NAME______DATE______

THE PENDULUM LAB

Background Information: Any object that is suspended and is allowed to swing back and forth is called a pendulum. Pendulums swing back and forth due to gravity and their motion is considered regular and constant. Once a pendulum is put in motion it will not change unless some force acts upon it. Pendulums also demonstrate a change from gravitational potential energy (energy due to the position of an object above the earth’s surface) and kinetic energy (the energy of motion). What do you think determines the motion of a pendulum? Find out!

Problem: Which variable will affect how fast a pendulum swings back and forth in a minute, the mass at the end of the string, the length of the string, or the angle of release?

Hypothesis:

Materials: A ring stand with a clamp, 110 centimeters of string or fishing line, 3

hanging weights (10, 50, and 100 grams), a stopwatch or timer, and

a meter stick.

Procedure:

TESTING THE ANGLE OF RELEASE

Set the length of the string to 100 cm

  1. Keep the 10g weight at end of string.
  2. Use the meter stick to measure the angle of release. (see board)
  3. Pull back pendulum 10 cm (5.7 degree angle)
  4. Set your timer to one minute.
  5. Count the # of times it swings back and forth (back and forth=one swing)
  6. Repeat procedure but pull back 20 cm. (11.5 degrees)
  7. Repeat again, but pull back 30 cm (17.5 degrees)
  8. Complete data chart for angle of release.
TESTING THE EFFECT OF MASS
  1. Place the 10-gram weight on the loop at the end of the string.
  2. Loosen the clamp so you can adjust the length of the string. Use the meter stick to make sure it is 100 cm long.
  3. Set your timer to 1 minute.
  4. Pull the pendulum back 10 cm. Keep length at 100 cm.
  5. Press start on timer when you release pendulum.
  6. Count how many times the pendulum swings back and forth in a minute.
  7. Now change the mass variable to a 50-gram weight and repeat.
  8. Change the mass variable to 100 grams and repeat.

TESTING THE EFFECT OF LENGTH

  1. Keep the 10g mass on string. Always pull back 10 cm.
  2. With length of 100 cm count the # of swings per minute.
  3. Change length to 50 cm and repeat.
  4. Change length to 25 cm and repeat.
  5. Fill out data chart.

DATA TABLES

EFFECT OF ANGLE OF RELEASE

MASS = 10 G

LENGTH = 100 CM

ANGLE OF
RELEASE / # OF SWINGS PER MIN.
5.7 DEG. (PULL BACK 10 CM)
11.5 DEG. (PULL BACK 20 CM)
17.5 DEG. (PULL BACK 30 CM)
EFFECT OF MASS

ANGLE = PULL BACK 10 CM EVERY TIME

LENGTH = 100 CM

MASS / # OF SWINGS PER MIN.
10 G
50 G
100 G

EFFECT OF LENGTH OF STRING

ANGLE = PULL BACK 10 CM EVERY TIME

MASS = 10 G

LENGTH OF STRING / # OF SWINGS PER MIN.
100 CM
50 CM
25 CM

PENDULUM LAB QUESTIONS (answer here)

  1. Explain why a pendulum is used in clocks. (Hint: discuss the type of motion it has- see Introduction to Pendulums)
  1. Explain how a pendulum demonstrates the changing of potential energy to kinetic energy. (see diagram). When does a pendulum have the most gravitational potential energy? The most kinetic energy?
  1. When you tested the effect of mass on the rate of a pendulum’s swing did you change the length of string or the angle of release? Explain what you did and why this is important when you test variables.

4. What is the only variable that had an effect on the rate a pendulum swings?

( Explain why or draw a picture to show the effect of length of string.)

5. If you dropped a 50 kg weight and a 100 kg weight which would hit the

ground first? Now explain the results of changing the mass

of the pendulum.

6. Changing the angle of release has an effect on how fast it travels but also the distance it has to travel. Explain how these effects cancel each other out when it comes to the rate of a pendulum’s swing. (Hint: draw a diagram)

7. If your grandfather clock was keeping time too slow, how could you fix it?