# Pulleys

Science for the Engineers of the future

### What is a pulley?

If you are studying ESO bilingual Technologies, you must know and understand one of the simplest mechanisms that has been used for ages.

First, take a look at this video to better understand this mechanism and the parts that are used to build a pulley or a block and tackle.

Let’s go Engineers of the future!! The next invention will come from you.  😉

Fixed Pulleys

A pulley is a wheel with a groove that turns on an axis. It is fixed to a solid surface. There is a rope or a chain inside the groove that allows you to lift objects easily by apply a force (F) against a resistance (R).

The pulley is balanced when the force we apply F equals the load R.

F = R

It allows us to lift and lower loads easily and is used in wells, simple cranes and gym equipment.

Movable Pulleys

This is a set of two pulleys, one fixed and another with linear movement. It is balanced when:

F=R/2

With this system, we only need have the force to lift the same weight as with a fixed pulley.

Compound pulley systems

This is a special combination of fixed and movable pulleys.

The more pulleys we have, the more complex the mechanism, but the easier it is to lift the load.
Look at these two compound pulley systems (n is the number of movable pulleys):

Movable and compound pulleys can be used for lifts and cranes

Exercise 1

Listen to the audio below and try to do the exercise about Pulleys. You have 2 tries!! Don’t fail!

## Pulleys listening exercise

Exercise 2

Exercise:  Draw in your notebook the compound pulley system and try to solve this problem: «A block and tackle has two movable pulleys. Calculate the force needed to lift a 1600 N weight and find out the mechanical advantage«

Exercise 3
Exercise:  Copy the exercise in your notebook and try to solve it: «A block and tackle has three movable pulleys. Find out the load we can lift applying a 600N force and work out the mechanical advantage of the machine.«

Watch the Youtube video and answer the following questions in the first 3 minutes of the video. Do it in your notebook.

1.- Write the four simple machines that appear in the first minute.

2.- Complete the following sentences:

“These are simple machines, the basic ___________ blocks of mechanical ______________”

“All simple machines make _____________   _____________”

“Work =  ___________ x distance”

________ Work = _________ Work