Part 10 · Relativity and quantum physics · Card 3 of 11
Length contraction
Objects moving fast are shorter along the direction of motion, by the factor 1/gamma.
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Analogy
A moving ruler looks squashed along its length.
Example
Ship length
gamma = 1.25L = 100 / 1.25L = 80 m
In practice
A 100 m spaceship moving at 0.6c is measured as 80 m long.
Questions people ask
Does the ship really get shorter?
Observers measuring the ship moving at speed find a shorter length along the motion, and that is a real measurement in their frame. People on the ship measure it at normal length. Space and time depend on motion, so length is not one fixed number.
Does length contraction happen sideways?
No. Only the dimension along the direction of motion shrinks. Height and width are unchanged. A fast moving sphere would measure as a flattened disc in the direction of travel. The effect is only noticeable above about ten percent of light speed.