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Year 7 & 8 TOC

Levers & Pulleys


LO: Investigating a simple machine such as a lever or a pulley system 

A pulley is a rotating wheel with a grooved circumference. These grooves provide grip and friction for the rope.

They am to change the direction and size of an applied force.

Have you ever had a static shock? When you drag your feet on the ground you build up a positive charge and when you go close to someone the charge jumps to the other object.

Types of pulleys

The most simplest pulley system only involved one pulley. This system changes the direction of applied force, however the weight you pull doesn’t change. So if the container weighs 100 g, you need to apply 100 g of force or 1 Newton to lift it. 

The reason a single pulley still makes things easier, is because the person lifting can use their entire body weight to lift the object.   

The more pulleys we use the easier the load becomes to lift. If we use 2 pulley, than the load is halved. Meaning the mechanical advantage is 2. So, in order to lift a 100 kg crate, we only need to apply 50 kg of force, or 500 N, with a network of 2 pulleys.

If we add 4 pulleys, we only need to apply ¼ of the load. Meaning, if we try lifting a 100 kg container, we only need to only apply 25 kg of force to lift it, if there are 4 pulleys. 

The mechanical advantage is 4

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