Grade 6 (age 11-12)

Levers & Pulleys

Levers and pulleys move heavy things with a small effort. Pushing far from a lever's fulcrum lifts a load with less force, like scissors and bottle openers. A fixed pulley changes your pull's direction and a movable one halves the force needed. Slide the fulcrum and swap pulleys to watch it change.

Principle of Lever

Fulcrum position30%

💡 What is a Lever?

①A bar and fulcrum used to lift objects

②Fulcrum closer to object → less force

③But you must move a longer distance

④Examples: see-saw, bottle opener, scissors

Types of Pulleys

🔧 Fixed Pulley

①Fixed pulley: attached to ceiling, doesn't move

②Only changes force direction (pull down to lift up)

③Force size is not reduced

④Used in well buckets

Levers & Pulleys in Life

Lever Examples

See-saw / opener / scissors / tongs / nail clipper

Different positions of fulcrum, effort, and load

Pulley Examples

Well bucket (fixed) / Crane (combined) / Elevator (combined)

Lift heavy objects easily

🏗️ Principle of Work

①Tools reduce force but

②You must move more distance to compensate

③Force × distance = work; always equal

④This is the principle of work

Summary

Principle of Work

Force × Distance = Work (always constant)

Tools reduce force but increase distance

🎯 Key Points

①Lever: closer fulcrum → less force

②Fixed pulley: direction only

③Movable pulley: half force (twice distance)

④Combined: direction + force reduction

⑤Principle: Force × Distance is constant

Examples and Unit Test

Example 1

Using one movable pulley to lift an object, what happens to the force needed and the length of rope you must pull?

A movable pulley moves with the object and halves the force needed.

In return, you must pull twice the length of rope.

▸ Force halves; you pull twice the rope

A fixed pulley only changes the direction of force; a movable pulley reduces its size.

Example 2

A tool cuts the lifting force to half. What happens to the work done (force × distance) and the distance moved?

A tool does not change the work done (force × distance); this is the principle of work.

Since the force is halved, the distance doubles so the product stays the same.

▸ Work is the same; distance doubles

Principle of work: a tool reduces force, but the distance increases by the same factor.

Unit-test style

Which statement about levers and pulleys is correct?

①A fixed pulley reduces the size of the force

②A movable pulley halves the force

③A lever lifts with less force when the fulcrum is farther from the object

④Using a tool reduces the work done

⑤Using a pulley does not change the pulling distance

▸ ② A movable pulley halves the force

A movable pulley moves with the object and halves the force (distance doubles).

A fixed pulley only changes direction (①), a lever lifts with less force when the fulcrum is closer to the object (③), the work stays constant (④), and less force means more distance (⑤).

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