Final answer:
In physics, events marking the end of a period can be indicated by audible signals like bells, buzzers, or whistles, or by visual signals like a flag waving, depending on the context.
Step-by-step explanation:
Within physics, an event that marks the end of a period could be signaled by an observable change or a specific sensory cue. The examples provided, such as a bell ringing, a buzzer sounding, a whistle blowing, or a flag waving, can all serve as indicators. The choice between these options depends on the context of the situation. For instance, in laboratory experiments, precise timing might be necessary, and therefore an audible signal like a buzzer or a whistle is preferred. On the other hand, flag waving might be less precise and could be used in events where visual signals are appropriate, such as the end of a racing event.