Accelerating a wheel of two different materials.

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Discussion Overview

The discussion revolves around the behavior of a wheel composed of two different materials—metal and wood—when subjected to rotation. Participants explore concepts of acceleration, center of mass, and the potential for wobbling during rotation, particularly when the wheel is constructed from halves of each material.

Discussion Character

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

Main Points Raised

  • Some participants recall an experiment where a hollow metal wheel and a solid wooden wheel of equal mass and dimensions raced down a ramp, noting that the wooden wheel accelerates faster.
  • One participant questions whether a wheel made from halves of each material would balance and how it would behave when rotated, particularly under accelerated and decelerated conditions.
  • Another participant suggests that different accelerations could lead to vibrations at higher RPMs.
  • Some participants agree that the center of mass of the composite wheel would not be at its geometric center, leading to potential wobbling during rolling.
  • A participant draws a parallel to dynamic balancing in automobiles, indicating that similar principles apply to the wheel in question.
  • Technical details are provided regarding the center of mass for solid and hollow semicircles, suggesting that the differing centers of mass for the wood and metal components would prevent the wheel from being balanced.

Areas of Agreement / Disagreement

Participants generally agree that the composite wheel would not balance due to differing centers of mass, but there is no consensus on the specific behavior of the wheel under rotation, particularly regarding wobbling and vibrations.

Contextual Notes

The discussion includes assumptions about the physical properties of the materials and the geometric configurations of the wheel components, which may influence the outcomes described. The implications of acceleration and deceleration on the wheel's stability remain unresolved.

racer123
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We all remember the experiment where two wheels, one made of metal that is hollow and one of solid wood, of equal mass, circumference, and width are raced down a ramp, how the wooden wheel accelerates faster.
If you cut the wheels in half and used one part of each to create another wheel, half metal and half wood, would they balance? What would happen if rotated? And, if the rotation was accelerated and decelerated, would it wobble or would it act in a uniform manner?
Thanks
 
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Your first paragraph answers the second...different accelerations would tend to cause vibrations at higher rpm...
 
That's my understanding as well. I wanted to get the opinion of people that have a far better understanding of physics than I do to confirm it.
 
Its center of mass would not be at its geometric center, so it would wobble around if you let it roll.
 
The concept is the same concept as when a weight is clamped on the rim of a wheel for dynamic balancing on an automobile...
 
The center of mass of a solid semicircle is at distance ##\dfrac{4r}{3\pi} = 0.424 r## from the center. The COM of a semicircular arc is ##\dfrac{2r}{\pi} = 0.637 r## from the center.

The "hollow" metal half is not exactly a semicircular arc, but it should be clear the COM's of the two equal masses of wood and metal wlll be at different distances about the center, and the wood+metal disc will not be balanced.
 

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