Finding Velocity of Particle at Wheel Edge

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Discussion Overview

The discussion revolves around determining the velocity of a particle located at the edge of a rolling wheel, specifically addressing the relationship between the center of mass velocity and the velocity of points on the wheel's circumference. The scope includes mathematical reasoning and conceptual clarification regarding the application of rotational motion principles.

Discussion Character

  • Mathematical reasoning
  • Conceptual clarification

Main Points Raised

  • One participant states that due to the rolling constraint, the velocity of the center of mass (V(cm)) is equal to R*w, where w is the angular velocity.
  • The same participant expresses confusion about calculating the velocity of a specific point on the wheel, particularly at the front edge, and mentions consistently arriving at 2wR, which they recognize as the velocity at the top of the wheel.
  • Another participant clarifies that the velocity of a particle relative to the center of mass is a vector, with its magnitude given by ωR and direction tangent to the wheel, leading to a derived velocity of √2 V for the front edge when combined with the center of mass velocity.
  • A later reply suggests that to find the velocity of a point at an arbitrary location on the wheel, trigonometry would be necessary to add the two velocities as vectors.

Areas of Agreement / Disagreement

Participants appear to agree on the need to consider both the center of mass velocity and the relative velocity of points on the wheel. However, there is no consensus on the specific method for calculating the velocity at arbitrary points, as it involves additional trigonometric considerations.

Contextual Notes

The discussion does not resolve the assumptions regarding the application of trigonometry for arbitrary points on the wheel or the specific conditions under which the velocities are calculated.

klandestine
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I know that because of the rolling constraint, V(cm)=R*w [w=omega]. Also, if I want to find the velocity of particle i, i can sum V(cm) and V(i, relative to the center of mass). But how do I determine V(i, rel)? For example, if I am given the speed and radius of a wheel, how fast is a point at the very front edge of the wheel going? I keep trying to use these equations, but I keep coming up with 2wR, which I know is the velocity for the TOP of the wheel.
 
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Realize that the velocity of a particle relative to the cm is a vector whose magnitude is given by [itex]\omega R[/itex] and whose direction is tangent to the wheel. So, if the velocity of the cm is [itex]V \hat{x}[/itex], then the velocity of a point at the front edge relative to the cm is [itex]-V \hat{y}[/itex]. The velocity relative to the ground of that point is [itex]V \hat{x} -V\hat{y}[/itex], giving a speed of [itex]\sqrt{2} V = \sqrt{2} \omega R[/itex].
 
ah-ha!

thank you! so, if i wanted to know the velocity of a point at a more arbitrary location, i would have to use trigonometry, right?
 
Right. You'd have to add the two velocities as vectors, which will involve a bit of trig.
 

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