Return to Physics IndexPendulums

Lisa Ingram Frederick Douglass Middle Academy

543 N. Waller

Chicago IL 60644

(312) 534-6176Objective:

To determine the relationship of the frequency of vibration to the pendulum's

length.Materials Needed:

meter sticks (ring stands optional)

tape

string

objects of similar shape but different sizes pendulum bobs

stop watches

calculatorsStrategy:Presentation:

Ask students if they have ever seen a pendulum. Make pictures available of

different types of pendulums.

Ask for two volunteers (a tall one and a short one). Have these two people

stand side by side. Ask half of your class to count the amount of steps that

the tall student takes. Ask the other half to count the amount of steps the

shorter student takes. The two volunteers are to walk together (this is not a

race). Ask students to observe the results and discuss. (They should observe

that the shorter person takes more steps than the taller student in order to

keep up). Discuss how the arm and the leg are pendulums. The leg is attached

and it goes back and forth when taking steps. Discuss another type of pendulum

that you see on a playground, the swing. Discuss how the swing goes back and

forth like a pendulum. (A picture of a swing is optional)Part BPreparation:

Demonstrate to the students how to suspend the pendulum and how to count. If

necessary review the use of the stop watch. Practice timing and counting a

couple of times.Equipment:

The same lengths of string (60cm), pendulum bobs, stop watches, meter sticks.Procedure:

The class is divided into fours' for this activity. There should be a

designated recorder, timer, counter, and swinger. First, the class will be

instructed to take one of the objects and tie a string around it. Second, they

should be given a location to tape down their meter stick. Third, the students

can began to do the following: The recorder has paper and pen and is ready to

write. The timer has the stop watch at zero and is ready to time. The swinger

is holding the pendulum at a suspension and will let the timer know when he/she

will release. The pendulum will be timed for 10 swings. (This means that the

timer hits the start button, when the swinger saids release. The counter will

begin counting 1 when the pendulum comes back toward he/she.) Each group will

do this 3 times. The recorder will write down the times and then average them

with a calculator. A chart will be written on the board for each group to write

down their calculations or timed vibrations.Conclusion:

Students should take note that all of their calculations are very close, if not

the same.Part B: The same groups will repeat the exercise above, however, they

will use different lengths of string (20, 40, 60, 80, 100cm). Each group will

be given their lengths of string to make new pendulums. They will begin timing

10 swings and recording. This data will also be written on the board. (Students

should began to see a difference in the calculations of the other groups

vibrations). The teacher will graph the timed vibrations on the board. The

vibrations on the x-axis and the length of string on the y-axis. As an extra

visual aide, the teacher can tape the actual pendulum of each group on the graph

and discuss.Performance Assessment:

Each group will be given two worksheets to complete. On the first worksheet

will be two questions. They are the following: 1st - Compare your timed

vibration calculations (by looking at the graph on the board) to the other

groups. Write down your observations.

2nd - Compare your timed vibrations again (by looking at the graph on the

board) to the other groups. Write down your observations.

The second sheet will be done individually and it asks the following:

- What affects the vibration of a pendulum?