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TE Activity: Swing in Time

Students examine the motion of pendulums and come to understand that the longer the string of the pendulum, the fewer the number of swings in a given time interval. They see that changing the weight on the pendulum does not have an effect on the period. They also observe that changing the angle of release of the pendulum has negligible effect upon the period.

Engineers use the motion concepts learned from pendulums in many applications, including timekeeping, earthquake detection, satellite orbits and energy dissipation. Control engineers incorporate pendulums into vibration isolation systems for manufacturing and industrial equipment, and controlling walking robots and rocket thrusters. Inverted pendulum systems monitor dam performance and structural behavior by detecting angular movement. Anti-sway software builds upon pendulum concepts to provide more safe and efficient operation of construction cranes, yard cranes, telescoping boom cranes and shipboard cranes.

Pre-Req Knowledge
Learning Objectives
Materials
Introduction/Motivation
Vocabulary
Procedure
Attachments
Safety Issues
Troubleshooting Tips
Assessment
Extensions
Activity Scaling

Grade Level: 6 (5-7)	Group Size: 3
Time Required: 45 minutes	Activity Dependency : None
Expendable Cost Per Group : US$ 1
Keywords: mechanics, Galileo, force, pendulum, angular momentum, gravity, oscillation, period, weight

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Colorado Science
- Standard 1: Students understand the processes of scientific investigation and design, conduct, communicate about, and evaluate such investigations. (Grades 0 - 12) [1995]
- Standard 6: Students understand that science involves a particular way of knowing and understand common connections among scientific disciplines. (Grades 0 - 12) [1995]
- 2.1 Students know that matter has characteristic properties, which are related to its composition and structure. (Grades 0 - 12) [1995]

Waves in water go up and down, cars bounce up and down when they hit a bump, and people go back and forth when they are playing on a swing. Can you think of other things that have a regular back and forth motion? Items that move back and forth regularly move in similar ways. If scientists and engineers can understand one kind of back and forth motion, such as a swing, then they can apply that understanding to other items that move in a back and forth motion.

In this activity, you will examine the motion of a pendulum. If you have ever played on a swing set, you are already familiar with some of the ways that a pendulum can move. In this lab, you will examine specific factors that might affect the way a pendulum swings. You will time a pendulum swinging back and forth, and see what factors make it speed up and what conditions make it slow down.

The motion of a pendulum was first mathematically described by a man named Galileo Galilei in the late 1500s. Galileo also investigated how things fall, how planets move, and many other scientific phenomena. Many of his discoveries grew out of his observations of how a pendulum swings. Just think — maybe you can figure out how something works by understanding pendulums!

Pendulums were not only used in the 1500s, though. Engineers use the motion of pendulums today. In fact, some of the most advanced building designs incorporate large pendulums to dissipate the energy if the building is shaken by an earthquake. Engineers use pendulums in robots and in clocks. Can you think of useful ways to use a pendulum?

Pendulum :	A string with a weight at one end suspended from a fixed support, so that it swings freely back and forth, under the influence of gravity.
Bob:	The swinging weight at the end of a pendulum.
Gravity:	The force that attracts bodies toward the center of the Earth.
Period:	The amount of time it takes the bob of a pendulum to return to its initial position.
Oscillation:	The back and forth swinging motion of the bob of a pendulum. One oscillation is complete when the bob returns to its starting position.

Before the Activity

Cut string pieces to 110 cm.
Attach either the 1 oz. or the 2 oz. weight to all pendulums.
Label fishing weights 1 oz. and 2 oz.
Copy enough Swing in Time Worksheets for each group.

With the Students

Introduce the activity: Ask the students if they know what a pendulum is. Ask them if they know how pendulums are used. Tell them they will learn more about pendulums and their movements in this activity. See Lesson for more background information and motivation.
Pass out worksheets. Instruct students to follow along with the activity.
Working in groups of three, have students measure and mark their string at 10 cm intervals, starting measurement at the middle of the weight and marking up to 100 cm.
Have the students tape the pendulum to their desk at the 10 cm mark.
Pull weight back at a 45-degree angle for consistency in the swing.
Predict and test: First have the students predict the number of times the pendulum will swing back to its original starting point (a swing or oscillation) during a 30 second timing, for the pendulum length and weight being tested, and record this in the worksheet table. Next, have one student time the swing for 30 seconds and two other students count the actual number of complete swings (oscillations), and record this in the worksheet table.
Repeat the "predict and test" process, taping at the next 10 cm increment (20 cm). Repeat again, up to a 50cm length.
Have students create a bar graph with the number of swings (oscillations) on the vertical axis and the pendulum length on the horizontal axis. Students should observe a pattern.
Repeat the procedure using the second weight. Ask students to observe any differences between the two weights (there should be no difference).
The bar graph should look similar to the example. (Note: The weight has a negligible effect on the number of swings, but due to experimental error there may be a slight discrepancy.)

a. Bar graph of the Number of Swings Versus Length of Pendulum. The x-axis shows the length of string in cm. The y-axis shows the number of swings in 30 seconds. There are two series (for 2 pendulum weights) indicated by different bar colors.

Students should be able to make a prediction for the results at the 60 cm to100 cm lengths, following the pattern.
Have students continue to record their predictions, test and record their results on the worksheet.
Review and discuss worksheet answers with the entire class.

Swing in Time Worksheet

Pre-Activity Assessment

Discussion Question: Solicit, integrate and summarize student responses.

Ask students if they know what a pendulum is. Brainstorm examples of pendulums (Possible answers: Playground swings, rope or tire swing from a tree, a grandfather clock, a circus trapeze, balancing mechanisms for some robots, etc.)

Activity Embedded Assessment

Worksheet: Have the students record their lab observations and measurements, and follow along with the activity using the Swing in Time Worksheet.

Pairs Check: After student groups finish working on worksheets, have them compare answers with another completed group, giving all students time to finish the worksheet.

Post-Activity Assessment

Worksheet Discussion: Review and discuss worksheet answers with the entire class. Use the answers to gauge students' mastery of the subject.

Sand Pendulum: Make a cone-shaped cup and fill it with sand or salt. Swing the cone like a pendulum, letting the sand pour out from a hole in the bottom of the cone. Observe the pattern it makes.

Experiment with two or more pendulums at one time: Swing the pendulums in the same direction, in the opposite directions, two one-way and one another, criss-cross, etc.

Predict the amount of time it will take the pendulum to come to a complete stop.

Ask students to find a string length that makes the pendulum swing exactly 60 times per minute. How would this be useful? (Answer: A pendulum could be used as a clock if each swing took one second.)

Integrated Teaching and Learning Program, College of Engineering, University of Colorado at Boulder Sabre Duren, Ben Heavner, Malinda Schaefer Zarske, Denise Carlson © 2004 by Regents of the University of Colorado.
The contents of this digital library curriculum were developed under a grant from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and National Science Foundation GK-12 grant no. 0226322. However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government.

Last Modified: April 27, 2006