Reconciling Energy Losses on Fast Moving Batteries

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Discussion Overview

The discussion centers around the energy losses experienced by a train moving at relativistic speeds when emitting photons. Participants explore how energy and momentum conservation principles apply in this scenario, particularly in reconciling the energy perceived by observers in different frames of reference.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant describes a scenario where a train moving at half the speed of light emits a photon, resulting in a decrease in energy supply by hf in the train's frame.
  • Another participant suggests that the platform observer can calculate the frequency of the emitted photon in the train's rest frame using the relativistic Doppler formula.
  • A participant reiterates the initial scenario, emphasizing that the emitted photon has momentum and that the train's speed is slightly reduced due to the recoil effect, indicating that energy is drawn from the train's kinetic energy.
  • Another participant agrees with the momentum conservation argument, reiterating that the energy going into the photon affects the train's kinetic energy.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the reconciliation of energy losses and the implications of momentum conservation. The discussion remains unresolved, with no consensus reached on how to fully reconcile the differing energy perspectives of the train and platform observers.

Contextual Notes

The discussion does not address specific assumptions regarding the initial conditions or the exact calculations involved in applying the relativistic Doppler effect. There are also unresolved aspects related to how energy conservation principles apply in this relativistic context.

Joseph14
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Lets say I'm in a train going the 1/2 the speed of light. I have a light source that releases signal photons.

I aim the light source in the direction I'm going and release 1 photon. Now my energy supply for the lamp has decreased by hf. From a person on the platform the frequency is shifted so that the energy in the photon is >hf.

Now when the train returns to platform how can the different energy losses be reconciled, so that both people agree on the energy remaining in the power supply.
 
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Joseph14 said:
Lets say I'm in a train going the 1/2 the speed of light. I have a light source that releases signal photons.

I aim the light source in the direction I'm going and release 1 photon. Now my energy supply for the lamp has decreased by hf. From a person on the platform the frequency is shifted so that the energy in the photon is >hf.

Now when the train returns to platform how can the different energy losses be reconciled, so that both people agree on the energy remaining in the power supply.
The photon also has momentum. From the recoil, by conservation of momentum, the speed of the train is slightly reduced. The extra energy which goes into the photon comes out of the KE of the train.
 
DaleSpam said:
The photon also has momentum. From the recoil, by conservation of momentum, the speed of the train is slightly reduced. The extra energy which goes into the photon comes out of the KE of the train.

Thanks.
 

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