`` NEWTON Collisions, Rotations, Negligible Friction
 
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Name: Joe
Status: student
Grade: 9-12
Location: WI
Country: USA
Date: Spring 2014


Question:
Is there any way, by striking it in a off-center direction or other means, to rotate a frictionless sphere on a frictionless surface? I got my AP Physics class and teacher discussing this for a whole period... Most said no because the sphere would slide diagonally off whatever was used to provide the force, but I say that the Force itself, not the friction around the outside of the sphere, would cause a torque due to its off-center direction.

Replies:
Hi, Joe

In my opinion, without friction, you can only apply force to the sphere that is normal to the surface. In the case of a sphere, "normal to the surface" means that the force vector passes through the center. As a result, I do not believe it would be possible to rotate the sphere.

Best regards, Bob Zwicker


No, you cannot rotate a frictionless sphere by hitting it off center. However you strike the sphere, only the component normal to the surface has any effect on the sphere's motion.

Tim Mooney


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