Simple and Compound Pulleys

This demonstration shows the difference between type 1 (fixed), type 2 (movable), and type 3 (compound) pulleys. Using low-friction pulleys, string, and measured masses, students observe how pulleys can reduce the input force required to lift weights and compare the forces using a force sensor.

1. Gather materials: 6 low-friction pulleys, 3 strings of different lengths, 2 table clamps, 6 right-angle clamps, 3 × 1 kg masses, 3 × 100–200 g masses, laptop, force sensor, and 850 Universal Interface (see first link).
2. Secure clamps to a stable table to hold pulley supports.
3. Set up a type 1 (fixed) pulley by attaching a pulley to the support, tying one end of the string to a 1 kg mass, and passing the string over the pulley. Pull down on the free end or attach the force sensor to measure required force.
4. Set up a type 2 (movable) pulley by attaching the pulley to the load and securing one end of the string to the support. Pull on the free end or connect it to the force sensor. Compare the force reading to the load’s weight.
5. Set up a type 3 (compound) pulley (block and tackle) by combining fixed and movable pulleys. Attach multiple pulleys to both the load and the support. Thread the rope through alternating pulleys, then connect the free end to the force sensor.
6. Record and compare force measurements from all three setups.
7. Discuss the relationship between the number of supporting rope segments and the mechanical advantage.

Single and compound pulleys review - lifting our principal - Homemade Science with Bruce Yeany:

Experiment with pulleys! - STEM Quick Wins:

📄 1-2-3-PULLEYS! - Idaho State University: https://www.isu.edu/physics/outreach/physics-class-demos/mechanics/1-2-3-pulleys/

• Demonstrate with different load masses (lighter or heavier weights) to show proportional force changes.
• Use colored ropes for each pulley type to clearly distinguish fixed, movable, and compound setups.

• Ensure clamps and pulley supports are tightly secured to the table before applying force.
• Keep feet and hands clear of falling weights; do not stand directly under suspended masses.
• Use strong, thick string to avoid breakage under load.
• Check pulleys for smooth operation to prevent sudden jerks.
• Lift weights slowly and steadily; avoid rapid pulling.

• How did the measured force compare between the fixed, movable, and compound pulley setups? (Fixed: equal to load weight; Movable: about half the load; Compound: divided further depending on rope segments.)
• What trade-off occurs when force decreases in a pulley system? (You must pull a longer length of rope.)
• How do engineers use compound pulleys in real-world systems? (Examples: cranes, elevators, sailboats, gym equipment.)
• Why is a low-friction pulley important in this demonstration? (To reduce losses so the mechanical advantage can be observed more clearly.)