preap the coupled pendulum

7th Grade Pre-AP Unit 2 – Physical Science

Pre-AP The Coupled PendulumTEKS 7.8 A

Teacher

Lesson ObjectivesStudents will

observe and then investigate the motion of a coupled pendulum. develop a reasonable explanation, based on evidence, for the motion of a coupled

pendulum. describe potential and kinetic energy. illustrate the potential and kinetic energy of a coupled pendulum.

Materialsmasking tape meter stickspackaging string scissorspaper clips variety of pendulum bobs (golf balls, metal washers …)chairs stopwatchesbalance

LessonTeacher Demo to begin the lesson.Set up one coupled pendulum system for demonstration by doing the following:

a. Tie a section of packaging string, about 1 meter, between two chairs. This becomes the cross string for the coupled pendulum. Make sure the string is taut, not loose.

b. Make two identical pendulums by adding a bob to a length of packaging string, about 30 centimeters. The demonstration is more dramatic with a relatively heavy bob, like a golf ball. You can tape the pendulum bobs to the end of the strings and bend a paper clip to serve as a hook from which to hang the bobs.

c. Tie each pendulum to the cross string about 30 cm apart. VERY IMPORTANT: Make sure the pendulums are the same length when suspended from the cross string.

d. Try out the coupled pendulum system you have set up. Make sure the system demonstrates alternating motion, as follows:

i. In a coupled pendulum, when you start one pendulum (A) swinging, the other pendulum (B) will start swinging slowly.

ii. Gradually, B will pick up speed and then A will slow down and nearly stop.iii. Soon A will pick up speed again, and B will slow down and nearly stop.iv. The pendulums keep alternating, with one of them moving and then slowing

down and the other picking up speed and then slowing down.

Lesson for students.1. Begin by asking students about their experiences with pendulums by holding up a string

pendulum as a prop and swinging it.a. What do you know about pendulums?b. How did you learn about pendulums?

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2. Show the students the coupled pendulum system you have set up. a. Ask each students to write his or her prediction about what will happen to the motion

of both pendulums when you pull one pendulum back and start it swinging. Ask some to share their ideas about what they think will happen.

b. Demonstrate the coupled pendulum by pulling one pendulum back and letting it go. Ask students to observe the motion of the pendulums and to compare their observations with their predictions.

3. Divide the students into team of three and invite them to explore a coupled pendulum system by using the materials available.

a. Encourage them to change variables, such as string length, string type, wooden dowel instead of a cross string, bob type, bob weight; whatever they would like to explore to learn more about the coupled pendulum.

b. Encourage them to record their observations by writing and/or drawing pictures of what they observe.

c. Encourage them to write down any questions they have as they explore the coupled pendulum system.

4. Have the students write a conclusion of their observations and results. Allow them to use their textbook (pages 190 – 193 and 200 – 201) and other resources to help with the conclusion.

a. The conclusion should include the following vocabulary: coupled pendulum, energy, potential energy, kinetic energy, and energy transformation.

b. In addition, the students should represent their results in an illustration that is labeled with the vocabulary listed in 4.a.

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Pre-AP The Coupled PendulumStudent Page

PurposeTo describe and illustrate the kinetic and potential energy of a coupled pendulum.

Materialsmasking tape meter stickspackaging string scissorspaper clips variety of pendulum bobs (golf balls, metal washers, …)chairs metal washersbalance stopwatches

Procedure1. With your group, set up the coupled pendulum system by doing the following:

a. Tie a section of packaging string, about 1 meter, between two chairs. This becomes the cross string for the coupled pendulum. Make sure the string is taut, not loose.

b. Make two identical pendulums by adding a bob to a length of packaging string, about 30 centimeters. You can tape the pendulum bobs to the end of the strings and bend a paper clip to serve as a hook from which to hang the bobs.

c. Tie each pendulum to the cross string about 30 cm apart. VERY IMPORTANT: Make sure the pendulums are the same length when suspended from the cross string.

d. Try out the coupled pendulum system you have set up. Make sure the system demonstrates alternating motion, as follows:

i. In a coupled pendulum, when you start one pendulum (A) swinging, the other pendulum (B) will start swinging slowly.

ii. Gradually, B will pick up speed and then A will slow down and nearly stop.iii. Soon A will pick up speed again, and B will slow down and nearly stop.iv. The pendulums keep alternating, with one of them moving and then slowing

down and the other picking up speed and then slowing down.

2. Make a record of your observations by writing and drawing pictures of what you observe on the worksheet or in your journal.

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3. Remember, materials such as meter sticks, rulers, and stopwatches are available to collect data. All data should be recorded.

Data (Observations and Drawing)

Date: _______________

Investigation: The Coupled Pendulum

Team Members: _______________________________________________________________________________________________________________

Conclusion:Write a conclusion of your observations and results. Use your textbook (pages 190 – 193 and 200 – 201) and/or other resources to help with the conclusion.

a. The conclusion should include the following vocabulary: coupled pendulum, energy, potential energy, kinetic energy, and energy transformation/conversion.

b. Describe the difference between kinetic energy and potential energy.c. Describe the energy conversions that take place when:

i. the pendulum swings upwardii. the pendulum is at the top of the swing

iii. the pendulum swings downwardd. Label the illustration you made above of the coupled pendulum showing the

pendulum’s kinetic and potential energy.

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preap the coupled pendulum

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