Measuring time at all depends on the fact that:
AClocks must be electric
BMotion must be uniform
CDistances must be known
DSomething must change
Answer & Solution
Correct answer: D. Something must change
1. Time is registered by counting repetitions of some process.
2. It is impossible to know that time has passed unless something changes.
3. A pendulum can measure time by counting its swings.
4. Connecting that pendulum to a clock mechanism registers the count on a dial.
5. Any repeatable change will do, which is why so many different clocks exist.
_Source: OpenStax College Physics for AP(R) Courses 2e (CC BY 4.0), Ch 2 'Kinematics', sections 2.1-2.8_
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