Relativistic Collision Effects on Speed, Mass

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Discussion Overview

The discussion revolves around the theoretical implications of relativistic collisions between two putty balls moving near the speed of light, particularly focusing on the effects of rotation on final speed and mass after the collision. Participants explore concepts related to momentum conservation, energy conversion, and relativistic mass in both rotating and non-rotating scenarios.

Discussion Character

  • Theoretical, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant posits that in a relativistic collision, the final speed (Vf) remains unchanged regardless of whether the collision is head-on or at a slight perpendicular displacement, suggesting that rotation does not affect momentum conservation.
  • This participant also speculates that less energy is converted into mass due to the rotational aspect, leading to a final mass (Mf') that is less than it would be in a non-rotating scenario.
  • Another participant argues that the mass of the system is determined solely by the initial energies of the colliding bodies, asserting that rotation does not influence the final mass.
  • A different participant confirms the initial claim by stating that analyzing the collision from the center of mass frame shows that a spinning mass has more energy and therefore more mass than a non-spinning mass, attributing this energy to the original mass energy of the system.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between rotation and final mass, with some asserting that rotation affects mass and energy, while others maintain that it does not. The discussion remains unresolved regarding the impact of rotation on final mass and speed.

Contextual Notes

Participants acknowledge the theoretical nature of the scenario, noting the assumption that the putty balls can collide and stick together without vaporizing, which may limit the applicability of their arguments.

gsimo1234
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To a moderator: this is a theoretical, concept-based question.

Say two balls of putty, moving relativistically near the speed of light, collide (although i understand this is not possible theoretically and realistically). They collide at a slight perpendicular displacement, instead of head-on, so that in the final state the stuck together system is rotating. Compared to the non-rotating head-on collision, how will this effect the final speed, and how will this effect the Mf' (final mass)? Imagine that you stop the lump from spinning, will its mass be great. less, or equal to Mf'?

Here is what I got out of this situation; Vf remains the same, since rotation does not affect the conservation of momentum. However, less "energy" goes into the mass conversion, so there is less mass. If we stop it from spinning, we do work on the system, adding this rotational energy into the system and the mass willl then be greater to the final mass.

I'm not sure if I'm understanding the theory correct.

P.S. Please don't say "it will vaporize" or "this is not possible"; Let's ASSUME that they stick together relativistically and also rotate, without vaporizing.
 
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If two colliding bodies attach to each other, the system mass is determined with their initial energies solely. It does not matter whether they rotate or not. In the frontal collision it is their atoms/molecules that will rotate/vibrate more.

If you stop the rotation, the mass will become smaller because you take away some energy from the system.
 
by looking at the equations of relativity, your answer actually does make sense; rotate or not, it will have the same final speed and thus same final mass! Thank you so much!

Can anyone confirm this?
 
Yes, you can always analyze the collision from the center of mass frame. In that frame if the final mass is spinning then it will have more energy and therefore more mass than an otherwise identical non-spinning mass. This energy and mass will come from the original mass energy of the system.
 

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