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An object may be regarded to be at rest or in motion depending on the frame of reference chosen to view the object. Because of length contraction it would mean that the same rod may have two different lengths depending upon the state of the observer. Is it true?

Also, Mass of a particle depends on its speed. Does the attraction of the Earth on the particle also depend on the particle's speed?


marked as duplicate by John Rennie special-relativity Jul 3 at 7:30

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