Why does friction create rolling?

[giladbr]

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.

 

[Astronuc]

The friction at the edge (surface) applies a moment (force at distance from rotational axis or center of mass) which induces a torque, which induces a change in angular momentum of the mass about the rotational axis.

 

[baba89]

I can provide a more detailed explanation of why friction creates rolling. When an object is given a push at the middle, it starts to rotate due to the torque applied by the push. This rotation creates a linear velocity at the contact point between the object and the ground. However, without friction, this linear velocity would not be enough to overcome the inertia of the object and it would simply slide on the ground.

Friction, on the other hand, acts in the opposite direction of the linear velocity, creating a force that opposes the motion of the object. This force acts on the contact point between the object and the ground, causing it to slow down. As a result, the linear velocity at the contact point decreases, while the rest of the object continues to rotate at the same speed. This difference in velocities creates a torque that causes the object to roll forward.

In other words, friction converts the linear motion at the contact point into rotational motion, allowing the object to roll. This is because the frictional force creates a torque that acts on the object's center of mass, causing it to rotate. This rotational motion, combined with the linear velocity at the contact point, allows the object to move forward in a rolling motion.

Furthermore, the shape of the object also plays a role in creating rolling. A round object has a smaller surface area in contact with the ground compared to a flat object, which means there is less friction acting on it. This allows the object to roll more easily as the frictional force is not strong enough to completely stop the rolling motion.

In summary, friction creates rolling by converting linear motion into rotational motion, allowing the object to move forward in a rolling motion. Without friction, the object would simply slide on the ground.