Definition and Theory
A single pulley is used to change the direction of the pull to lift a load. A system of pulleys is used to lift heavy loads by the mechanical advantage of increasing the length of travel of the pull and decreasing the load. The mechanical advantage of a system of pulleys is equal to the number of ropes that support the moveable pulley, less any friction on the pulley. The amount of friction is the difference between the actual load measured and the calculated load.

Variables: P = Load (number of pennies) P(actual) = Actual Load P(calc) = Calculated Load N = Number of Ropes (Mechanical Advantage) P = Pa x N F = Friction F = P(actual) - P(calc.)

Procedure

• There are two experiments designed to show the concept of mechanical advantage using pulleys.
• The first experiment will show the increase in load lifted using pulleys
  • Setup the pulleys to obtain a mechanical advantage of 1, 2, 4, and 6. See the diagram above for pulley arrangement.
  • Apply the loads of 20, 40, and 60 pennies to each setup, (P).
  • Record the amount of pennies required, in the actual load column (Pa), to lift the load in the Data Table 1.
  • Calculate what the amount of pennies should be. The difference is the amount of friction (F).
• The second experiment will show the amount of distance each pulley setup moves the load (P).
  • For each pulley setup (above) measure the lift distance of the load (P) in relationship to the pull distance of the load (Pa). Record the in Data Table 2.
• Answer the questions in the lab.

Laboratory Worksheet