Lesson · Grade 5 · Science
Pulleys: Changing the Direction of a Pull
- Grade 5
- Science
- 1 min 12 s
- British Columbia
- BC5-SC-10
A fixed pulley hanging from a beam lets a hand pull down on a rope to lift a bucket up, and the arrows show the pull is about as big as the load's weight. Adding a movable pulley lets two parts of the rope share the weight, so the pull is about half as big, but the rope has to be pulled twice as far (2 m to lift the load 1 m).
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In one sentence
The question this lesson answers
How can pulling down on a rope lift a heavy load up?
A pulley is a wheel with a rope running over it.
Transcript
What the lesson says
How can pulling down on a rope lift a heavy load up?
A pulley is a wheel with a rope running over it.
This wheel turns, but it stays in one place, so it is called a fixed pulley.
We tie a load, like this bucket, to one end of the rope.
When you pull down on the other end, the load goes up.
The fixed pulley changes the direction of the pull, from down to up.
But you still have to pull about as hard as the weight of the load.
Now hang the load from a movable pulley, which rises with the load.
Now two parts of the rope hold up the load and share its weight.
So you only need to pull with about half the force.
The fixed pulley still lets you pull down to lift the load.
But you have to pull the rope twice as far.
Pull 2 metres of rope, and the load rises just 1 metre.
A fixed pulley changes the direction of a pull, and a movable pulley makes the pull smaller.
Curriculum
Where this fits
- British Columbia, Grade 5
Science, Physics: properties of simple machines and their force effectsBC5-SC-10
Previous: Levers: Fulcrum, Effort and LoadNext: Ramps, Wedges and Screws
The outcomes and strands follow the British Columbia curriculum.
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