cylinder on a frictionless inclined plane

[jp]

I just have a question about cylinder. If a cylinder is on a frictionless inclined plane, does it spin as it comes down? I guess on a level surface, frictional force is required for a cylinder to roll, but I'm not sure about inclined plane.

[Doc Al]

Originally posted by jp
If a cylinder is on a frictionless inclined plane, does it spin as it comes down? I guess on a level surface, frictional force is required for a cylinder to roll, but I'm not sure about inclined plane.
If the cylinder is started from rest, it will just slide down without rolling. A friction force is required to exert the torque needed to start it spinning about its center.

[HallsofIvy]

More precisely, since gravitational force acts on every point of the object, it is the same as if it acted only on the "center of gravity"- since the net force is through the center of gravity there is not torque and so no rotation.

[himanshu121]

Since all the forces are passing through COM and there is no physical interaction due to friction hence it must slide