Acceleration of point of contact

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Discussion Overview

The discussion revolves around the acceleration of the point of contact of a sphere undergoing pure rolling on a smooth surface, with the center of mass moving at a constant velocity. Participants explore various aspects of the motion, including the relationship between linear and angular quantities, and the nature of acceleration in this context.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants assert that the velocity of the point of contact during rolling motion is zero.
  • Others question whether the acceleration of the point of contact should consider centripetal acceleration, suggesting it is relevant to the overall analysis.
  • There is a proposal that the relationship between the center of mass velocity and angular speed can be expressed mathematically, with some participants suggesting that the acceleration of the center of mass is zero in uniform rolling.
  • Some participants argue that the acceleration of the point of contact is directed towards the center of mass, regardless of whether the rolling is uniform or accelerated.
  • There is a discussion about the implications of different interpretations of the term "point of contact," leading to varied conclusions about its acceleration.
  • One participant notes that the original question lacks clarity, leading to different interpretations and answers regarding the acceleration of the point of contact.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the nature of the acceleration of the point of contact. There are multiple competing views regarding whether to consider linear acceleration, centripetal acceleration, or both, and the implications of the question's phrasing contribute to the disagreement.

Contextual Notes

The discussion highlights limitations in the clarity of the original question, which affects the interpretations and responses provided by participants. There is also a dependence on definitions of terms like "point of contact," which leads to varied conclusions.

  • #31
quawa99 said:
For a sphere undergoing pure rolling on a smooth surface with center of mass having constant velocity,what is the acceleration of point of contact

You've got different answers because your question isn't clear. What do you mean by "point of contact"? Three possible interpretations and related answers:

1) a virtual point that moves along the surface so as to coincide always with the surface's point that touches the sphere. Its speed is constant, so it's acceleration is zero.

2) the material point of the flat surface that, at a given instant, touches the sphere. It does not move: speed zero, acceleration zero.

3) the material point of the sphere's surface that, at a given instant, touches the flat surface. This is the most interesting case. Its trajectory is an ordinary cycloid, its instantaneous speed is zero, however, its acceleration is the centripetal acceleration it had if the sphere were only rotating (no translation) around the same axis with same angular speed. Can you see why?

--
TRu-TS
Buon vento e cieli sereni
 

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