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š¬ Pull down to lift up
To raise a flag we pull a rope downward and the flag goes up. A pulley turns an awkward upward pull into an easy downward one.
How does a pulley help, and what is its mechanical advantage?
- A pulley is a grooved wheel that guides a rope. A fixed pulley does not reduce the force needed — it only changes the direction (pulling down is more convenient than lifting up).
- Since effort and load are equal in magnitude, the mechanical advantage of a fixed pulley is 1 .
- A movable pulley (or a system of pulleys) can give a mechanical advantage greater than 1 , lifting heavy loads with smaller effort.
Fixed pulley
Movable pulley (system)
Pulley is fixed to a support.
The load is attached to a movable pulley.
Only changes the direction of the effort.
Reduces the effort needed to lift the load.
Mechanical advantage = 1.
Mechanical advantage greater than 1.
Important Definitions
- Pulley — a wheel with a groove that guides a rope; a fixed pulley changes only the direction of the effort (mechanical advantage 1).
- Movable pulley — a pulley attached to the load; a movable pulley system can give a mechanical advantage greater than 1.
š¹ Ready to Go Beyond
- In a movable pulley system the load hangs from the movable pulley, one rope end is fixed, and the other is free for the effort. Such systems lift heavy objects with small effort and are used in elevators and cranes .
