How Do Car Wheels Experience Motion and Inertia?

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Discussion Overview

The discussion revolves around the motion and inertia of car wheels, specifically examining the behavior of points on the wheel as it rotates and moves forward. Participants explore concepts of relative motion and the dynamics involved in the wheel's interaction with the ground.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant suggests that every point on a car wheel is stationary for a brief moment as the wheel rotates, questioning whether this point remains still or moves with the wheel.
  • Another participant emphasizes that "still" is a relative concept, noting that motion is dependent on the frame of reference.
  • A different participant describes the dynamics at the point of contact between the wheel and the ground, stating that this point is pushing the car forward and may have varying velocities depending on conditions like slipping or stretching.
  • It is proposed that the point of contact is stationary relative to the road but not relative to the car itself, highlighting the complexity of motion in different frames of reference.

Areas of Agreement / Disagreement

Participants express differing views on the nature of motion and the behavior of points on the wheel, indicating that multiple competing perspectives remain without a clear consensus.

Contextual Notes

Discussions involve assumptions about relative motion and the definitions of "still" and "velocity," which may not be fully resolved within the conversation.

Curly_810
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Hello I know this sounds stupid but my friend told me about something that made me think. So what he told me was that every point on a car wheel is still for a very small fraction
of time

ImageUploadedByPhysics Forums1395443479.326283.jpg


Point x is stationary at this point in time but as the wheel moves forward it revolves around x and stays at place y

ImageUploadedByPhysics Forums1395443887.692809.jpg


So it looks like this
ImageUploadedByPhysics Forums1395443973.719997.jpg


Does it do this or does it move with the rest of the wheel ?
 
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"Still" is a concept involving motion. Motion is a relative phenomenon. EVERYTHING is still relative to its own frame of reference and anything in that frame of reference. When you a running down the street, you are standing still relative to your belt buckle.
 
The part of the wheel in contact with the ground is pushing the car forward. It is going slightly backward if the tire slips or stretches at all. At the top, the wheel is going forward. So somewhere in between, very near the bottom, it's forward velocity must be zero. You could reasonable say that it has zero velocity exactly at the bottom. But if you want to be really picky, its forward velocity may not be exactly at the bottom and it might have some downward velocity there. In other words, its forward velocity may not be zero at the exact same time that its downward velocity is zero.
 
You could also say that that point is still relative to the road but not to the car
 

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