`` NEWTON Collisions, Rotations, Negligible Friction
Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page Visit Our Archives Ask A Question How To Ask A Question Question of the Week NEWTON Teachers Our Expert Scientists Volunteer at NEWTON! Referencing NEWTON Frequently Asked Questions About Ask A Scientist About NEWTON Education At Argonne Collisions, Rotations, Negligible Friction

Name: Joe
Status: student
Grade: 9-12
Location: WI
Country: USA
Date: Spring 2014

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.

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

Click here to return to the Physics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

Educational Programs
Building 223
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: November 2011
Weclome To Newton

Argonne National Laboratory