Mechanical Advantage in a Pulley System
Copyright 1999 by James P. Riser
Purpose - This lab activity was designed to present
my students with the opportunity to:
- manipulate lab equipment
- work with only one obvious variable
- search for an experimentally repeatable pattern
- design a data chart to reflect the needs of the experiment
- identify a pattern based upon actual measurements and a simple
- formulate their theoretical pattern so that others might
- have their theoretical pattern tested and verified by fellow
- get practice using a system that they might well use later
The equipment used is merely two pulleys(as shown),
a 1000g hooked mass,
some string, and appropriate spring balances.
Teams - I prefer to have students work in teams of four
students on this activity. This allows for better dialog within
the team and makes holding the equipment easier as the pulleys
are threaded with the string.
Additional info -
- Many students will have trouble threading the pulleys - team
members will need to hold pulleys in position.
- The measurements will be rather straight forward - use the
appropriate ranged spring balances.
- Students will probably have trouble at first seeing the relationship
between the number of "sustaining ropes" and the Mechanical
Advantage - a little frustration can be good for them.
- If students might be having too difficult a time determining
a pattern, you might suggest that they round off their measurements
and calculations. This could make things much more apparent to
- Give them enough time.
- Accept only neat data charts and well written comments, conclusions,
etc. My students are required to produce these with a computer.
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