Return to Physics IndexOscillations

Foreman, Dorothy Joplin School

874-6161

Objectives:(1) To construct various types of pendulums. (2) To prove that the mass of the bob and the range of the oscillation (5^{o}-15^{o}) do not affect the period of a simple pendulum.

(3) To prove that the length of the swing arm does affect the period

of a simple pendulum.

(4) To diagram each activity dealing with oscillations.

(5) To graph length versus frequency.

(6) To observe energy transfers in coupled pendulums of the same

length.

(7) To demonstrate knowledge of the formula: T=2pi times the square

root of L/G.

(8) To use a simple pendulum to measure the gravitational constant G.

(9) To observe the Pulfrich Pendulum and to make predictions regarding

the illusions it causes the eyes to see.

(10) To use a pendulum bob to make Lissajous figures.Apparatus needed:

protractors, graph paper, meter sticks, metric rulers, stop watches,

various sizes of dowel rods, string, washers, metal balls, scissors,

empty 2 liter plastic bottle, overhead projector, sand, balance, ring

stands, metal supporting rods, c-clamps, scientific calculators, tape,

polarizing film, eye hooks, wood glue, drill, saw, sand paper, screws,

nails, wooden blocks, safety glasses.Recommended Strategy:Procedure for Pulfrich Pendulum:Set a simple pendulum swinging in a plane. Have students observe its back and forth movement. Have students cover one eye with polarizing film and observe the movement of the pendulum with both eyes open. The pendulum appears to swing in a circle either clockwise or counter clockwise, depending upon which eye is covered. Make predictions regarding the illusions.Procedures for testing variables:length, mass, and amplitude: Students will work in groups. Set up work stations around the room. Give each group washers of equal sizes, stop watches, protractors, c-clamps, rods, tape, string, and graph paper.Testing variable length:(1) attach one washer to each swing arm, (2) release each bob at 10 degrees amplitude, (3) vary lengths of swing arms: 25cm, 50cm, 75cm, 100cm, 125cm, 150cm, (4) one student will count the number of cycles in one minute. (One student will either time one minute, or will time ten cycles) Do three trials. Average data. Calculate the period for each pendulum. Record all data in data table. Graph length versus time. Using formula, find G for each pendulum tested.Testing variable mass:(1) keep all swing arms the same length, (2) keep all amplitudes 10 degrees, (3) vary number of washers added to swing arms, (4) record results, (5) reach conclusion about the affect of mass on the period of the simple pendulum. Testing variable amplitude: (1) keep all swing arms the same length, (2) add one washer to each swing arm, (3) Vary the amplitude from 5 degrees to 15 degrees, (4) record results, (5) Reach conclusion about the affect of amplitude on the period of a simple pendulum.Procedure for coupled pendulums:Suspend two pendulums of same length from the same thin dowel rod (string could be used in place of the dowel rod); suspend this rod from a supporting rod. Start with the pendulums at rest. Start one pendulum swinging. The first pendulum begins to lose amplitude while the second pendulum starts to swing faster and faster. At one point both pendulums swing together, with the same period. Finally, the first pendulum comes to rest, and all the energy is in the second pendulum. (1) Predict what will happen next, (2) Observe this phenomenon by means of an overhead projector, (3) What caused both pendulums to finally come to rest?Procedure for making Lissajous figures:(1) fill 1/4 of plastic bob with white sand, (2) punch small hole into the center of bottom of the bob and cover the hole with tape, (3) attach large eye hook to top of bob, (4) carefully tape the bob together, (5) attach a short string to the eye hook, (6) attach to the slip knot at the top of string, another string, which when slid through the knot forms a triangle 7/10's the length of the entire system; attach each end of the string triangle to a supporting rod, (7) adjust rod so that the bob hangs 3cm from the black paper covered table, (8) uncover hole, (9) set bob in motion, (10) observe the Lissajous figures made out of sand. (Experiment with colored inks, sugar, etc.)