the ball; shouldn't the energy be stored on the ball? If so, then where does gravitational force get its energy to do work upon the ball on the first place?