Length contraction (A-level only) Flashcards – AQA A-level Physics (7408)

What is length contraction?

The reduction in an object's measured length along its direction of motion relative to an observer.

What is an object's proper length?

Its length measured in its own rest frame.

What is the length-contraction formula for an object with proper length $l_0$ moving at speed $v$?

$l = l_0\sqrt{1-\frac{v^2}{c^2}}$ Here, $c$ is the speed of light in a vacuum.

How does length contraction change as an object's speed approaches the speed of light?

The contraction becomes greater.

When measuring a moving object's length, when must its endpoints be measured?

Simultaneously in the observer's frame.

How does motion affect an object's measured lengths perpendicular to its direction of motion?

They are unchanged.