What is the Direction of Frictional Force in Pure Rolling?

Click For Summary

Homework Help Overview

The problem involves a wheel of radius 20 cm moving on a rough horizontal surface, where the relationship between linear and angular motion is analyzed in the context of frictional forces during pure rolling. The original poster explores the direction of the frictional force acting on the wheel.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to determine the direction of the frictional force by analyzing the conditions of pure rolling and the distances involved. Some participants question the assumptions made regarding static versus kinetic friction and the implications of the wheel's motion.

Discussion Status

The discussion is active, with participants exploring the implications of the wheel's slipping motion and the corresponding direction of friction. There is a recognition of the need to reconsider initial assumptions about the nature of friction in this scenario.

Contextual Notes

Participants are considering the effects of uniform linear and angular accelerations, as well as the distinction between static and kinetic friction in the context of the problem. The original poster's conclusion about the direction of friction is challenged based on the observed motion of the wheel.

utkarshakash
Gold Member
Messages
852
Reaction score
13

Homework Statement


A wheel of radius 20cm is pushed to move it on a rough horizontal surface. It is found to move through a distance of 60cm on the road during the time it completes one revolution about the centre. Assume that the linear and the angular accelerations are uniform. The frictional force acting on the wheel by the surface is
a)along the velocity of the wheel
b)opposite to the velocity of the wheel
c)perpendicular to the velocity of the wheel
d)zero

Homework Equations



The Attempt at a Solution


Let us suppose that the friction is static and thus pure rolling occurs. The friction will act in the forward direction ie along the direction of velocity.
Since pure rolling occurs
[itex]v=\omega r[/itex]
The angular displacement is 2∏ rad
The perimeter of the wheel is 2∏*0.2 metres
Since pure rolling occurs the linear distance covered should be equal to (2∏*0.2)metres as only one revolution occurs. But the actual linear distance covered is 0.6 m. This means that our assumption is incorrect and thus kinetic friction acts in the backward direction. So answer should be (b) but it is (a). Where is the fault?
 
Physics news on Phys.org
The wheel is being driven (presumably by an axle) but it is 'slipping'. Think about the point where the wheel is in contact with the ground.
Which way is it sliding?
 
AJ Bentley said:
The wheel is being driven (presumably by an axle) but it is 'slipping'. Think about the point where the wheel is in contact with the ground.
Which way is it sliding?

It must be sliding backwards.
 
If it's sliding backwards, which way is the friction?
 
AJ Bentley said:
If it's sliding backwards, which way is the friction?

It must be forward which is the correct answer. Thanks!
 

Similar threads

  • · Replies 7 ·
Replies
7
Views
2K
Replies
24
Views
3K
Replies
4
Views
3K
  • · Replies 42 ·
2
Replies
42
Views
4K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 33 ·
2
Replies
33
Views
1K
  • · Replies 60 ·
3
Replies
60
Views
5K
Replies
13
Views
2K
  • · Replies 8 ·
Replies
8
Views
1K
Replies
61
Views
4K