Transcript

Ancient Egypt

Built over 4000 years ago, Egypt's Great Pyramids are 140 metres high.

They are made from very heavy stones.

Many people believe they were built solely by hand.

Others think the Egyptians used a very simple pulley system, using ropes and logs to pull large stones up a ramp.

Pulleys

Pulleys would have made building the pyramids a lot easier.

They reduce the amount of force needed to move heavy objects.

pulleys
reduce force needed to lift objects

They are normally made of wheels and ropes.

A stone with a mass of 50 kilograms requires a force of 500 Newtons to lift it up directly.

Using one rope and one pulley, we would still need to pull with a force of 500 Newtons.

So it would feel just as heavy.

But if you pull the stone with a rope and two wheels, the force for lifting will only be 250 Newtons.

So it will feel like you are lifting just 25 kilograms rather than 50 kilograms.

The pulley gives you a mechanical advantage.

mechanical advantage

But there is a catch.

Even though you pull with less force, you have to pull further, as the rope now has to travel around two wheels rather than just one.

So to move a stone 1 metre, the Egyptians would have needed to pull a rope for 2 metres.

The stones would be pulled on wooden sledges, a lubricant like water would be poured before them to reduce friction.

lubricant

Nobody knows for sure how the pyramids were built.

But the use of pulleys would certainly have helped the Egyptians to create these wonders of the world.

Pulleys reduce the force needed to lift an object.

Video info

Related videos

Cycling to school

Levers