A rod has a proper length of 100 m. An observer moving relative to the rod at 0.80c measures its length. What length does that observer measure?

1. Length contraction gives L = L0 divided by gamma. 2. With v = 0.80c, gamma equals 1 divided by the square root of (1 minus 0.80 squared), which is about 1.667. 3. Divide the proper length by gamma: L = 100 divided by 1.667. 4. Dividing gives L of about 60 m. 5. 100 m is the proper length itself, measured at rest with the rod, not what the moving observer sees. 6. 48 m and 80 m do not match this division. 7. So 60 m is correct, since it is the length the moving observer measures, contracted from the 100 m proper length. _Source: OpenStax Physics (CC BY 4.0), Ch 10 "Special Relativity", section 10.2 Consequences of Special Relativity_