Rolling friction

We all have seen the vehicles moving on the road.

Some of us have also observed the motion of the wheel of the vehicle.

We have observed that the motion of the wheel is actually the combination of translation and rotation.

we also have observed that the wheels of the vehicles can roll very smoothly on some surfaces.

And sometimes it becomes difficult for the wheels to roll smoothly on some other surfaces.

This change in speed of vehicles and rolling of wheels is due to the surface on which they are rolling.

These surface properties are defined by the roughness and smoothness of the surface that has a definite coefficient of friction.

We also have noticed that if we roll a ball on a surface then it will eventually come to rest. This is due to the rolling friction.

Let's first discuss friction.

Friction is a force. This force holds back the movement of a sliding object. The force acts in the opposite direction to the way an object wants to slide.

In this case, we can understand that the direction of friction, on the block is in backward direction. It tries to stop the block.

But, the same magnitude of friction works on the floor in forward direction during the motion. It tries to move the floor in forward direction.

This friction is also known as translational friction. It always works between two contact surfaces of moving bodies.

Now let's discuss rolling motion and torque.

We know that the rolling is the combination of translation and rotation motion of an object. If an object translates and rotates both at the same time, then it is rolling.

The rolling of a wheel can be illustrated as above.

The rotation of an object is provided by some external torque, so it is also necessary to understand torque.

Consider a rod of length that is acted upon by force, at an angle

The torque on the rod will be provided as above.

If we will look for perpendicular distance on force then it will be and torque will be,

If we want to understand the direction of torque then let's apply right-hand thumb rule, stretch our right hand in the direction of the vector .

If we curl our fingers along the direction vector in such a way that sense of rotation is from and towards .

We find that angular acceleration is acting in the clockwise direction and the direction of torque is clockwise.

The understanding of the direction of torque is very important for understanding the rolling friction.

Now let's discuss rolling friction and the direction of rolling friction.

Let's consider a ball having its center at and rolling on a surface.

Now let's consider an external force acting on the ball and it is rotating with an angular acceleration .

The direction of torque will be clockwise which is responsible for the clockwise angular acceleration.

The torque due to the force will be zero w.r.t. because is passing through the center of ball.

The torque due to force is zero but the ball is having a clockwise torque which will be provided by friction.

The rolling friction, will act in the backward direction to provide clockwise torque w.r.t. point .

The rolling friction is always less than the sliding friction because in rolling only a part of the object comes into contact with the surface.

This is how we can define the rolling friction and direction of the rolling friction depending upon the direction of the torque.

Revision

Friction is simply the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other.

Friction opposes the relative motion of a body and it is dimensionless property.

The friction acting during the rolling on an object against a contact surface is known as rolling friction.

The End