# Physics Discussiom questions

$1$A ball rolls without slipping on a perfectly flat plane of infinite extent. Will it roll forever? If not, what would stop it?

$2$ Since only changes in potential energy are important in any problem, a student decides to let the elastic potential energy of a spring be zero when the spring is stretched a distance of x1. The student decides therefore to let U={1/2}k(x-x1)^2. Is this correct?”)

$3$.would space be effected by infinite amount of gravity? we know space has no mass and this might be a wrong question to ask. space is expanding because of dark energy, can it contract because of an infinite amount of gravity. ) -(This is not my homework just discussion question I found) Note by Mardokay Mosazghi
6 years, 3 months ago

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1 the ball will stop because of friction

3 scientist also thik that universe will colapse because of graviti of every galaxy but it is not happening so the energy  that is acting in the univers Is known as dark energy because we dont know about it

- 5 years, 12 months ago

1.Yes because of gravity

- 6 years, 3 months ago

1. Rolling resistance would stop it. In short, the net normal force will not act exactly on the center of mass and would produce a small torque which would eventually stop the ball rolling.

2. No, its a baseless assumption. The given formula is derived by integrating very small potential energies and is only valid when spring's initial position is at x = 0.

3. No I think the space would expand. Is there any special reason why you have chosen infinite gravity? You could have simply asked if gravity would conract the space or not. Why infinite gravity my friend?

Ask if you doubt any of this.

New Question 4: What would be the direction of frictional force on a rolling without slipping ball? And why? If you think it's in the backward direction, why don't the ball accelerates? If you think it's in front direction why don't the ball disaccelerates like a cube if thrown forward with the same speed?

- 6 years, 3 months ago

I don't seem to find the answer do you know the answer

- 6 years, 3 months ago