Pendulum Investigation: Measuring Time
GRCC Physics
Somewhere in the room you should find materials for creating and studying a simple
pendulum. For our purposes a “simple pendulum” is just a weight that is free to swing
from a piece of string, which is tied at the other end to a support that won’t move. Divide
into groups, and within your group begin creating and investigating your pendulum. For
centuries the pendulum was the standard device for measuring time. The amount of time
it takes for the pendulum to swing from one extreme position, to the other extreme
position, and back again is called the period of the pendulum.
1. Make your pendulum: Make your pendulum so that it can stand on the table
where your team is working. (It should not be so big that it is difficult to move it
if we have to take it down and put it up again elsewhere.) You shouldn’t need
more than a stand, a horizontal support that you can hang the string from, a string,
and a weight that you can suspend from the string. You can work without a stand
if you can swing your pendulum from a table or other high object.
Hints:
¾ Make sure that the weight can swing without toppling the stand! (To do
this you may need to change your design.)
¾ Also, you should think about ways to change your investigations as you
learn more about your pendulum. If you make the parts of your pendulum
too permanent, you won’t be able to modify them for an experiment.
Start a brief report about your pendulum. Include the names of all of the
people in your group and a brief description of the design of your pendulum.
Label this as section 1 of your report.
2. Investigate your pendulum: Together with your group partners, come up with
some questions that you can imagine asking about the period of your pendulum.
What sorts of things might influence the period? How could you go about looking
for answers to these questions? Are some of them more easily answered than
others? What might changes in your design do to the behavior of your pendulum
and how could you study the changes?
Include some of these ideas in your brief report. What ideas do you and your
teammates have about the pendulum? Label this as section 2 of your report.
3. Choose a question for investigation: Choose one of the many things that might
influence the period of the pendulum to investigate. Discuss with your teammates
how you will investigate the changes in this variable (your independent variable).
Discuss how you will control potentially bothersome extraneous variables.
Record your question and your independent and controlled variables in your
report (as well as the way you intend to control the moderator variables).
4. Choose one hypothesis: Together with your group partners, create a hypothesis
about your pendulum. The hypothesis should be a statement about your question.
It must be a statement that can be proven wrong (“I hate pendulums” is not a
testable hypothesis). It should also include some idea of why someone might
think your hypothesis is true. It should test the connection between the behavior
of the pendulum and some sort of model. It is often suggested that students word
their hypothesis in the form “If… then… because…”. Can you see why?
Write down the exact wording of your hypothesis. The wording should make it
clear to you exactly how you would know at the end of your experiment
whether you needed a new hypothesis. Label this as section 4 of your report.
5. Plan your investigation: (In case you hadn’t figured it out yet, record this part
in section 5 of your report.) Look for some equipment you could use to carry out
your investigations and conduct tests. Start with the investigations that you think
should be fairly simple and work on harder ones if you get done with these. You
should be able to find equipment in the room, but you can always ask your
instructor if you think you need something that you do not see.
¾ Before you begin your investigations:
i. Discuss a plan for the investigation with your group members and
make sure they agree on a course of action. (You do not have to
follow this course exactly, but you should have a plan.)
ii. PREDICT! Just for fun, go through your group and ask each team
member what they expect to happen when you do your tests! It is
always much more interesting to do an experiment after you have
thought about what behavior you expect to see.
¾ Record your plan and your predications in your report!
6. Investigate. NOW begin your investigations! Record your results in your report.
Do they agree with your expectations? If not, try and decide whether you did
something wrong in your investigation or whether your expectations were wrong.
¾ Take enough data to create a clear picture of your results.
i. You will probably collect more data than you can easily read in
one sentence. Record your data in a format that is easy to read.
ii. You will need to present data. Come up with a way to present your
data that makes your results as clear as possible.
¾ Record these results in your report.
7. Conclude. What can you conclude from your results? Discuss this with your
partners and draw some reasonable conclusions.
¾ Remember: It is not important or even desirable for your hypothesis to
be correct! Nobel prizes have been awarded to people for experiments
that proved reasonable hypotheses to be wrong!
¾ Record your conclusions in your report.