Lorentz factor for moving inertial reference frames is(adsbygoogle = window.adsbygoogle || []).push({});

λ = [itex]\frac{1}{\sqrt{1 - \frac{v^{2}}{c^{2}}}}[/itex],

where v is the relative velocity between the frames. But in my textbook (I'm only just learning relativity), it says the Lorentz factor for a particle is

λ_{p}= [itex]\frac{1}{\sqrt{1 - \frac{u^{2}}{c^{2}}}}[/itex],

where u is the velocity of the particle...but what's the difference between these two expressions?

The textbook introduces λ_{p}during the derivation of relativistic momentum, so I'm fine with where it came from, but then without explanation the book starts using it for time dilation Δt = λ_{p}Δ[itex]\tau[/itex]. Little confused so would love it if someone could clear this up for me.

Thanks in advance!

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# What's the difference between Lorentz factor for frames and for particles?

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