# Question

You are standing on the Earth and observe a spacecraft speeding by with your professor on board.

(a) If both you and your professor are observing your wristwatch, who is measuring the proper time?

(b) Who measures the proper length of the spacecraft?

(a) If both you and your professor are observing your wristwatch, who is measuring the proper time?

(b) Who measures the proper length of the spacecraft?

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