Question

To whom does an object seem greater in length, an observer moving with the object or an observer moving relative to the object? Which observer measures the object’s proper length?

a) The observer moving with the object; the moving observer measures proper length.

b) The observer moving relative to the object; the moving observer measures proper length.

c) Both observers measure the same length.

d) Neither observer measures proper length.

Answer 1

An object appears greater in length to an observer moving with the object, and this observer measures the proper length, as there is no relative motion causing length contraction.

Step-by-step explanation:

To whom does an object seem greater in length, an observer moving with the object or an observer moving relative to the object? Which observer measures the object's proper length? The answer to this question stems from the principles of special relativity, specifically the phenomenon known as length contraction.

According to these principles, an object appears to be shorter in the direction of motion for an observer who is in relative motion with respect to the object. Conversely, the proper length of an object is measured by an observer moving with the object or, equivalently, by an observer who is at rest relative to the object. This is because length contraction occurs only when there is relative motion between the observer and the object.

Therefore, the observer moving with the object measures the object as it truly is, without the distortions caused by relative motion. This is considered the object's proper length. So, the correct answer to the student's question is a) The observer moving with the object; the moving observer measures proper length.