Name___________________________________ Block_______ Date _______________________
Pulley Lab
Lisa Peck
Purpose: Explore the mechanical advantage provided by different pulley systems
Background: A pulley is a wheel with a groove around the outside edge for a rope or belt to move
around the pulley. Pulleys either change direction of the force or multiply the effort force (MA)
Fixed Pulley: pulley attached to a stationary structure & does not move
changes the direction of the effort force, pulling down is easier with help of gravity
mechanical advantage is 1 (only 1 rope supporting load), doesn’t multiply effort force
Movable Pulley: pulley hung on a rope so it moves up & down with the effort force
does not change the direction of the effort force (same direction as that of the load)
effort distance (din ) is greater than resistance or load distance (dout)
creates a mechanical advantage thus multiplying the effort force
mechanical advantage equals the number of ropes supporting the load
Block and Tackle: a pulley system made up of several fixed and movable pulleys; greater MA
Procedures:
1. Set up the pulley system A using the diagram on the front of the lab.
2. Determine the type of pulley system (single - fixed, single – movable, or “block & tackle”)
3. Determine the Load or Resistance Force: Fout = Fg = mg (what is the mass of the weight?)
4. Attach a spring scale to the end of the string. Pull the string to lift the weight.
Record the effort force: Fin and the direction of the effort force (up or down)
5. Determine the IMA of the pulley system (how many strings are actually supporting the weight?)
6. Determine the AMA of the pulley system.
AMA = Fout / F in
7. Determine the % Efficiency of the pulley system.
% Efficiency = AMA/ IMA
8. Repeat the steps for the other pulley systems (b-e)
Pulley
Type
Load
Fout
Effort
Direction
Effort
Fin
IMA
AMA
% Efficiency
a
b
c
d
e
1. What is the relationship between the number of supporting ropes and the mechanical advantage?
2. When calculating IMA why can you count a section of rope you are pulling up on, but not a section
you are pulling down on?
3. Why would someone want to use a single fixed pulley if there is no MA?
4. As the # of pulleys increase and become more complex, how does the effort force respond?
5. What accounts for the difference between IMA and the AMA in pulleys?