A body only rotates on an inclined plane if it has friction?

[LCSphysicist]

Homework Statement

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Relevant Equations

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I think that the answer probably will be yes, but i have a question:
Well, with respect to center of mass that's right, but if i choose the axis passing through the contact point, the weight force will produce torque, even without the friction.

 

[lewando]

If you "move the axis of rotation to the contact point", it is constrained by the plane so that it cannot rotate. As such, can it really be declared an axis of rotation?

 

[haruspex]

Homework Statement:: .
Relevant Equations:: .

I think that the answer probably will be yes, but i have a question:
Well, with respect to center of mass that's right, but if i choose the axis passing through the contact point, the weight force will produce torque, even without the friction.

Torque about what point, and what shape of body?

If you take the mass centre as the axis, the weight does not produce torque. For a cylinder, the normal force won't either. With no friction, there is no force producing torque.

If you take the point of contact as axis the weight does have torque, so there will be angular acceleration about that point. But linear acceleration of a body constitutes angular acceleration about a point not in its line of motion, so this still does not ensure rotational acceleration.

If the body is not a sphere or cylinder nor lying on a flat face then the normal force might have moment about the mass centre.

 

[LCSphysicist]

Torque about what point, and what shape of body?

If you take the mass centre as the axis, the weight does not produce torque. For a cylinder, the normal force won't either. With no friction, there is no force producing torque.

If you take the point of contact as axis the weight does have torque, so there will be angular acceleration about that point. But linear acceleration of a body constitutes angular acceleration about a point not in its line of motion, so this still does not ensure rotational acceleration.

If the body is not a sphere or cylinder nor lying on a flat face then the normal force might have moment about the mass centre.

" point. But linear acceleration of a body constitutes angular acceleration about a point not in its line of motion, so this still does not ensure rotational acceleration "
I can't get this part, can you say more about this?

 

[haruspex]

" point. But linear acceleration of a body constitutes angular acceleration about a point not in its line of motion, so this still does not ensure rotational acceleration "
I can't get this part, can you say more about this?

Consider a particle moving horizontally with velocity v, height h, mass m. Wrt a point on the ground it has angular velocity vh and angular momentum mvh. Similarly angular acceleration and linear acceleration.