Trouble understanding what rolling friction is

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  • #1
tbn032
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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?
20220819_105439.jpg
 

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  • #2
Baluncore
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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
 
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  • #3
tbn032
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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?
 
  • #4
tbn032
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can you please explain what exactly is rolling friction?
 
  • #5
Baluncore
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What is the book title and author?
 
  • #6
tbn032
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Concepts of physics 1,HC verma
 
  • #8
Lnewqban
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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.

Rack-pinion-Gear-wheel-cogwheel.gif
 
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  • #9
jbriggs444
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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.
 
  • #10
Lnewqban
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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.
 

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