PULLEY LAB
PHYSICS 212 WORKSHEET
Pulleys are simple machines—i.e., they allow you to change the direction and/or the magnitude
of the force you exert on an object. For each question below, consider the pulley systems shown
on the next page. After you have predicted a result for each question, you will be directed on page 3
to build each of the four systems to see how well you have predicted. At that time you may change
your answers.
1.
Which of the pulley systems shown on the next page will change the direction of the applied
force?
2.
Predict by how much each pulley system will reduce the applied force needed to move the
mass. Also explain how you reasoned your predictions. (Hint: How many strings are
actually holding up each mass?)
System #
Amount of force reduction (stated as a fraction)
1
2
3
4
44
2
1
pull
mass
pull
mass
3
4
pull
pull
mass
mass
45
3. Now, one at a time, build each of the four pulley systems and test the predictions you made on
the first page. For each system of pulleys, slowly raise the mass by 5 cm, and calculate the
work you do. In each case, also calculate the work done by the pulley system. How do they
compare? Discus your results below the table.
system #
force you distance you
applied to pulled*
the string
amount of
work you
did
force exerted
on the mass
the distance
the mass
moved
1
5.0 cm.
2
5.0 cm.
3
5.0 cm.
4
5.0cm.
amount of
work done
on the mass
*Be sure you record the actual distance your hand and fingers move. This might be different
from the change in amount of string between your hand and the nearest pulley.
Discussion of results:
46