Linear and Circular Motion - Physics Question

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Discussion Overview

The discussion revolves around the dynamics of two colliding objects in free space, specifically focusing on the transfer of linear motion to rotational motion and its implications for net forces and momentum conservation. The scope includes theoretical considerations of motion, energy transfer, and the principles of Newton's laws.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether a collision can result in a net force in the opposite direction due to energy being transferred into spin.
  • Another participant affirms that bodies can have both translational and rotational motion, citing examples like wheels and balls.
  • A participant clarifies that the discussion pertains to action and reaction forces and the potential for movement in free space.
  • Concerns are raised about the misunderstanding of energy transfer, with emphasis on the conservation of momentum during collisions.
  • One participant suggests that if one object spins while the other does not, it could imply a bending of Newton's third law, which is challenged by others who assert that both linear and angular momentum are conserved.
  • Another participant points out that while linear kinetic energy can convert to rotational kinetic energy, there is no conservation law governing this transfer, only for momentum.

Areas of Agreement / Disagreement

Participants express differing views on the implications of energy transfer during collisions, with some asserting that momentum is conserved while others question the interpretation of forces and motion. The discussion remains unresolved regarding the potential for a net force in the opposite direction and the nuances of energy transfer.

Contextual Notes

Participants highlight the importance of distinguishing between force, momentum, and energy, indicating that misunderstandings may arise from treating these concepts as interchangeable. The discussion also reflects varying interpretations of Newton's laws in the context of collisions.

seb7
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Forgive me for questioning basic science, but was wondering..

Two objects of the same mass, traveling towards each other in free space, collide in such a manner as to result in one of them to spin. Since some of the energy in one direction is now lost in the spin, ie. some of the linear force of one of the objects has been tranfered to a spinning motion, would it then be possible to then have a combined net force in the other direction?
 
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What other direction are you talking about?

Yes, it is possible for a body to have both translational and rotational motion. Look at a cars wheel, a baseball, a football, or nearly any ball for that matter.
 
Integral, think you completely misunderstood. I'm talking about the action and opposite reaction, and the possibility of making something move in free space.
 
seb7 said:
Since some of the energy in one direction is now lost in the spin,
Translational KE has been transformed into rotational KE. I don't know what you mean by "in one direction".
would it then be possible to then have a combined net force in the other direction?
I don't understand what you mean. In any case, the net force on the two objects due to their interaction will be zero, as per Newton's 3rd law.
 
seb7 said:
the possibility of making something move in free space.

1. As you have stated in your original post - two bodies collide. That means one of them was already moving, and momentum was conserved in the collision.

2. There is no problem with two bodies in free space starting to move - as long as both energy and momentum are conserved. Imagine two balls connected with compressed (not sure if that's the correct word) spring, hold together by the line. Cut the line - and bodies start to move in the opposite directions. Momentum is conserved, energy is conserved, bodies move in the 'free space'.
 
Both bodies were moving towards each other, so has a combined movement of zero. They collide, object A bounces off in one direction, object B, (because of shape or something) bounces as well, but it is also put into a spin.

Some of the linear motion must have transferred to circular motion. If we can do this without object A spinning, or even just spinning at a slower momentum than object B, wouldn’t we now have some combined movement. ie. a bending of Newton's 3rd law?
 
seb7 said:
Both bodies were moving towards each other, so has a combined movement of zero.
OK. Let's say that the total linear momentum of the two bodies is zero.
They collide, object A bounces off in one direction, object B, (because of shape or something) bounces as well, but it is also put into a spin.
OK. An example might be a ball hitting a stick.

Some of the linear motion must have transferred to circular motion.
Not sure what you mean by this. Both linear and angular momentum are conserved.
If we can do this without object A spinning, or even just spinning at a slower momentum than object B, wouldn’t we now have some combined movement. ie. a bending of Newton's 3rd law?
Nope.
 
Linear kinetic energy can be transferred into rotational kinetic energy, but there is no conservation law for this transfer, only for linear and angular momentum. I think you may be thinking of 'force', 'momentum' and 'energy' as interchangeable, which is incorrect.
 

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