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Yo-yo's:
Experimenting with Pendulums
Goal: Students will how to
apply the scientific method to design features into objects.
Activity: Using the
scientific method, students will determine what affects the time
it takes for a pendulum to swing.
Grade level: 4 - 8
Key Concepts:
- Form and test a hypothesis
- Understand how the scientific
method is used during the design of a product.
Materials:
Directions:
- Hold the yo-yo's string about
a foot from the yo-yo and swing from side to side.
Explain that you know a pendulum can accurately measure
time, but you are not sure what SINGLE thing changes the
period (amount of time for the yo-yo to swing from left
to right, and back again.) State that you have thought of
one thing that might change the period, and that is the
weight at the bottom of the string. Encourage the class
to come up with other possibilities;
- How far back you pull
the yo-yo
- How high up the
string you grasp it. (Your class may think of
others).
- You may want to split the
class into groups depending upon what they think affects
the period.
- Each group must form a
hypothesis stating their "theory." Example;
"We believe that the weight at the end of the string
changes the pendulum's period."
- Stress the following to your
class before they begin experimenting; "To obtain
accurate results, change only one variable at a time.
Otherwise, you will not know what is responsible for the
change."
- Challenge each group to
develop an experiment to prove or disprove their
hypothesis.
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- The "heavy
weight" group could slip two yo-yos into the
loop of string and compare it to a single
weighted yo-yo's period.
- The "pull back
further" group could suspend a yo-yo over a
ruler, then carefully pull the yo-yo back six
inches (15 centimeters), then 18 inches (46
centimeters), and measure whether the period
changes.
- The "grasp the
string" group could measure the period when
the string is grasped 15 inches (38 centimeters)
from the yo-yo, and 30 inches (76 centimeters)
from the yo-yo.
- The period is the time for
one complete back and forth motion. The time to go from
one side to the other side and back to the original
position.
Results:
- Each group should have a
spokesperson describe to the class the group's
hypothesis, describe the experiment they developed to
test that hypothesis, then report whether they proved or
disproved their hypothesis.
- Your class should find that
only one variable affects the pendulum's period - The
length of the string.
Conclusions:
The students have learned to form
a hypothesis, then to develop experiments to prove or disprove
that hypothesis. They should have learned from their
experimentation that the string length is the only variable which
affects the pendulum's period. If this is not the case, the
students inadvertently changed more than one variable at a time.
A bonus project would be to determine how long the string must be
to require exactly one second per swing? Answer - precisely one
meter (about 39 inches).
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