# Rotational motion & Incline Plane

## Main Question or Discussion Point

Hello everybody. I have a rather strange question regarding the rotational motion of a solid object across an incline plane. I wonder if it is possible for a solid object to move upwards the plane without the application of any external force, other than its own weight and the friction with the plane. It goes without saying that the object is not thrown across the plane. We just leave it at some point and instead of going downwards as it should this moves upwards. If anyone has any ideas on the subject i would like to hear them. Thank you.

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Hootenanny
Staff Emeritus
Gold Member
Hello everybody. I have a rather strange question regarding the rotational motion of a solid object across an incline plane. I wonder if it is possible for a solid object to move upwards the plane without the application of any external force, other than its own weight and the friction with the plane. It goes without saying that the object is not thrown across the plane. We just leave it at some point and instead of going downwards as it should this moves upwards. If anyone has any ideas on the subject i would like to hear them. Thank you.
No, it is impossible; it would violate conservation of energy and momentum at the very least.

P.S. Are you being serious? :surprised

P.P.S. Welcome to the forums.

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It seems plausible to me. There is no conservation of momentum when you have an external friction force Hoot.

An orbital sander will dance across the floor if you turn it on and just leave it there.

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Hootenanny
Staff Emeritus
Gold Member
Okay, momentum was bad idea, but seriously cyrus, can you see this happening?

regarding the rotational motion of a solid object across an incline plane. I wonder if it is possible for a solid object to move upwards the plane without the application of any external force, other than its own weight and the friction with the plane. [..] We just leave it at some point and instead of going downwards as it should this moves upwards.
No, it is impossible
How about an unbalanced wheel? If placed so, then it will roll such that it moves a short distance up the incline.

Heck, an ordinary car can be driven up an incline with no external force other than it's own weight and the friction with the ground.

Integral
Staff Emeritus
Gold Member
Tape a weight to the inner side of a tin can, now place the can on the inclined plane so the weight is biased to the upper side of the inclined plane. The can will roll up the slope.

Tape a weight to the inner side of a tin can, now place the can on the inclined plane so the weight is biased to the upper side of the inclined plane. The can will roll up the slope.
Ladies and gentleman, we have a winner . That was a good one!

Even when I see it, I say noooooooo that cant be right. It looks so unnatural. :rofl:

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That's right. It has to do with the position of the CM of the body. As far as momentum and energy conservation laws, none of them are violated since this is not an isolated system and since the CM is higher than normal we have gravitational energy converting to kinetic. Thank you.

Hootenanny
Staff Emeritus