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

In summary: No, the wheel would not slide because there is no forward motion. It would just rotate in place. The direction of friction would be towards the left to prevent the wheel from sliding forward. In summary, the conversation discusses using the right hand rule to find torque and the importance of identifying the location of the applied force to determine the torques on the wheel. They also mention the direction of friction and its role in preventing the wheel from sliding.
  • #1
ReCryptic
11
0
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
N/A
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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  • #2
Do you think it matters if the applied force is enough to overcome the friction and make the tire slide?
 
  • #3
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
 
  • #4
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.
 
  • #5
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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  • #6
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?
 
  • #7
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?
 
  • #8
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?
 
  • #9
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.
 

1. How does the right hand rule work to find torque in bicycle wheel rotation?

The right hand rule is a method used to determine the direction of rotation and torque in a rotating system, such as a bicycle wheel. To use this rule, point your right thumb in the direction of the rotation and curl your fingers around the object. The direction your fingers are pointing is the direction of the torque.

2. What is torque and why is it important in bicycle wheel rotation?

Torque is a measure of the force that causes an object to rotate around an axis. In the case of a bicycle wheel, torque is important because it is what allows the wheel to rotate and move the bike forward. Without torque, the wheel would not be able to turn and the bike would not be able to move.

3. How can I use the right hand rule to determine the torque in a bicycle wheel?

To determine the torque in a bicycle wheel using the right hand rule, simply point your right thumb in the direction of the rotation and curl your fingers around the wheel. The direction your fingers are pointing is the direction of the torque. You can also use this rule to determine the direction of rotation by looking at the direction your thumb is pointing.

4. Can the right hand rule be used to calculate the exact amount of torque in a bicycle wheel?

No, the right hand rule only helps to determine the direction of the torque in a rotating system. To calculate the exact amount of torque in a bicycle wheel, you will need to know the force applied to the wheel and the distance from the axis of rotation.

5. Are there any other methods besides the right hand rule to find torque in bicycle wheel rotation?

Yes, there are other methods that can be used to find torque in bicycle wheel rotation, such as using equations and calculations. However, the right hand rule is a simple and intuitive method that is commonly used in physics and engineering to determine the direction of torque in a rotating system.

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