EntityQ3153623· pop 6· linked from 156 articlesproper lengthSign in to savelength of an object in the object's rest frameConnectionsspacetimeEntitytimeEntityInternational Standard Book NumberEntitytheory of relativityEntityspeed of light in vacuumEntityclassical mechanicsEntityspecial relativityEntitygeneral relativityEntitydigital object identifierEntitycoordinate systemEntitythree-dimensional spaceEntitybibcodeEntitytensorEntityQ118398Entityinertial frame of referenceEntitylength contractionEntityorthogonalityEntityQ22908627EntityLorentz factorEntityline integralEntityCategoriesTheory of relativity