How fast is a relativistic velocity?

[whydoyouwanttoknow]

How fast do you have to be going before you would be said to have a relativistic velocity?

[jcsd]

Obviously it's subjective, but 0.1c perhaps or even 0.5c?

[selfAdjoint]

The dilations happen at all speeds, even 3 mph. The question is when does the size of the dilations become of interest to you?

[Nenad]

selfAdjoint is right, but I say at 0.1c is where is comes into considerable effect.

[whydoyouwanttoknow]

The dilations happen at all speeds, even 3 mph. The question is when does the size of the dilations become of interest to you?

So your average GPS sat. is going at a relativistic speed because if you didn't take time dilation into account they'd give you the wrong position? But for the rest of us who cares that our car is going 60kph?

[robphy]

Calculate \gamma=\frac{1}{\sqrt{1 - \left(\frac{v}{c}\right) ^2}}.
When your instruments can distinguish \gamma from 1.0 [for example, with a very accurate clock], then you may consider the problem to require relativistic considerations.

[russ_watters]

So your average GPS sat. is going at a relativistic speed because if you didn't take time dilation into account they'd give you the wrong position? But for the rest of us who cares that our car is going 60kph? Yep. So even saying .1C is incomplete: it depends on the situation.