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A pulley is a simple machine that consists of a grooved wheel and a rope or cord. It is used to change the direction of a force and to lift or move objects.
Materials
Materials
Small Pulley
S-Hooks
Thread
Some weight
Strong support
Step 1: Attach Pulley to support
Step 1: Attach Pulley to support
A simple Pulley allows force to be redirected using a thread.
Single pulley does not act as a simple machine as it only redirects force.
Step 2: Add a Moving Pulley
Step 2: Add a Moving Pulley
A moving Pulley is added to the thread as shown.
The End of thread is attached to the anchorage point.
The weight is attached to the movable pulley.
Pulling the thread will lift the weight
Step 3: Pulley on pulley
Step 3: Pulley on pulley
More Pulleys can be added to as shown.
Each pulley has one end of the thread attached to anchorage point and other end of the thread is attached to a moving pulley.
Compound Pulleys
Compound Pulleys
Compound Pulleys add more than one pully in single set up
Compounding of pulleys effectively reduce number of anchorage points required in the setup.
Compound Pulley in action
Compound Pulley in action
Thread is attached from the bottom hook as shown.
Thread passes through each pulley sequentially and exits from the topmost pulley.
Weight is attached to the hook at the bottom.
Pulling on thread lifts the weight.
Explanation:
Lifting a 10 kg Weight with 2 Movable Pulleys
When multiple pulleys are used in a system—especially movable pulleys—they reduce the amount of force needed to lift a weight by distributing the load.
Let’s say you want to lift a 10 kg weight using a pulley system with 2 movable pulleys.
The total weight (force due to gravity) is about 100 newtons (since 10 kg × 9.8 m/s² ≈ 98 N).
In a system with 2 movable pulleys, the weight is shared by 4 rope segments (each movable pulley effectively doubles the rope segments supporting the load).
This means each segment supports about 25 N of the weight.
As a result, you only need to apply 25 newtons of force to lift the 10 kg load—four times less than lifting it directly!
This demonstrates the mechanical advantage of pulleys: by increasing the number of pulleys, we reduce the effort needed, even though we may have to pull more rope length.
Watch the video Detailed explanation of Simple Machines:
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