Conservation of energy in a wheel

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Homework Help Overview

The discussion revolves around the conservation of energy in the context of a wheel rolling without slipping on a plane. Participants are exploring the implications of static friction and its role in energy conservation.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants are questioning whether the static friction force does any work and how that affects energy conservation. There is confusion about the nature of static friction and its impact on the system, particularly regarding the changing point of action of the force.

Discussion Status

The discussion is ongoing, with some participants providing insights into the relationship between static friction and energy conservation. There is acknowledgment of the complexities involved, particularly regarding rolling resistance and its distinction from friction.

Contextual Notes

Participants are grappling with the definitions and implications of static friction, work done by forces, and the conditions under which energy is conserved or not. The discussion reflects a mix of theoretical understanding and practical considerations in the context of rolling motion.

paalfis
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Homework Statement


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A wheel rolls without slipping on a plane, what magnitudes are conserved?


The Attempt at a Solution

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I don't know if the static friction force does any work. Energy won't be conserved if it does.
 
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Friction is a force between two surfaces in contact. When a force does work, what equation tells you how much work is done?
 
Linear integral of scalar product between force and the direction of motion. But does THIS force does any work? Because after all, it is static, but its point of action is changing with time, that is my confusion.
 
paalfis said:
Linear integral of scalar product between force and the direction of motion. But does THIS force does any work? Because after all, it is static, but its point of action is changing with time, that is my confusion.
The force is 'trying' to move the surfaces in relation to each other. Does it succeed?
 
No it doesn't. Ok, so energy is conserved. Energy won't be conserved if there is any slipping between the surfaces, correct?
This is not so intuitive to me because I think static force as 'pressure' applied by each body to the other body, somehow using energy to change the molecular state of the other body's structure, why is this wrong?
 
paalfis said:
Energy won't be conserved if there is any slipping between the surfaces, correct?
Correct.
paalfis said:
I think static force as 'pressure' applied by each body to the other body, somehow using energy to change the molecular state of the other body's structure
There is some truth in that. In the case of a rolling wheel, there are losses associated with the deformation of the road and wheel as the load shifts. But this is referred to as rolling resistance, not friction. It is generally ignored in 'school', in the same way that air drag is ignored in most ballistics questions.
 

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