Nerd Pride Radio

Re: Potential energy is just made up, right?

2019-03-19T14:49:21-06:00

Let me tell you. I understood physics much better 10 years after college. Not sure why I didn't understood it that well back then.

Statistics: Posted by FlameBlade — Tue Mar 19, 2019 3:49 pm

Re: Potential energy is just made up, right?

2019-03-19T14:32:03-06:00

I was being largely tongue in cheek above, because my son is studying this in high school science. But in all seriousness, the law of conservation of energy states that energy can neither be created nor destroyed, only converted into other forms. So when I throw the ball straight up, its kinetic energy eventually drop to zero, and at the very top, it is not moving at all for a split second, having converted all of that kinetic energy into potential energy.

And that potential energy has a functional reality that is calculable, because shortly, all the potential will be reconverted into kinetic energy for the fall (less losses to friction). It just bugs me, because when I first saw this in 7th grade, my teacher could not give a satisfactory answer to where that potential energy exists or how it is measured other than "we know we will get X amount of energy out of it, so X joules must necessarily be stored in there somewhere", like a big old D-cell battery.

Also on the test we just studied for: Why does science use models?

Science often uses models because the actual phenomena can be difficult to observe directly, and because simplified models can make complex concepts easier to understand.

Statistics: Posted by Mike — Tue Mar 19, 2019 3:32 pm

Re: Potential energy is just made up, right?

2019-03-19T13:54:49-06:00

Talk more later, but look at the units for kinetic energy, and compare to units for potential energy.

Also, it's about how you frame the reference. The formula for potential energy is mass*gravity*height, when relative to gravity, and what exactly is height?

The truth is much more complicated, and in a sense, Potential energy is a simplified way of computing given conditions given.

I mean, if one starts dropping at height h, with gravity g, do an integration over y axis to compute the speed of the ball when it hits the ground?

Or you have all computations done in form of KE vs PE at one shot?

In fact, PE is really mass*(sum of vectors for forces over n dimensions) * (distance between two points, where one point is at rest, and other point is where you are measuring velocity)

But that's ugly.

Statistics: Posted by FlameBlade — Tue Mar 19, 2019 2:54 pm

Re: Potential energy is just made up, right?

2019-03-19T13:27:05-06:00

I don't think the depth of the pool determines potential energy. I thought potential energy was essentially shorthand used to describe countervailing forces that are acting on an object, but zeroing out. So the person on the diving board has the force of gravity pulling them down, but the inertial forces of the board and structure holding them up. The depth of the pool doesn't affect that, does it?

Or do I grossly misunderstand what potential energy is?

Statistics: Posted by Kyle — Tue Mar 19, 2019 2:27 pm

Potential energy is just made up, right?

2019-03-19T08:36:42-06:00

Haven't you always suspected that "potential" energy is just a hoax perpetrated by physicists so that their equations will all balance?

I lift the ball into the air. It's not moving right now, but by raising it up, I've imbued it with potential energy so that it will move when I let it go. Okay, great... so where is that energy? How do I measure it? So if I climb up on the diving platform, I have X amount of potential energy stored in me to allow me to drop back to the pool. But what if they empty the pool and dig it deeper while I'm standing up there? Now I have MORE potential energy within me, even though I didn't move?

It's a hoax. I'm sure of it.

Statistics: Posted by Mike — Tue Mar 19, 2019 9:36 am