Does Zero Linear Momentum Always Mean Zero Kinetic Energy?

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Discussion Overview

The discussion centers on the relationship between linear momentum and kinetic energy in a system of particles. Participants explore whether zero linear momentum necessarily implies zero kinetic energy, and they seek examples to clarify this relationship. The conversation also touches on the implications for angular momentum.

Discussion Character

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

Main Points Raised

  • One participant states that if the kinetic energy of a system of particles is zero, then the linear momentum must also be zero, but the reverse is not necessarily true.
  • Another participant provides an example of two particles with equal mass moving in opposite directions, resulting in zero momentum while maintaining non-zero kinetic energy.
  • A request is made for an example where kinetic energy is zero but momentum is non-zero.
  • Further clarification is sought regarding the calculation of kinetic energy and whether any terms can be negative, alongside a consideration of the system as a whole.
  • One participant expresses understanding after receiving input from others.

Areas of Agreement / Disagreement

Participants generally agree on the initial claim regarding the relationship between kinetic energy and linear momentum, but there is no consensus on examples that illustrate the conditions where kinetic energy is zero and momentum is non-zero. The discussion remains unresolved regarding the latter scenario.

Contextual Notes

Participants express uncertainty about the implications of kinetic energy being zero and the conditions under which momentum can still be non-zero. There are unresolved mathematical considerations regarding the definitions and calculations of kinetic energy.

Who May Find This Useful

This discussion may be of interest to students and educators in physics, particularly those exploring concepts of momentum and kinetic energy in systems of particles.

AdityaDev
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"if kinetic energy of system of particles is zero, then linear momentum of that system of particles is zero but the reverse is not true. That is if linear momentum of a system of particles is zero, then the kinetic energy may not be zero"

This is what I got from my text. Can you provide me with some examples because I am a bit confused. Can you provide some explanation?
Is this true for angular momentum?
 
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Consider two particles with mass m, one with velocity +v and one with velocity -v.
 
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Vanadium 50 said:
Consider two particles with mass m, one with velocity +v and one with velocity -v.
So momentum is zero and kinetic E is not zero. Can you give an example for kinetic energy zero and momentum non zero?
 
AdityaDev said:
So momentum is zero and kinetic E is not zero. Can you give an example for kinetic energy zero and momentum non zero?
KE = sum of 1/2 mv2. Can any of those terms be negative?
Or, imagine covering the whole system with a curtain or box and treating it as one object of total mass M and velocity V.
P=MV, while KE= 1/2MV2+ KE(within system, relative to the center of mass)
If KE = 0, what does that imply? Assume masses are never negative.
 
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