Question

A person riding a merry-go-round passes very close to a person standing on the ground once (event A) and then again (event B). Assume the ground is an inertial frame and that the rider moves at a constant speed. For i, ii, and iii below, answer 1, 2, 3, or 4 and provide an explanation.

i) Which person's watch measures the proper time ΔτΔτ between events A and B?

ii) Which person's watch measures the spacetime interval ΔΔs between those events?

iii) Which person's watch measures the coordinate time ΔΔt between those events in some inertial frame?

1. The rider in the merry-go-round.

2. The person standing on the ground.

3. Both.

4. Neither.

Answer 1

approach 1) as per "newton's law of motion" and "absolute time theory" , Time in itself is moved in all places for all participants at the same rate regardless of the actions of individual objects. thus answer would be both person's watch in all three parts of the question.

approach 2) as per einstein's theory of relativity, time is a relative quantity, Time flows at different rates depending on your speed, acceleration and presence of gravity i.e. faster a person moves, slower his watch becomes

i) answer 4. neither. as both person's watch will show different time though difference might be infinitesimal.

ii) answer 1.  The rider in the merry-go-round. as rider is in motion thus space and time become dependent variable.

iii) answer 2. The person standing on the ground as ground is an inertial frame.