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# Gravitational/Electrical Potential (Energy) watch

1. Hey, I have AQA Physics Mod4 on Thursday and I still don't understand Gravitational and Electrical Potential. I can't quite grasp what they are measuring and what they actually mean. Can anyone help me out? This is the only thing I can't quite get, even though people have tried to explain to me many times.

2. Think of it like a hill. If I stand at the top of a hill, I could roll down it and in doing so gain some kinetic energy. It could be said then that at the top of the hill that I have the opportunity, or potential, to gain some kinetic energy. I can work out how much kinetic energy I could gain by looking at the height of the hill and knowing my mass, so I can quantify the amount of energy I could gain if I were to roll down it. This energy I could gain is energy I can potentially have, hence it is referred to as potential energy.

A potential is therefore a measure of how much energy something could potentially convert to another form by moving from one point in a field to another. (field being gravitational or electrical in this case). Going from the top to bottom of a hill of height h allows me to convert mgh of gravitational potential energy into kinetic energy, meaning that at the top of the hill the gravitational potential is mgh relative to that at the bottom.

Potentials always need two points of reference to make sense - you need to be able to say 'if I move from here to there, I will gain/lose this much energy'. One point can be at infinity, but two points are always required.

Does this clear it up for you?
Think of it like a hill. If I stand at the top of a hill, I could roll down it and in doing so gain some kinetic energy. It could be said then that at the top of the hill that I have the opportunity, or potential, to gain some kinetic energy. I can work out how much kinetic energy I could gain by looking at the height of the hill and knowing my mass, so I can quantify the amount of energy I could gain if I were to roll down it. This energy I could gain is energy I can potentially have, hence it is referred to as potential energy.

A potential is therefore a measure of how much energy something could potentially convert to another form by moving from one point in a field to another. (field being gravitational or electrical in this case). Going from the top to bottom of a hill of height h allows me to convert mgh of gravitational potential energy into kinetic energy, meaning that at the top of the hill the gravitational potential is mgh relative to that at the bottom.

Potentials always need two points of reference to make sense - you need to be able to say 'if I move from here to there, I will gain/lose this much energy'. One point can be at infinity, but two points are always required.

Does this clear it up for you?
Ok, that makes more sense. But, why would the Potential be a minus then? And what's the difference between for example, Gravitational Potential and Gravitational Potential Energy?
4. Ok, that makes more sense. But, why would the Potential be a minus then? And what's the difference between for example, Gravitational Potential and Gravitational Potential Energy?
Gravitational potential energy is given by

It is negative due to the way it is defined. Gravitational potential energy is defined as being 0 at an infinite distance from an object. An object coming in from infinity towards a mass will gain kinetic energy (it is effectively falling toward this mass). Energy must always be conserved, so to make this true the gravitational potential energy needs to be negative to compensate for the gain in kinetic energy. e.g. gain in KE = loss of GPE.

The gravitational potential of a point is defined as the potential energy a unit mass (i.e. 1kg) would have at a given point r in a gravitational field caused by a mass M. It's given by

It allows each point in space to be assigned a definite gravitational potential value, which is independent of the mass m of an object sitting there.
5. Also maybe check this link out

http://www.sparknotes.com/physics/gr.../section1.html

Bit of a clearer explanation than mine!

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Updated: January 26, 2010
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