Reciprocity of Length Contraction

This section introduces the reciprocity of length contraction. Length of a moving object is shorter when measured by a stationary observer; and length of a stationary object is shorter when measured by a moving observer.

Length contraction is reciprocal because moving between two observers is reciprocal. So the following two statements are both true:

The first statement was demonstrated by the thought experiment presented in previous sections. The second statement can be demonstrated by modify that experiment slightly as below:

Reciprocity of length contraction can lead us to some interesting phenomena. For example, we have two trains, a red train and a green train, running side by side in opposite directions. Passengers will experience the following when they are watching the other train passing by:

Length Contraction Reciprocity (
Length Contraction Reciprocity

Last update: 2014.

Table of Contents

 About This Book

 Introduction of Space

 Introducion of Frame of Reference

 Introducion of Time

 Introduction of Speed

 Newton's Laws of Motion

 Introduction of Special Relativity

 Time Dilation in Special Relativity

Length Contraction in Special Relativity

 Length Contraction - Moving Object Is Shorter

 Demonstration of Length Contraction

 Length Contraction Formula and Lorentz Factor

Reciprocity of Length Contraction

 The Relativity of Simultaneity

 Introduction of Spacetime

 Minkowski Spacetime and Diagrams


 PDF Printing Version