Predictable PendulumsPredictable PendulumsBy Jacob Moyes

As adapted from the Indiana Department of Education

StandardsStandards

Standard 6.1- The Nature of Scince and Technology. ◦ Students design investigations. They use computers and

other technology to collect and analyze data; they explain findings and can relate how they conduct investigations to how the scientific enterprise functions as a whole. Students understand that technology has allowed humans to do many things, yet it cannot always provide solutions to our needs.

6.1.3- Recognize and explain that hypotheses are valuable, even if they turn out not to be true, if they lead to fruitful investigations.◦ Click here to see full activity

DefinitionsDefinitions

Pendulum- an apparatus consisting of an object mounted so that it swings freely under the influence of gravity.

Hyphothesis- a tentative insight into the natural world; a concept that is not yet verified but that if true would explain certain facts or phenomena.

Frequency- the number of times a pendulum swings back and forth per second.

MaterialsMaterials

For the teacher: utility razor or nail, chalk, chalkboard.

For each group of students: paper, pencil, ruler, masking tape, yarn, film canister with a lid, washers or pennies for mass, stopwatch, 2 chairs, copy of Black Line Masters (BLMs) Pendulum Set-Up and Pendulum Observations.

For the class: 2 meters of yarn, clean two-liter soda bottle with a lid, water, stopwatch.

QuestionsQuestions

What is a hypothesis?Are all hypotheses correct?How do scientists determine if a

hypothesis is correct?Can you think of any examples of

pendulums?What part of the pendulum do you think

effects its frequency?

ActivityActivity

Teacher- 1. Prepare a large pendulum by tying a two-meter length of string around the neck of a two-

liter soda bottle. Locate a place to hang it. 2. Punch a hole in the lid of each film canister using the utility razor or nail. 3. Refer to the BLM Pendulum Set-Up and draw a picture of a pendulum on the board. 4. Label the mass, the angle of drop, the length of string, and the frequency. 5. Explain to students that the frequency is the number of times a pendulum swings back and forth per second. 6. Have students suggest two or three hypotheses to test such as: - The mass will affect the frequency of the pendulum. - The length of the string will affect the frequency of the pendulum. - The angle from which the pendulum begins will affect the frequency of the pendulum. 7. Divide students into small groups and pass out the BLM Pendulum Set-Up, the BLM Pendulum Observations, and the materials needed to build

pendulums to each group. 8. Instruct each group to decide on a hypothesis to test. 9. Have students follow the instructions on the BLM Pendulum Set-Up.

Activity (Continued)Activity (Continued)

Students: 1. As a class, discuss the results of each group’s experimentation. 2. Based on their observations, have students pick one variable to test as a class using the large pendulum (such as length of

string). 3. Have students complete three trials (at each length) and check

to ensure that they determined the correct relationship. 4. Ask students which variables affected the frequency of the

pendulum. 5. Ask students if they have a better understanding of pendulums

because they tested multiple hypotheses, even though not all of the hypotheses were correct.

6. Discuss with the students how many discoveries can be made, even when scientists begin their research with faulty hypotheses.

Pendulum ConstructionPendulum Construction

1. Securely tie a length of string between two chairs and pull it taut.2. Measure and cut a piece of yarn. Thread the yarn through the hole in the film canister lid and knot it on the inside so that it will hold the entire canister when the lid is snapped on.3. Place two washers in the canister and snap on the lid. Tie the yarn to the string between the chairs so that it is in the middle.4. Have one person (the counter) sit directly in front of the pendulum between the chairs, have one person release the pendulum, and have one person time.5. It works best to have the counter tell the timer to start the stopwatch when the pendulum has fallen so that it is perpendicular to the ground; the string between the chairs can be used as a reference to determine when a full swing has been completed. 6. Make sure that the person releasing the pendulum drops it from the same height each time.7. The counter should count the number of full swings that occur in five seconds.8. Divide that number by 5 and record the frequency on the BLM Pendulum Observations. Repeat two more times and take the average.9. Repeat steps 4 through 8 with two different masses.10. Repeat steps 4 through 8 three times, keeping the mass the same, but changing the length of string.11. Repeat steps 4 through 8 three times, keeping the mass and length the same but changing the angle from which the pendulum is initially released.

AnswersAnswers

A hypothesis is quite simply an educated guess. Not all hypothesis are correct. For instance, in completing

this experiment I found that my hypothesis that the greatest effect on the pendulum’s frequency would be its mass was untrue. The length of the string was.

Scientists determine if a hypothesis is correct by experimenting. If they can find no evidence that the hypothesis is incorrect, they form a theory.

One example of pendulums are the ones that swing back and forth like a second hand in old grandfather clocks.

Mass, the length of the string or cable supporting it , and its aerodynamic properties all effect the pendulum’s frequency. The angle at which the pendulum is released does not

ReferencesReferences

The Indiana Department of Education http://dc.doe.in.gov

Indiana Standard Resources www.indianastandardsresources.org

What is a Pendulum? www.calacademy.org/products/pendulums/page1.htm