Ok I am confused. As far as I understand it, in SRT two observers will agree on their relative velocity.(adsbygoogle = window.adsbygoogle || []).push({});

How do they calculate it?

[tex]v = \frac{\mathrm{d}x}{\mathrm{d}t}[/tex]

In my rest frame. But in the others rest frame:

[tex]v' = \frac{\mathrm{d}x'}{\mathrm{d}t'}[/tex]

but now for me the length is contracted and the time delated:

[tex]\mathrm{d}t' = \frac{\mathrm{d}t}{\gamma}[/tex]

[tex]\mathrm{d}x' = \gamma \mathrm{d}x[/tex]

[tex]\arrow v' = \gamma^2 \frac{\mathrm{d}x}{ \mathrm{d}t}[/tex]

So we disagree on our differential speed, this must be wrong. What did I miss?

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# SRT two observers will agree on their relative velocity

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