Proper length

Definition

Proper length is the length of an object measured by an observer who is at rest relative to the object. It represents the maximum length of the object and is not affected by relative motion.

5 Must Know Facts For Your Next Test

1. Proper length is denoted as $L_0$ in equations.
2. It remains constant regardless of the relative velocity between observers.
3. Proper length is measured in the frame of reference where the object is stationary.
4. Length contraction only affects lengths measured in frames moving relative to the object, not proper length.
5. In special relativity, proper length helps calculate contracted length using the Lorentz factor.

Review Questions

• What does proper length represent in terms of an object's measurement?
• How does proper length differ from contracted length when observed from different frames of reference?
• Why does proper length remain unaffected by relative motion?

Related terms

Length Contraction:

A phenomenon in special relativity where an object's measured length decreases when it moves relative to an observer.

Lorentz Factor:

A factor $\gamma = \frac{1}{\sqrt{1 - \frac{v^2}{c^2}}}$ used in relativity equations to account for time dilation and length contraction.

Relativity:

The theory proposed by Albert Einstein that describes how measurements of space and time vary for observers in different states of motion.