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pulley
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mechanical
advantage
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journal
to record data
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fishing line
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book
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scissors
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meterstick
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string
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pulley
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spring
scale
Preparation:
Cut one 30cm length of
string, one 60cm length of string, one 1.5 m length of fishing
line. If groups of students are completing the activity,
each group will need the above materials.
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Students will select a book (mass of about 2 kg to provide substantial
resistance) to lift using the pulley. They will measure the
distance from the floor to the top of a desk. Tie the 60 cm
length of string around the book (see fig. 2 a).
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Have
a student insert the 30cm piece of string through the center
of the pulley and hold the pulley above the desktop by the ends
of the string.
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Another student will tie the 1.5 m of fishing line to the string
around the book, loop the fishing line over and into the groove
on the pulley (the pulley has become fixed as it is held in
place), then attach the spring scale to the other end of the
line.
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A student will pull DOWN on the spring scale to lift the book
from the floor to the desktop. Students will record the force
in newtons used to lift the book and the distance that the book
was lifted. (Work=Force x distance)
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5.
Rearrange the pulley system so that one end of the 1.5 m
fishing line is tied to the desktop, the pulley is tied
to the top of the book, the fishing line is threaded through
the pulley and attached to the spring scale (see figure
2 b). A student will pull UP on the spring scale to lift
the book to the desktop. Record the reading on the scale.
(The pulley has become a single movable pulley in this arrangement)
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When
you use a fixed pulley, what direction did you pull
on the string? In what direction did the book move?
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Compare
the weight of the object with the force used to lift
the object with a fixed pulley.
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Compare
the weight of the object with the force used to lift
it with a movable pulley.
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How
did each pulley arrangement help you do work on the
object?
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