Gravitational Potential Energy (4/7)
When you are calculating potential energy using U=mgh, the obvious question is "what is h?" or "height above what?"
The answer is pretty simple- anything you want, but be consistent. Understanding this point for the simple equation is essential for understanding it for the more complicated one we're trying to learn.
This is a bellwork I gave a class a few years back. I had them do some potential energy calculations in different reference frames.
In this problem, students calculated the potential energy (U) as well as the change in potential energy (ΔU) as a basketball fell in my second floor classroom, taking the floor as h=0. They then repeated the calculation using a reference frame that put the classroom below me's floor as h=0. Although U changed, ΔU did not. Since conservation of energy equations inherently depend on ΔU (see the bottom for this) this means that as long as we are consistent with our choice for h=0, we can pick any zero point we want.
When we talk about space, we're going to make the zero point a location that's easy to find for any object.
Gravitational Potential Energy (4/7)
When you are calculating potential energy using U=mgh, the obvious question is "what is h?" or "height above what?"
The answer is pretty simple- anything you want, but be consistent. Understanding this point for the simple equation is essential for understanding it for the more complicated one we're trying to learn.
This is a bellwork I gave a class a few years back. I had them do some potential energy calculations in different reference frames.
In this problem, students calculated the potential energy (U) as well as the change in potential energy (ΔU) as a basketball fell in my second floor classroom, taking the floor as h=0. They then repeated the calculation using a reference frame that put the classroom below me's floor as h=0. Although U changed, ΔU did not. Since conservation of energy equations inherently depend on ΔU (see the bottom for this) this means that as long as we are consistent with our choice for h=0, we can pick any zero point we want.
When we talk about space, we're going to make the zero point a location that's easy to find for any object.