This is a level 4 measurement activity from the Figure it Out series.
A PDF of the student activity is included.
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use pendulums to explore time and length
FIO, Level 3-4, Measurement, Pondering Pendulums, page 13
stopwatch, ruler
classmate
Investigation One
One way to make a pendulum that is easily adjusted is to use a fishing line with a sinker on the end. Hang the line over a plank that is 1 centimetre thick, and then use a spring peg to clip the line to the plank. The students can easily adjust the length, and the pendulum swings more truly than if the line is held by hand.
Investigation will show that the shorter the length of the string, the faster the pendulum completes a full swing and the longer it is, the slower the swing. Note that the length of the arc that the pendulum swings does not affect the time of the swing. Only the length of the string affects the time. This is how some pendulum clocks are adjusted for accuracy. The weight is moved slightly up or down the length of the arm.
Investigation Two
The result of the investigation in question 1 should confirm that as long as the string length is unaltered, the time taken for each full swing will always stay the same, even though the speed of the pendulum slows down. Discuss the reason for this. The students may be able to see intuitively that as the pendulum slows, the swing distance shortens, so the time for each swing stays the same.
A good website that can be used for the investigation in question 2 is www.howstuffworks.com
Answers to Activity
Investigation One
Investigation will show that the shorter the length of the string, the faster the pendulum completes a full swing and the longer it is, the slower the swing.
Investigation Two
1. As long as the string length is unaltered, the time taken for each full swing will always stay the same even though the speed of the pendulum slows down.
2. Research activity