Mechanical Advantage in a Pulley System

Purpose - In this lab activity you will have 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 your own theoretical pattern so that others might understand it
• have your theoretical pattern tested and verified by fellow students
• get practice using a system that you 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 - Teams of four students on this activity seems to work well. This allows for better dialog within the team and makes holding the equipment easier as the pulleys are threaded with the string.

Terms that you will need to know:

• Effort - the force applied to a machine
• Resistance - the force that the machine overcomes
• Mechanical Advantage - the number of times a machine multiplies the force applied to a machine
• Mechanical Advantage may be expressed as the Resistance divided by the Effort

Your task is to arrange the two pulleys into the systems illustrated.

• The mass (Resistance) should remain constant at 1000g.
• You will need to record the Effort for each system - use the spring balance to get this.
• Design your own data chart to organize and record your measurements.
• Calculate the Mechanical Advantage for each system - record this on your chart.
• Carefully study the systems and the calculated Mechanical Advantage.
• As a team, identify a pattern for predicting Mechanical Advantage.
• Come up with an experimentally repeatable pattern theory for predicting the Mechanical Advantage of a system without actually measuring the effort.
• Test out your theory to see if it is valid.
• Ask another team to test your theory.
• Record the results of these tests and write up your conclusions regarding your team's theoretical pattern .
• Explain how friction might affect your pattern. Explain where you might use a pulley system in daily living.
• Turn in your data chart with all of your findings and explanations. Put all team member's names on it!