Rear Wheel Friction: Cycling on an Incline

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SUMMARY

The direction of friction on the rear wheel of a bicycle moving down an incline varies based on whether the cyclist is pedaling. When pedaling, the frictional force acts forward on the rear tire, opposing the tendency of the tire to slip backward due to the bike's acceleration. Conversely, when not pedaling, a small backward force from the road acts on the rear tire to maintain wheel rotation as the bike descends. Understanding these dynamics is crucial for grasping the principles of motion and friction in cycling.

PREREQUISITES
  • Basic understanding of Newton's Third Law of Motion
  • Familiarity with the concepts of friction and rolling resistance
  • Knowledge of bicycle mechanics, particularly regarding wheel dynamics
  • Understanding of incline effects on motion
NEXT STEPS
  • Research the principles of friction in cycling, focusing on rear wheel dynamics
  • Study the effects of incline on bicycle performance and handling
  • Explore Newton's Laws of Motion in the context of cycling
  • Investigate rolling resistance and its impact on cycling efficiency
USEFUL FOR

Cyclists, physics students, and mechanical engineers interested in the dynamics of bicycle motion and the effects of friction on performance.

paras02
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1. Pls tell me the direction of friction on the rear wheel of a cycle moving down on an incline plane in both the cases that are when cycle is being paddled and without any paddling ?
 
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Is the cycle moving without any pedalling
 
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paras02 said:
1. Pls tell me the direction of friction on the rear wheel of a cycle moving down on an incline plane in both the cases that are when cycle is being paddled and without any paddling ?

What is your answer to this question if there is no incline?
 
Chestermiller said:
What is your answer to this question if there is no incline?
when pedalling in forward and when not pedalling in backward
 
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Paddling is moving a boat using a paddle.

A bicycle is moved by turning it's pedals so the word is pedalling.
 
Oops sorry
 
Since we're dealing with words... The word is its, in the context of its pedals! There should be no apostrophe, either in English English or in American English.

I think you can get a good intuitive feel for the forces on the wheel by imagining that you're riding the bike on layers of paper which can slide over each other if the tangential stress is above a certain value. If you're pedalling the bike hard and the paper starts to slip, it will slip backwards - visualise it or try it - because of the frictional force from the back tyre (tire). So the paper (or, without paper, the road surface) will exert a forward force on the tyre (Newton's Third Law). This is the force that accelerates the bike, or, if moving at a steady speed, balances the backwards force of air resistance on the bike.

But (you might argue) doesn't friction always oppose motion? Not exactly. It opposes relative motion between surfaces. The bottom of the back tyre is trying to slip backwards on the road, when you're pedalling. The frictional force on the bottom of the back tyre is therefore forwards.

When you're not pedalling there is a small backwards force from the road acting on the bottom of the tyre. To understand why, remember that there is a small frictional torque opposing the turning of the wheel. In order to keep the wheel turning as the bike descends the hill, there must be a small backwards force on the bottom of the back tyre.

Hope this helps.
 
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There is a Newton third law pair of forces involved with friction. The direction of friction depends if you mean the force the tire's contact patch exerts on the surface of the incline, or the force that the surface of the incline exerts on the tire's contact patch.
 
Thank you guys
 
  • #10
hi paras02! :smile:

"In particular, the friction from the road on the driving or braking wheels of a car is in the same direction as the acceleration or braking, but the friction on the non-driving or non-braking wheels of a car is in the opposite direction."

see the pf library on direction of friction for more detail :wink:
 
  • #11
tiny-tim said:
"In particular, the friction from the road on the driving or braking wheels of a car is in the same direction as the acceleration or braking, but the friction on the non-driving or non-braking wheels of a car is in the opposite direction."
"Friction" or "rolling resistance" for the non-driving tires? There is some friction force at the axles of the non-driving wheels (but that is effectively a small amont of braking), which will also mean some friction force at the tires.
 
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