Pulleys

What is a pulley? A pulley is a grooved wheel that performs a similar function to a gear. Pulleys do not have teeth like gears. A rope, belt or cable fits into the groove of a pulley, which enables the pulley to rotate.

Like gears, a pulley system has the ability to change or transfer rotary motion. Pulleys make work easier. “Refer to diagram one”

Even though the person still has to exert an effort of 500N to lift the box of bricks, the action of pulling downwards is far easier than standing on the roof and trying to pull upwards. Remember, the input is the persons effort, the process is the pulley system and the output is the box of bricks moving upwards.

Compound Pulleys Pulleys can increase mechanical advantage or make the work easier. The greater the value of mechanical advantage above 1, the easier the work is. You can work out the mechanical advantage in pulleys using the following formula:

Mechanical Advantage Mechanical Advantage = Load/ Effort In the diagram the person has to use an effort of 500N to lift the bricks. The mechanical advantage is: Mechanical Advantage = Load/Effort Mechanical Advantage = 500N/500N Mechanical Advantage = 1

Mechanical Advantage = Load/Effort Mechanical Advantage = 500N/500N Mechanical Advantage = 1

This means that the person lifting the bricks has not really gained much advantage by using this pulley system, although pulling downwards makes the work easier. Look at the next diagram to see how adding more pulleys to the pulley system can increase the mechanical advantage.

Here the person is using a compound pulley system to lift the bricks Here the person is using a compound pulley system to lift the bricks. A compound pulley system has two or more pulleys in the pulley system. By using two pulleys, the person has increased the amount of times the rope supports the load. This makes it easier to lift the load, but it also means that the rope has to be moved further.

Effort = Load/The number of ropes supporting the load To work out the amount of effort required to lift the load, use the following formula: Effort = Load/The number of ropes supporting the load

Effort = Load/The number of ropes supporting the load Effort = 500N/2 Effort = 250N

Now that you know the effort required, you can work out the mechanical advantage. Mechanical advantage = Load /Effort Mechanical advantage = 500N/250N Mechanical advantage = 2

This means that the mechanical advantage has increased making the work twice as easy, but it also means that the rope has to be moved twice as far.

Test What is a pulley? In what way does a pulley system help make work easier? What is the formula used to work out mechanical advantage in a pulley system?

A person sets up a pulley system to lift a set of ten wooden poles off the ground. The wooden poles have a mass of 25kg each. The person uses a force of 500N to lift the poles. Calculate the mechanical advantage of this pulley system. (Hint – Remember to convert all units into SI units) If you know how many supporting ropes there are in a pulley system, you can calculate the effort required in that pulley system to lift a load. What formula do you need to use?

Calculate the effort required to lift this load. A person sets up a pulley system to lift a car engine. The pulley system has four supporting ropes. The engine has a mass of 800kg. Calculate the effort required to lift this load. Calculate the mechanical advantage that this pulley system has.

A Grooved wheel and axle that works with chain,cable or rope. It is Changing the direction of the force that makes it easier to do the work. MA = Load/ Effort