Video Transcript
Which of the following physical quantities can be measured by an hourglass, a pendulum clock, and a digital stopwatch? Is it (A) mass, (B) length, or (C) time?
Let’s start by looking at the digital stopwatch. We are likely already familiar with what a stopwatch is, or at least the watch part of a stopwatch, and how it’s used to measure time. Stopwatches typically have two buttons that allow you to start and stop measuring time. After pressing the start button, a stopwatch will continuously count upwards until it is stopped. Stopwatches are handy for measuring minutes, seconds, and fractions of seconds, which are all units of time.
Similarly, pendulum clocks are clocks which also measure in units of time, with the smaller hand measuring hours and the larger hand measuring minutes. But it is not always necessary to have to quantify the units of time in hours, minutes, or seconds, such as in the case of an hourglass.
Hourglasses measure time through the falling of sand from the top of the hourglass through the neck down to the bottom. The time that this takes varies between each individual hourglass, with smaller hourglasses typically measuring in minutes and larger hourglasses typically measuring in hours. But hourglasses are unlabeled. What matters most is that they measure the passage of time at all, rather than measuring a specific quantity.
So then in their own ways, an hourglass, pendulum clock, and digital stopwatch all measure time. The correct answer is (C) time.
