Is Velocity Constant in the Instantaneous Rest Frame?

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Discussion Overview

The discussion revolves around the concept of velocity in the instantaneous rest frame of a rocket. Participants explore the implications of defining velocity as zero in this frame and question how changes in velocity can be discussed when it is stated that v=0.

Discussion Character

  • Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions how velocity can change if it is defined as zero in the instantaneous rest frame.
  • Another participant argues that v=0 at a specific moment does not imply that the rate of change of velocity (dv/dt) is also zero at that moment, suggesting that a broader interval is needed for that conclusion.
  • Some participants propose that there are multiple instantaneous rest frames along the rocket's journey, indicating that the frame changes at each point in time.
  • It is noted that different parts of the rocket (front, back, and in-between) also have distinct instantaneous rest frames.

Areas of Agreement / Disagreement

Participants express differing views on the implications of the instantaneous rest frame, particularly regarding the nature of velocity and its changes. The discussion remains unresolved, with no consensus reached on the interpretation of velocity in this context.

Contextual Notes

The discussion highlights the complexity of defining instantaneous rest frames and their implications for understanding velocity changes. There are assumptions about the continuity of motion and the nature of instantaneous frames that are not fully explored.

luxiaolei
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I have came up some question asking the velocity change of the rocket in its instantaneous rest frame.

And I have been taught that in the instantaneous rest frame, v=0, dgamma/dt =0, gamma = 1. if v is always zero, how come to talk about the change in velocity?

Thanks in advance
 
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v=0 at t=0 doesn't imply dv/dt=0 at t=0. You would need to have v=0 on an interval (-a,a) to get that result, and you don't get that just by using a co-moving inertial frame.
 
luxiaolei, you need to realize there isn't just one instantaneous rest frame, there are lots of them. At each point along the rocket's journey, there is one instantaneous rest frame, but it's a different one at each point.
 
DrGreg said:
luxiaolei, you need to realize there isn't just one instantaneous rest frame, there are lots of them. At each point along the rocket's journey, there is one instantaneous rest frame, but it's a different one at each point.
Not only that, the front, back and every slice in-between the rocket also has a different instantaneous rest frame.
 

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