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Physics/Potential Energy

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Question
Sir,
I've got a few confusions while I was going through my book regarding potential energy. First I don't understand why it can change only to kinetic energy. Then we have a statement that gravitational potential energy is negative and minimum at the surface of the earth. Please help me out.

Answer
Potential energy can be changed into all sorts of energy, so I'm not sure what you're talking about.  There's such a thing as electric potential energy, after all.  Any force can have a potential energy associated with it, because that force can be turned into energy when whatever quantity that force acts on moves along the direction of the force.  The choice of a sign has to do with whether we're going with or against the force, but it's not minimum at the Earth's surface at all...you can drill into the Earth and still go lower in potential energy.

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Dr. Stephen O. Nelson

Expertise

I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.

Experience

I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

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Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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