physics- negative potential energy?

Question

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An object is said to have a negative potential energy. Because it is preferable not to work with negtative numbers, how can you change the value of the objects potential energy without moving the object?

Answer 1

We simply change the coordinates so that PE' > 0.

Example: Suppose you are given PE = -mgh. As m and g are both > 0, this means h < 0. So we simply shift h upward by some H; so that h' = H - h > 0. Now, PE' = mgh' > 0.

Although we've taken care of potential energy, which is now positive for ease of working, we have to remember we added H to all vertical dimensions in the problem. For instance, if y is the vertical dimension of some point p(x,y) in your problem with PE, the translated point is p'(x,y + H) = p'(x,y') as you work the problem.

Once you've found PE', you then need to re-translate it back to PE, in the original coordinates, from PE' = mgh' = mg(H - h) = mgH - mgh = mgH + PE = PE'; so that, PE = PE' - mgH < 0 once again.

Answer 2

Negative Potential Energy

Answer 3

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Kinetic energy is almost never negative, because people tend to place the zero where v=0. Potential energy, however, is only defined up to an additive constant -- for any potential energy function U, there's no physical difference between the functions U(x,y,z,t) and U(x,y,z,t) + u, where "u" is a constant. So, for example, if you're studying the gravitational potential energy close to Earth's surface, you probably choose the energy to be zero at the ground, and then you never go negative because you never go underground. But if you instead want to study gravitational potential energy in the solar system, you probably want to choose the value to be zero at infinity. In which case, the entire gravitational potential field is negative, everywhere.

Answer 4

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RE:
physics- negative potential energy?
Yes, this is homework help...

An object is said to have a negative potential energy. Because it is preferable not to work with negtative numbers, how can you change the value of the objects potential energy without moving the object?

Answer 5

I assume you mean gravitational potential energy.

If you cannot move the object, move the source of the gravitaional field in which the object is in. The further away you move the source away, the less negative the potential energy becomes.

Thinking abstractly, you can choose a point behind the object as infinity, since gravitational potential is the work done against gravity when an object is moved from infinity to that point, and gravity is an attractive force, such an object can be considered to be at positive potential energy by this definition since you choose to put it beyond infinity.

Answer 6

Because only the gradient of the potential and differeces in potential appear in physical problems, you may add ANY constant to the potential you wish and not change the dynamics in any way. So change V to V + 2000J. Everything works the same as it did before, but you've raised the potential by 2000J.

Answer 7

There is no such thing as an object with negative energy, potential energy of an object is always positive.

Since PE=mgh, an object's potential energy can be decreased by decreasing either its height h or mass m (g cannot be decreased because gravity is constant on Earth).

Answer 8

What's wrong with negative numbers???