--- All motion is measured, described, and predicted relative to some reference frame.
--- Transformation equations connect observations of time, position, or speed made by observers in different reference frames.
--- Two events that are simultaneous in one reference frame may not be simultaneous in another reference frame that is moving relative to the first.
--- All observers in all reference frames measure the same value for the speed of light.
--- Distances measured in a moving frame appear shortened in the direction of motion; this is called length contraction.
--- Time intervals measured in a moving frame appear longer; this is called time dilation.
(c) Doug Davis, 2002; all rights reserved
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