Let a rod be at rest in K', lying parallel to the x'-axis. Knowing the value of λ, we can say that:

**(Theorem)** The length of the rod contracts by a factor of √1 – v2 / c2 when viewed from K.

So the distance between the endpoints of the rod is different in K and K', or more generally, the distance that spatially separates two events (i.e. two entities at two given moments, respectively) depends on the inertial frame in which it is measured.

**Note:** length contraction is unnoticeable in our everyday life.