Friction acting on a wheel that is initially at rest

AI Thread Summary
To start a wheel rolling from rest, static friction is necessary, and the maximum static friction force can be calculated using the equation F = μN. The actual friction force needed depends on the desired acceleration, which can be determined using Newton's second law (F = m*a). For ongoing motion, rolling resistance, not static friction, becomes the opposing force, which is influenced by the wheel's deformation and elasticity. Torque can be calculated for rotational motion using the equation Torque = I*α. Understanding these principles is crucial for selecting the appropriate motor and gearbox for the project.
geko11
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Hello everyone,

I have a project of mine where I need to find out the force that acts on a wheel to start it rolling and keep it rolling so I can then select the correct motor and gear box.

I have not had to do this kind of physics for years and I am having trouble with this problem:

If a wheel is initially at rest then the standard static friction equation would apply (F = u*Normal) initially to find the force to get the wheel moving and then the rolling friction force equation would be used to work out the force required to keep it going?

or

Because it is a wheel the initial and ongoing friction would be determined by using the rolling static friction equation in both cases?

I am really confused here and would really appreciate the help.

Thanks. :)
 
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geko11 said:
If a wheel is initially at rest then the standard static friction equation would apply (F = u*Normal) initially to find the force to get the wheel moving and then the rolling friction force equation would be used to work out the force required to keep it going?
To get the wheel rolling requires static friction (assuming no slipping). But μN gives the maximum amount of friction available to you; the actual friction required depends on the acceleration you are trying to impart. (The actual static friction could be anything from 0 to the maximum value.)
 
ok thanks, so F=uN is max force.

what equation do I use if I have an acceleration in mind to find the force?
 
geko11 said:
ok thanks, so F=uN is max force.
Right.
what equation do I use if I have an acceleration in mind to find the force?
Newton's 2nd law for rotation and translation.
 
F=m*a...
now I feel like an idiot, but I am glad I asked.
thanks doc your a Legend.
 
geko11 said:
F=m*a...
That will do for translation; for rotation, use Torque = I*alpha.
 
rcgldr said:
The opposing force is due to rolling resistance, not static friction.
To accelerate the wheel from rest, static friction is required.
 

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