A measurement of the length of an object that is moving relative to the laboratory consists of noting the coordinates of the front and back:
A)at different times according to clocks at rest in the laboratory
B)at the same time according to clocks that move with the object
C)at the same time according to clocks at rest in the laboratory
D)at the same time according to clocks at rest with respect to the fixed stars
E)none of the above

Question

Quizplus · Accepted Answer

The coordinates of the front and back need to be measured at the same time according to clocks at rest in the laboratory to get an accurate measurement of the length of the object. This is because clocks at rest in the laboratory will provide a standard reference frame for measuring the length of the object. Measuring at different times according to clocks at rest in the laboratory would not give an accurate measurement as the object would have moved in that time. Measuring according to clocks that move with the object would result in the measurements being affected by the motion of the object, leading to inaccuracies. Measuring according to clocks at rest with respect to the fixed stars would be impractical as it would require accurate measurements of the position and motion of the stars, and any motion of the laboratory itself would negate the accuracy of the measurements.

A Measurement of the Length of an Object That Is