Calculators | Texas Instruments - Science | Pendulums

Pendulums

By David Proctor,

Katanning SHS

If you use or quote from the following programs, please acknowledge the author above.

• Pendulum I
• Pendulum II
• Pendulum III

Pendulum I

In this activity you are to obtain two descriptions of how a pendulum moves.

Description 1:   You are to write a brief description of the motion of a pendulum. As a young scientist, you are to base your description on measurements that you have made.

Description 2:   You will use the graphics calculator and motion detector to obtain their description of the motion of the pendulum.

Construction:   Use string, fishing line or light rope to construct a simple pendulum that has a length of between 1.5 m and 2.0 m. The bob of your pendulum needs to be large enough to be easily detected by the motion detector. Swing your pendulum and make sure that it swings freely and without spinning.

Measurement:   Make some preliminary observations of your pendulum swinging. You need to observe your pendulum along the line that it is swinging. Discuss with your partners what measurements you could make to accurately describe the motion of the pendulum during 5 swings and what might be the best way to record your measurements and observations. Once you have come to an agreement, swing your pendulum, make and record the appropriate measurements.

Motion Detector:   Repeat your experiment, but this time use the motion detector and TI 83 calculator to measure and record the motion of the pendulum.

• Use the PHYSCI program to produce a displacement graph.
• When giving the instructions on the calculator:
  1. Set up probes first. The motion detector will be on the second screen of probes - select (7 more probes) to go this screen and then select the motion probe (3).
  2. Collect data next (2) and select time graph (2).
  3. Initially, enter 0.05 seconds as the time between samples, and enter 200 as the number of samples.
  4. Use the time set up (1) and start the pendulum and motion detector. Make sure that the pendulum is the only item moving near the detector. When the following message appears on the screen time in L1 sonic in L4,L5,L6 push ENTER and then select (1)   DISTANCE.
     The calculator will then draw a distance versus time graph of the pendulum's motion.
  5. If the graph is not satisfactory push ENTER and select (4)   RETURN and (2)   REPEAT.

Questions:

1. What measurements has the detector made?
2. How has the calculator represented the motion? Could you have represented your information in a similar fashion? (Perhaps you did!)
3. What does the calculator's graph tell you about the motion of the pendulum? (ie copy the graph and explain what the different levels on the graph are saying about the pendulum.
4. Use the cursor keys to move along the graph. What do X and Y represent? Use the cursor keys to find the difference in the X values and the difference between the Y values between two successive peaks. Explain what information these two sets of differences provide about the motion of the pendulum.
5. Repeat the experiment but examine what happens to the information stored on the calculator if you alter the time between samples and the number of samples taken. Is there a minimum time that the detector can be made to operate for? Is there a maximum number of measurements that the calculator can store?

Pendulum II

Design an experiment to determine what factors affect the time it takes for the pendulum to complete one swing (this is the period of the pendulum).

Write your experiment report as an article to be included in the school newsletter to inform parents about the properties of pendulums.

Before starting the experiment you might need to consider the following:

1. List factors that you think might change how long it takes for a pendulum to complete one swing. Discuss and compare your list with other people.
2. The factors that affect the period of the pendulum are called variables. Select one variable to examine, how can you keep all of the other variables constant while changing just the selected one?
3. How can you improve the reliability of your experiment? ie How could you be more confident that the one time you did the experiment was a true reflection of what happens every time the pendulum is swung.
4. Try the same idea but change which variable you examine and which variables you control.

Pendulum III

• Design a pendulum that has a period of 1 second. Use the CBL to show that it has period of 1 second.
• The greater the time period that a pendulum swings for, the shorter its swing. Why?
• It is not possible to make a simple pendulum always swing along the one line - as time goes on it always starts to swing in a different line. Try to find out why.