The theory of relativity predicts that apparent mass of an object depends on the reference frame. The difference between apparent mass and rest mass is negligible at speeds much less than the speed of light . The value of the relativistic mass for unit rest mass is shown on the graph with a green disk. The radius of the disk is proportional to the value of the relativistic mass and does not mean to indicate that the actual volume of the object changes.
Wolfram Demonstrations Project
Published: March 7 2011