Field and Potential

Field and Potential

Lets look more closely at gravitational potential energy. You can lift up a stone anywhere on earth, to any height, and it would still have weight. In an abstract way, we can say that a force can act in the space around earth. Michael Faraday called this kind of space a field.

So a gravitational field is the space in which a gravitational force can act.

A stone that is higher up has more potential energy than a stone lower down. We know this because when the first stone falls, it hits the ground harder.

So some parts of a field has higher potential than other parts. An object in the field always tends to move from higher to lower potential.

Where does this potential energy come from?

In the case of the stone higher up, think about how it got up there - you lifted it up! In lifting it, you have done work against gravity. It is this work that produces the potential energy.

Exercise. I lift a ball up 1 m from the ground. My friend, who is 10 m away, lifts an identical ball to the same height. What is the difference in potential energy? Answer. There is no difference, because, to move the ball horizontally, no work needs to be done against gravity. If I keep my ball at the same height and walk over to my friend, my ball should now have the same potential as his. However, I would have done no additional work on the ball, even if I have done a lot on my leg muscles. So no potential energy is added to the ball, in moving from my original position. The potential energy must be the same as before I walked.

The Physics Notes