Testing pulleys using a test meter
ZIMSEC O Level Combined Science Notes: Experiment:Lifting weights using pulleys
Aim: To use pulleys to lift loads
Materials: 4 single pulleys, string, 1kg mass/a tin filled with sand, spring balance, clamp stand, meter rule
Method
- Set up a fixed pulley as shown above
- Place a 1kg (about 1 Newton) load on one end of the spring
- Use a spring balance/force meter to find the effort required to lift the load
- Set up a single movable pulley
- Determine the force required to lift the 1 kg load
- Set up a block and tackle pulley using a single movable pulley and a fixed pulley as shown above
- Determine the force required to lift the 1 kg load
- Set up two fixed pulleys and two movable pulleys as shown above
- Determine the effort required to lift the movable load
Observation and Results
| Pulley system | Load | Effort | Mechanical Advantage |
|---|---|---|---|
| Single fixed | 10 N | Just over 10 N | Just below 1 |
| Single movable | 10 N | Just over 5 N | Just under 2 |
| One fixed and One Movable | 10 N | Just over 5 N | Just under 2 |
| Two fixed and Two movable | 10 N | Just over 2.5 N | Just under 4 |
- The Mechanical Advantage is below the expected figure due to friction and
- Where applicable the blocks below the fixed pulleys
| Pulley system | Distance moved by load | Distance moved by effort | Velocity Ratio |
|---|---|---|---|
| Single fixed | 15 cm | 15 cm | 1 |
| Single movable | 15 cm | 30 cm | 2 |
| One movable and One fixed | 15 cm | 30 cm | 2 |
| Two fixed and Two movable | 15 cm | 60 cm | 4 |
- In simple terms the M.A and V.R of pulleys is equal to the number of movable pulleys multiplied by two
Conclusion
- Fixed pulleys change the direction of force without impacting on Mechanical Advantage or Velocity Ratio
- They make it convenient to move the load
- Movable pulleys have a Mechanical Advantage and Velocity Ratio of 2
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