## Pendulum Power

### Tracy Smith

#### Description

Students use a pendulum to discuss the Law of Conservation of Energy and the Second Law of Thermodynamics.

#### Objectives

The student knows examples of natural and man-made systems in which energy is transferred from one form to another.

The student understands how the principle of conservation of energy is applied during an energy transfer.

The student knows that energy conversions are never 100% efficient and that some energy is transformed to heat and is unavailable for further useful work (for example, a food pyramid reflects the energy that is used and lost in each part of a food chain).

The student knows that energy transfer is not efficient.

#### Materials

-Pre and Post test (See associated file)
-Pendulum
-Pendulum handout/ one per student ( See associated file)

Optional Website lesson:
-Television, computer (with Internet access), TVator (used to send computer information to the TV).

Group Activity:
-String/ 1 meter per lab group.
-Small weights / 1 per lab group (washers work well)
-Cellophane Tape/ 1 roll per lab group
-Paper-one sheet per group

#### Preparations

1. Classroom setup suggestion: The pendulum can be hung from the center of the ceiling, so that it swings front to back of the classroom. Student desks can be arranged in rows on either side, facing the pendulum. This way you can instruct in the front of the room and still allow students to see you. (See the design in associated file.)
2. Suggestions for the pendulum:
A rope with a bowling ball tied to one end (Bigger is Better).
Thick twine with a barbell tied to one end.
Yarn with fishing weight tied to one end.
3. Create an overhead of the pendulum picture. (See associated file).
4. Create an overhead from the definition of the Law of Conservation of Energy (See associated file).
5. Create an overhead from the definition of the 2nd Law of Thermodynamics (See associated file).
6. Organize activity materials.

#### Procedures

I. Attention Getter: the swinging pendulum.

III. Discussion: (10 min.)
1.Swing the pendulum
2.Ask what is hanging from the ceiling.
3.Discuss what a pendulum is and give other examples of pendulums.

IV. Objectives: Explain to the students that you will be discussing some of the physics of a pendulum. They will learn the energy conversion that occurs in the pendulum and apply this to everyday life. They will understand that not all conversions are 100% efficient and the reasons for this.

V. Prior Knowledge: (5 min.)
1.Swing the pendulum
2.Discuss the different types of energy involved in a pendulum.
3.If kinetic and potential energy are not mentioned, give clues to the students to bring those answers out.

VI. Lesson: (20-25 min.)
**With optional lesson 30-35 min.
1.Swing the pendulum
2.Give the students the pendulum handout.
3.Ask them where kinetic and potential energy is located on the pendulum.
5.Now, ask them to mark, on the handout, where the maximum kinetic energy and the maximum potential energy is located on the pendulum.
7.Have students pair up and answer the following question on the back of their handouts:
Describe the relationship between the kinetic energy and the potential energy of a swinging pendulum at their highest and lowest points.
8.Discuss their answers. (Students should notice the inverse relationship between the two types of energy and see how one changes into the other.)
9.Display the overhead of the Law of Conservation of Energy.
10.Discuss the law and its relationship to the pendulum. (Energy is not created or destroyed; potential energy converts into kinetic energy, etc.)
**Optional: Use the website, listed in weblinks, to display a moving pendulum on the TV screen. You will be able to manipulate the length of the string and gravitational pull to show the energy changes in the pendulum vs. movement of the pendulum.
11.Homework #1: State and discuss 5 ways that the Law of Conservation of Energy applies to everyday life. An assessment (in associated file) should be presented to students on the overhead, chalkboard, or as a handout.
12.Discuss the next day. (10 min.)

VII. Activity: (30 min.)
“Pendulum Power” Students will construct a pendulum and answer questions referring to the pendulum.
1.Place students into groups of two. If needed, a group of three is fine.
2.Have one student collect materials.
3.Discuss the following procedure steps, before students begin (including the activity assessment – in file).
4.Attach one of the weights to the end of the string.
5.Hang the string from a table, doorway or ceiling.
6.Gently push the weight so that the pendulum begins its motion.
7.Answer on student paper: What do you observe about the pendulum motion?
8.Once all groups are finished, discuss their answers. ( You are looking for them to notice the repetitive motion that has a regular swing pattern)
Explain why the pendulum slows down.
10.Discuss their answers. ( You are looking for students to mention friction and air resistance as factors in the pendulum's deceleration.)
11.This activity will help bring forth the discussion of the Second Law of Thermodynamics.
12.Show the overhead of the Second Law of Thermodynamics definition.
13.Discuss where the wasted heat is on the pendulum and why this machine is not 100% efficient.
14.Discuss other examples of the Second law, such as: moving cars, overhead projectors, eating, etc.
15.Let the pairs of students try to come up with ways to reduce the friction of their pendulum to get the machine as efficient as possible.
16.Discuss ideas. Allow each group to share their ideas.
18.Homework: Research 1 attempt of a perpetual motion machine and why this attempt was not successful OR design a perpetual motion machine and explain why it will be 100% efficient. An assessment (in file) should be presented to the students on the overhead, chalkboard, or as a handout.

**NOTE: An additional day should be used for homework discussion. The post test could also be given this day.

#### Assessments

Summative assessment:
Pre-test
Homework assignment #1
Homework assignment #2
Post-test

Formative assessment:
Pendulum handout with responses to discussion
Activity questions, answers, and responses to discussion

(See Rubric Sheet in attached file.)

#### Extensions

The pendulum and pendulum activity can be utilized for numerous physics concepts. (Examples: conservation of momentum, calculated time vs. actual time, pull of gravity, etc.)