Sort these motions. For each, say whether it is periodic, and if so, whether it is also an…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Sort these motions. For each, say whether it is periodic, and if so, whether it is also an oscillation.
- The water level at a beach, through several days.
- The Earth turning on its axis.
- A ball dropped on a floor, bouncing lower each time until it stops.
- The needle of a sewing machine running at a steady speed.
- A car on a long straight road at a steady speed.
Need a reminder? The key ideaShow
A periodic motion repeats after a fixed time, the period . An oscillation is a periodic motion to and fro about a mean position. The frequency is , in hertz (Hz).
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, compare your working with the solution.
- Periodic and an oscillation. The level rises and falls about a mean level, with a period of about hours.
- Periodic, not an oscillation. The Earth turns once a day, but it goes round in one direction. It does not move to and fro.
- Neither. The bounces get lower and shorter, so the motion never repeats itself exactly.
- Periodic and an oscillation. The needle goes down and up about a middle position, again and again.
- Neither. The car never comes back.
The rule. Every oscillation is periodic. A periodic motion is an oscillation only if it goes to and fro about a mean position.
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