How can I use the right hand rule to find torque in bicycle wheel rotation?

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Homework Help Overview

The discussion revolves around the application of the right hand rule in determining torque during the rotation of a bicycle wheel. Participants explore the relationship between applied forces, friction, and the resulting motion of the wheel.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the importance of friction in relation to the applied force and whether the wheel slips or not. There are inquiries about how to represent forces in a free body diagram and the implications of different scenarios on torque calculations.

Discussion Status

The discussion is active with participants questioning assumptions about friction and its direction. Some have provided guidance on drawing free body diagrams and considering different scenarios, while others are clarifying the relationship between applied forces and frictional forces.

Contextual Notes

There is an assumption that the wheel does not slip, which influences the discussion on the direction of friction and the resulting motion of the wheel. Participants are also navigating the complexities of how to visualize and represent these forces accurately.

ReCryptic
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Homework Statement
Suppose you stand up a bicycle wheel and push on its lower spoke in the direction shown which way will it roll? Explain your reasoning and assume there is friction
Relevant Equations
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image.jpg

I tried to use the right hand rule to find torque but I’m not sure to go from there.
 
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Do you think it matters if the applied force is enough to overcome the friction and make the tire slide?
 
Hi ReCryptic. Do free body vector diagram showing all the forces at the moment you apply force.

There are at least a couple of possible scenarios:
1. Where the friction force on the tire does not allow the wheel to slip.
2. Where the friction force on the tire is insufficient to overcome the applied force of your hand and the tire moves relative to the surface.

The torques on the wheel will depend on where on the spoke you apply the force. So you will need to identify where the applied force is located (i.e. distance to hub and distance to surface) to work out the torques. hint: the right hand rule to work out the torque directions is really not that important for this question.

AM
 
phinds said:
Do you think it matters if the applied force is enough to overcome the friction and make the tire slide?
I think we are supposed to assume that the wheel doesn't slip.
 
Andrew Mason said:
Hi ReCryptic. Do free body vector diagram showing all the forces at the moment you apply force.

There are at least a couple of possible scenarios:
1. Where the friction force on the tire does not allow the wheel to slip.
2. Where the friction force on the tire is insufficient to overcome the applied force of your hand and the tire moves relative to the surface.

The torques on the wheel will depend on where on the spoke you apply the force. So you will need to identify where the applied force is located (i.e. distance to hub and distance to surface) to work out the torques. hint: the right hand rule to work out the torque directions is really not that important for this question.

AM
How do I know which direction friction is if I don’t know the direction of motion?
 

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ReCryptic said:
How do I know which direction friction is if I don’t know the direction of motion?
Well, you just said to assume that it doesn't slip so how many directions are left?
 
phinds said:
Well, you just said to assume that it doesn't slip so how many directions are left?

So then friction has to be towards the left.

The wheel rotates clockwise because the force is applied to the left and friction acts opposite to that applied force. Am I right?
 
ReCryptic said:
How do I know which direction friction is if I don’t know the direction of motion?
Friction does not simply "oppose motion". It opposes relative motion of the surfaces in contact.
See https://www.physicsforums.com/insights/frequently-made-errors-mechanics-friction/
Without friction, what would be the relative motion of those surfaces? Which way must friction act on the tyre to prevent that?
 
ReCryptic said:
So then friction has to be towards the left.

The wheel rotates clockwise because the force is applied to the left and friction acts opposite to that applied force. Am I right?
?
You just said that the friction force acts towards the left AND the force applied acts to the left (despite showing a hand pushing to the right).
 
  • #10
phinds said:
?
You just said that the friction force acts towards the left AND the force applied acts to the left (despite showing a hand pushing to the right).
I just realized I typed that wrong. The force is applied to the right and friction acts to the left.
 
  • #11
phinds said:
?
You just said that the friction force acts towards the left AND the force applied acts to the left (despite showing a hand pushing to the right).
@ReCryptic may have meant "applied to the left" in the sense of being applied on the left, i.e. the point of application is to the left of the wheel.
 
  • #12
ReCryptic said:
I just realized I typed that wrong. The force is applied to the right and friction acts to the left.
In that case, yes you have it right in post #7
 
  • #13
haruspex said:
Friction does not simply "oppose motion". It opposes relative motion of the surfaces in contact.
See https://www.physicsforums.com/insights/frequently-made-errors-mechanics-friction/
Without friction, what would be the relative motion of those surfaces? Which way must friction act on the tyre to prevent that?
Without friction, the wheel would just slip on the surface, but not really move.
 
  • #14
ReCryptic said:
Without friction, the wheel would just slip on the surface, but not really move.
It would not rotate, but the surfaces in contact would slide past each other. Which way would the wheel slide? Which direction must the frictional force be to prevent that?
 
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  • #15
Wouldn't the wheel slide towards the right? Then friction would have to act towards the left.
 
  • #16
ReCryptic said:
Wouldn't the wheel slide towards the right? Then friction would have to act towards the left.
Yes.
 
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  • #17
haruspex said:
Yes.
Okay thank you.
 

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