Motion and forces
Measuring time
Say how old clocks kept time, find a pendulum's time period from a count of oscillations, and convert between the second, the minute and the hour.
A clock, whether it is a bowl with a hole in it or an atomic clock, does one trick: it finds something that repeats at a steady rate and counts the repeats. A shadow crawling round a stone dial. Sand running out of a bulb. A candle burning down past its marks. A crystal shivering millions of times a second. Different processes, one idea.
The pendulum, and what it gave us
A simple pendulum is a bob hung from a rigid support by a long thread. At rest it hangs at its mean position; pulled aside and let go, it swings out to one extreme position, across to the other, and back. That whole round trip is one oscillation, and the time it takes is the time period. Galileo found the surprising part by timing a swinging lamp against his own pulse: for a pendulum of a given length, that time comes out the same swing after swing.
Have a play
The parts of a simple pendulum, and where the bob reaches at one extreme.
Tap any part of the picture.
Worked example
A pendulum is set swinging and timed. Ten oscillations take 16 seconds. What is its time period?
Notice why ten were timed rather than one. A single swing is over too fast to time by hand, and any slip in starting or stopping the watch is the whole measurement.
Shared out over ten swings, that same slip is a tenth as much per swing. This is why the activity says ten and not one.
Try it together
Work down from hours to seconds, one step at a time.
Answer each step with a bare number.
1.A film runs for 3 hours. How many minutes is that?
Have a go
Have a go on your own. A pendulum completes 10 oscillations in 30 seconds. What is its time period, in seconds? Answer with a number.
Ready to practise?
Eight questions on what you have just read. Nothing is timed, and you can play as many times as you like.