You stand on a corner as a friend drives past in an automobile.You both note the time interval required for the car to travel one block,and you both measure the distance traveled.The proper time interval is measured by _____,and the proper distance is measured by _____.
A)you; you
B)you; your friend
C)your friend; you
D)your friend; your friend
E)your friend; both of you

Question

Quizplus · Accepted Answer

According to the concept of time dilation in special relativity, the proper time interval is measured by the observer who is stationary relative to the event. In this case, the person standing on the corner is stationary while the car is moving, so they would measure the proper time interval. On the other hand, the proper distance is measured by the observer who is at rest relative to the distance being measured. Since the distance between the two points (i.e. one block) is fixed and stationary, both observers would measure the same proper distance. Therefore, the friend driving the car would not measure the proper time interval or the proper distance. The only choice that reflects this is C: your friend measures the time interval, and you measure the distance.

You Stand on a Corner as a Friend Drives Past