Why does friction create rolling?

Question

Consider a round object given a push at the middle. The push generates linear velocity, and If there wasn't any friction, the object would start sliding; but the friction in the contact point with the ground causes the object to start rolling.

Intuitively I can explain it: the friction causes the linear speed of the contact point to diminish, and since the other parts of the object still move in the same velocity, rolling is created.

But could somebody provide me with a more thorough physical explanation of what actually happens when the object starts rolling?

Thank you.

Answer 1

You have two non-coincident forces acting on the object: the vector sum of your 'push' force and the object's weight force acting at the middle and the vector sum of the friction force and normal reaction force acting at the periphery.

These forces constitute a force couple (torque) acting on the object which will cause it to rotate.