Mechanical Advantage in a Pulley System

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 definition
• formulate their theoretical pattern so that others might understand it
• have their theoretical pattern tested and verified by fellow students
• get practice using a system that they might well use later in life

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 them.
• 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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