# Trouble understanding what rolling friction is

• B
• tbn032
In summary, static friction opposes the motion of the sphere being applied to the contact points. It is applied when the sphere is rolling on a flat surface. The sphere deforms, and so the normal forces are shifted to the right from the center of mass.
tbn032
In pure rolling the of the sphere contact points of the sphere are at zero velocity,how is friction opposite to the motion of sphere being applied to these points?how the frictional force f is bieng applied to the sphere?

If the sphere is simply rolling on a flat surface, then the frictional force must be zero because there is no acceleration. F = m a

malawi_glenn
The sphere which is rolling is not a perfect rigid body, and thus it deforms. Thus the normal forces is shifted to the right from center of mass.In my book, it is written that 3 forces are acting on the sphere.
A)weight mg
B)friction at contact
C)the normal force
I am confused about the friction at contact force. How is it being applied?

can you please explain what exactly is rolling friction?

What is the book title and author?

Concepts of physics 1,HC verma

Lnewqban
Rolling static friction can exist when there is no rotation or movement.
For example, the driving wheels of a locomotive, trying hard to start movement of heavy cars, but without slipping on the rails.

Not a very scientific approach, but I like explaining rolling static friction like being partially similar to the mechanical teeth meshing that happens in a rack and pinion mechanism.
At microscopic level, that is aproximately the interaction that happens among two rough surfaces, in addition to molecular attraction.

The deformation of the surfaces that the book explains, will contribute to the resistance to rolling, but I believe that it is not related to pure static friction.
There is not much at all of that deformation among the steel wheels and hard steel of the rails in my previous example, yet, friction makes the heavy cars move finally.

russ_watters
Lnewqban said:
Rolling static friction
Do you have a definition in mind for "rolling static friction". I do not know what you mean by that phrase.

Certainly there can be static friction between an unmoving wheel and the ground upon which it rests.

jbriggs444 said:
Do you have a definition in mind for "rolling static friction". I do not know what you mean by that phrase.

Certainly there can be static friction between an unmoving wheel and the ground upon which it rests.
I see it as the instantaneous non-slipping contact of a rolling body against another surface, flat or not, when a torque is present.
Once the limit of adherence if exceeded, it becomes “rolling dynamic friction” in my mind, if some rolling of the body remains.

## What is rolling friction?

Rolling friction is a type of friction that occurs when an object rolls over a surface. It is caused by the deformation of the object and the surface, and the energy lost in this process is known as rolling resistance.

## How is rolling friction different from other types of friction?

Rolling friction is different from other types of friction because it involves the movement of an object over a surface, rather than the sliding or rubbing of two surfaces against each other. This type of friction is typically lower than other types of friction, such as static or kinetic friction.

## What factors affect the amount of rolling friction?

The amount of rolling friction is affected by several factors, including the weight and shape of the object, the type of surface it is rolling on, and the speed at which it is rolling. The type of material the object and surface are made of can also impact rolling friction.

## How is rolling friction measured?

Rolling friction is typically measured using a device called a tribometer, which applies a known force to an object and measures the resistance as it rolls over a surface. The coefficient of rolling friction, which is the ratio of the force applied to the force of the object's weight, is used to quantify the amount of rolling friction.

## How can rolling friction be reduced?

There are several ways to reduce rolling friction, including using smoother surfaces, reducing the weight of the object, and using lubricants or ball bearings. Additionally, increasing the speed of the rolling object can also decrease the amount of rolling friction.

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