lab: Salt Clay

GRADE SCHOOL LAB
INVESTIGATING THE PENDULUM

INTRODUCTION:

Galileo studied the pendulum, and discovered the relationships of length, weight, and time of its swing. In this activity you will investigate the effect of weight and length on the time of a pendulum swing. This investigation is easier with two people working together.

MATERIALS NEEDED:

String
3 identical large washers
Masking tape
Scissors
Pencil
Ruler
Meter stick
Heavy book
Stop watch or watch with a second hand
Table

NOTE: measure everything in metric units. We use metric units in science, because different units are multiples of 10. For example:
1 centimeter = 10 millimeters
1 meter = 100 centimeters

PROCEDURE:

Investigating the effect of weight on time of swing.

construct a pendulum as shown in the drawing, using one washer. You choose the length of the pendulum that is appropriate for your table height. It is important to measure the length with the weight pulling down on the string, because string stretches, and you want to know the actual length. Record your pendulum length on your DATA TABLE. A pencil mark on the table leg will help to make all tests the same. Also, make a pencil mark on the table to indicate the ruler placement, so you can keep everything the same except weight.

One person holds the pendulum level with the marked point on the tab leg, while the other keeps time. When the timer says now, release the pendulum ( do not push or pull back, simply release it from level to the marked point ). The pendulum operator then counts the number of swings ( one swing is a complete movement from level to the marked point and back ). The time keeper will say stop, at the end of 10 seconds. Record on your DATA TABLE the number of swings.

Now repeat the procedure with a pendulum constructed using two washers. Make sure everything is identical, except that the weight is twice as much as the first pendulum. Again count the number of swings in 10 seconds and record on your DATA TABLE. Remember, keep everything identical to the first try except weight.

Now repeat the procedure one more time, using a pendulum constructed from three washers. Again be careful to keep everything the same, except weight. Count the number of swings in 10 seconds, as before, and record in your data table.

ANALYZING YOUR DATA:

Look at your data for the 3 pendulum tries. Knowing that everything was identical, except for the weight, what conclusion can you make about the effect of weight on the time of swing for a pendulum? Write your answer in the appropriate place on the DATA TABLE.

PROCEDURE:

Investigating the effect of pendulum length on time of swing.

construct a pendulum as shown in the drawing, using one washer. You choose the length of the pendulum that is appropriate for your table height. Again, it is important to measure the length with the weight pulling down on the string, because string stretches, and you want to know the actual length. Record your pendulum length on your DATA TABLE as length for trial 1. It will be easier to hold the meter stick up and choose a distance for the swing. Remember, this time, we want everything the same except the pendulum length.

One person holds the pendulum level with the marked point of release, while the other keeps time. When the timer says now, release the pendulum ( do not push or pull back, simply release it ). The pendulum operator then counts the number of swings. The time keeper will say stop, at the end of 10 seconds. Record on your DATA TABLE the number of swings for trial 1.

Now repeat the procedure with the pendulum ¹ / ₂ the length of the pendulum in trial 1. Record your pendulum length on your DATA TABLE as length for trial 2. Make sure everything is identical, except that the length is one-half as much as the first pendulum. Again count the number of swings in 10 seconds and record on your DATA TABLE. Remember, keep everything identical to the first try except the length.

Now repeat the procedure one more time, with the pendulum ¹ / ₄ the length of the pendulum in trial 1. Record your pendulum length on your DATA TABLE as length for trial 3. Again be careful to keep everything the same, except length. Count the number of swings in 10 seconds, as before, and record in your data table.

ANALYZING YOUR DATA:

Look at your data for the 3 pendulum tries. Knowing that everything was identical, except for the length of the three pendulums, what conclusion can you make about the effect of pendulum length on the time of swing for a pendulum? Write your answer in the appropriate place on the DATA TABLE.

DATA TABLE:

Investigating the effect of weight on time of swing.

Length of your pendulum for this study. = __________

Number of swings for 10 seconds:

For 1 washer: _______

For 2 washers: _______

For 3 washers: _______

What conclusion can you make about the effect of weight on the time of swing for a pendulum?

________________________________________________________________

Investigating the effect of pendulum length on time of swing.

Trial	Pendulum Length	Number of Swings
Data for 10 second time trial.
1
2
3

What conclusion can you make about the effect of pendulum length on the time of swing for a pendulum?

________________________________________________________________

DISCUSSION:

For the effect of weight on time of swing.

The number of swings in 10 seconds, is the same for all three pendulum weights. This is because gravity pulling on the pendulum weight causes it to fall when released. As the drawing shows, the pendulum speed increases as the pendulum approaches the vertical position and then slows as it moves upward until it stops. This is then repeated over and over. The force of gravity pulls on all objects the same, regardless of weight, so changing only the weight of the pendulum does not change the speed of the swing. Therefore the time of the swing remains the same.

Investigating the effect of pendulum length on time of swing.

The number of swings doubled for trial 3, as compared to trial 1. Galileo discovered in his experimenting, that the time of one swing of a pendulum decreased by one-half, if the length was one-fourth the original length.

FURTHER INVESTIGATIONS:

Repeat the pendulum length experiment, but this time use about 10 different lengths. remember to keep all other aspects identical for each trial. Graph the number of swings for 10 seconds vs. the pendulum length. Do you think you will get a straight line, or a curved line?

You tested two aspects of a pendulum. Devise your own experiment to test another aspect of the pendulum. Again, remember to keep all other aspects the same, so only the effect of the one you are investigating will be effecting your data.

Go to the library and research Galileo. You may find other things to investigate from this early scientist's work.

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