Pendulums

File: Pendulum.pdf

Pendulums Name:_____________________ Section:_________

Glossary

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Cycle: The Smallest complete unit of motion that repeats (1-5 in the diagram)

Period: The amount of time it takes to complete one FULL cycle.

Frequency: The number of cycles per unit of time.

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Displacement: The difference between the initial position and the final position of an object

Amplitude: The maximum displacement the pendulum moves away from resting position.

Before we begin, try swinging the bob back and forth at different lengths to get a feel for its motion before beginning measurements. What, if any, are the effects of changing the string length on the cycle, period, and amplitude?

HINT: Rather than trying to start the Pendulum at exactly at 15 degrees, start the Pendulum at a larger angle, like 20 degrees. Then watch and start measuring the period when the angle has decreased to near 15 degrees.

Our experiment: Which of these things: length, weight, and angle, has the greatest effect on the period of the Pendulum? Write three hypothesis, one about each variable?

Weight :

Length:

Angle:


Part 1. Observing the Effect of Weight.

# of Weights

Time for 10 Cycles (sec)

Period (sec)

0

2

4

6

8

Measure the period by timing 10 complete cycles and dividing the result by ten.

HINT: Start the pendulum swinging then have one student say ‘start’ when the Pendulum reaches one extreme. This same student then counts 1,2,3 … 10 with each count being spoken when the Pendulum returns to the highest point on one side The student who is timing should stop the Timer on the count of ten. Record your data in the table:

Is your Hypothesis supported by this data?

Part 2. Observing the effect of changing the amplitude.

Starting Angle

(degrees)

Time for 10 Cycles (sec)

Period (sec)

10

20

30

Measure the again period by timing 10 complete cycles and dividing the result by ten.

Bring the Pendulum to the starting angle, release it and say ‘start’ when the Pendulum reaches the other side extreme, Counts 1,2,3 up to 10 to the highest point on one that side The student who is timing should stop the Timer on the count of ten. Record your data.

How does this data relate to your initial hypothesis on amplitude?

Part 3. Observing the effect of changing the length of the string.

Vary the length of the string from 10 to 90 centimeters. For this trial the amplitude of the swing should be 20 degrees with 8 weights on the bob. Record your data below, then plot it on the graph.

String Length (cm)

Run Three Trials Each:

Time for 10 Cycles (sec)

Average Time for 10 Cycles (sec)

Period (sec)

10

20

30

40

50

60

70

80

90

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Part 4. Making a Clock.

How many periods will equal one minute?

What string length is needed to make the Pendulum have the desired period?

HINT: Continue using eight weights on the bob, and an amplitude of 15 degrees

Part 5. Test the clock.

How close were you to the right length?

Change the length of the string until you are within 2-3 seconds of one minute.

History

In 1660, the Royal Society proposed that the one-second pendulum be the standard unit of length we know today as the meter. A seconds pendulum is a pendulum whose period is precisely two seconds; one second for a swing in one direction and one second for the return swing.

Ultimately the meter was instead defined, in 1791, as one ten-millionth of the length of the Earth, that is the distance from the Equator to the North Pole.

Why would they choose this instead?

What do you think may change the period of a pendulum from one place to another?