Angular and linear velocity question

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Discussion Overview

The discussion revolves around the behavior of a long, rigid object, specifically a plank, when it is rotated and then released. Participants explore the implications of angular and linear velocities, particularly in relation to the object's center of mass and the varying linear speeds of different points on the object.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions how a long plank, when released after being spun, behaves given that different points on the plank have different linear velocities.
  • Another participant asserts that the center of mass of the plank will continue in a straight line, while the various pieces will have different initial velocities that correspond to their rotation about the center of mass.
  • A third participant explains that despite the different linear velocities, all parts of the plank share a common angular velocity about the center of mass, and upon release, the pieces will rotate around the center of mass while the center of mass itself follows a straight-line path, assuming no gravitational forces act on it.
  • A later reply suggests observing hammer throw competitions as a practical demonstration of the discussed principles.

Areas of Agreement / Disagreement

Participants generally agree on the behavior of the center of mass and the concept of angular versus linear velocity, but the initial question about the specific dynamics of a long object remains open for further exploration.

Contextual Notes

There is an implicit assumption that the plank behaves as a rigid body, and the discussion does not address potential effects of gravity or air resistance in detail.

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I have a question, let’s say I’m holding a long piece of wood such as. 1’ x 6’ plank and I’m rotating it in a circle by spinning around with my hands extended, I suddenly let go, what happens to the velocity of the wood since every point on the wood that is a different distance from the center of rotation is traveling at a different linear speed. I’m assuming the wood will try to spin around it’s center of mass but how would that work when the wood is let go of has all different velocities . Was just curious because when reading about physics of centripetal force it says the object will move about in a straight line but I’m assuming that’s for small objects likes balls and such, nothing is ever discussed when you have an object that is long and is spinning and let go of. Maybe I should try spinning a board but since I don’t have a safe place to do this I figured I would ask.
 
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The object's center of mass will continue in a straight line. The various pieces start with various velocities relative to the center of mass that amount to a rotation about that center.
 
The wood is a rigid body. Although pieces on it have different linear velocities, they have a common angular velocity about the center of mass at all times. When you let go, these pieces will rotate about the CM while the CM will describe projectile motion in general or will move in a straight line if gravity is not acting on it.
Physics is awesome said:
Was just curious because when reading about physics of centripetal force it says the object will move about in a straight line but I’m assuming that’s for small objects likes balls and such, ...
You are assuming correctly.
 
Check out videos from hammer throw competitions. They're doing the experiment for you.
 
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