Is Velocity Constant in the Instantaneous Rest Frame?

[luxiaolei]

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

 

[Fredrik]

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.

 

[DrGreg]

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.

 

[Passionflower]

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.