If a ball is sitting in a highly concave bowl that is as close to the ground as it can possibly be, and there is no external force able to act on it, and it is not able to move in any direction whatsoever, does it still have potential energy?
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-1. Lack of effort and unclear. Please explain your difficulty. Why do you think it does or does not have PE in this situation? – sammy gerbil Feb 22 '17 at 00:50
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Potential energy is not absolute; in other words, you can't say what a object's energy is, only how it would change if it moved. So in your example all we can say is that if it was higher its energy would be higher, but it's meaningless to ask what its energy is. You could say that it's zero or you could say that it's a million joules, it's just a reference point.
Javier
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It's similar to ground on an electrical circuit. You often measure the potential relative to it because it is a base value that is easy to reference. That is the same reason we pick the ground as a base for potential gravitational energy. The truth is, you even have gravitational potential energy, relative to the gravitational potential at the centre of the earth. The ground is just a more reasonable value to choose as "0 gravitational potential" in situations where you likely wont have to deal with negative values below the ground. – JMac Feb 21 '17 at 21:51
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Yes, unless it is at absolute zero temperature, which is impossible. The atoms comprising the ball have plenty of potential energy,
As opposed to the mechanical P.E. you are trying to eliminate in your question, the bonds between the atoms in the molecular structure do have chemical potential energy.
Depending on the temperature of the ball, (usually proportional to it) there are stresses within the ball that in effect store energy,
In classical terms, the ball may seem still, but even on this level, the ball will move about slightly, due to internal stresses, although how much detection effort you want to put into this is another question.
Image source: Molecular Composition of Rubber
This a picture of the molecules within rubber, to take one example of the material a ball might be made of. Each molecular group can be imagined as being joined together by spring-like forces, and where you have springs, you have potential energy.
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1It clearly has chemical potential, but i meant potential on a macroscopic level. I was also referring to mechanical potential energy, not chemical. – TECTEC3 Studios Feb 23 '17 at 23:14
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1I do see where you're coming from, I should've made that more clear in my question. – TECTEC3 Studios Feb 23 '17 at 23:16
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Ok, my point was to do an answer for other people to realise that chemical potential is involved, as this is a resource site. And yeah, I have had to tweak my own questions more than I like to admit. As a compromise, we might agree that the chemical potential can lead to tiny, tiny mechanical stresses. – Feb 23 '17 at 23:20
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Yes, it has PE but a very small amount. Let's assume that the bowl is on a table. The difference in height between the ball being in the bowl on the table and on the table itself is the thickness of the bowl.
MaxW
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In our world the situation isn't possible - you can't insulate against gravity so there is always gravity acting so the ball has gravitational potential energy.
However, in some other world (not our own), where the situation you describe holds, the ball wouldn't have potential energy; potential energy describes the possibility of motion ie into kinetic energy; in a world where the ball in the bowl cannot possibly move, not even theoretically, but is a wholly fixed element of the world it can't have potential energy; or rather to ascribe potential energy is not meaningful.
Mozibur Ullah
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