# Testing Variables Students will manipulate variables of a pendulum; draw conclusions from experimentation with pendulums Why should you test only one variable.

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Testing Variables Students will manipulate variables of a pendulum; draw conclusions from experimentation with pendulums Why should you test only one variable at a time?

Testing Variables of a Pendulum A pendulum is an old, but accurate timekeeping device. It works because of two natural phenomena – gravity and inertia – that are important in the study of Earth Science. Gravity makes all objects fall toward Earth’s surface. Inertia makes matter remain at rest or in motion unless acted upon by an external force. In the following activity, you will test some variables that might affect the swing of a pendulum

What You’ll Investigate How do the length of a pendulum, the attached mass, and the angle of the release of the mass affect the swing of a pendulum?

Procedure Bend the paper clip into and S shape and tie it to one end of the string. Hang one washer from the paper clip. Measure 10 cm of string from the washer and hold the string at that distance with one hand. Use your other hand to pull back end of the pendulum so it is parallel with the ground and let go. Count the number of complete swings (back and forth) the pendulum makes in 1 minute, record it on your chart. Repeat. Repeat changing the string length as you go.

Procedure Using 50 cm of string, attach another washer pull the end of the pendulum level with the floor and release. Count the number of complete swings it makes in 1 minute, and record it on your table 2 chart. Repeat with 3, 4, and 5 washers.

Procedure Using only one washer, and 50 cm of string, count the number of complete swings in 1 minute using the varying angle measures. Record your data in the 3 rd chart.

Conclude and Apply 1.When you tested the effect of the angle of the drop of the pendulum on the swings per minute, which variables did you keep constant? 2.Infer which of the variables you tested affects the swing of a pendulum. 3.Suppose you have a pendulum clock that indicates and earlier time than it really is. (This means it has too few swings per minute) What could you do to the clock to make it keep better time? If you have time: graph your data from your tables, and compare it with other groups data.

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