=Pulleys= A pulley is simply a collection of one or more wheels over which you loop a rope to make it easier to lift things. Pulleys are usually Force Multipliers - using a simple machine such as a pulley can effectively multiply the force your body produces. However, the rope must be pulled much further because the pulley reduces the distance the object moves. ==How pulleys work== A single-wheel pulley only changes the direction of the force - you pull the rope down to lift the weight up. If you want to lift something with a weight force of 1000N, you have to pull down with a force equivalent to 1000N. If you want to raise the weight 1m into the air, you have to pull the loose end of the rope a total distance of 1m at the other end. [image:http://i.imgur.com/h7H6lsL.png] If you add more wheels, and loop the rope around them, you can reduce the force (effort) you need to lift the weight. If you have two wheels and a rope looped around them, the weight is now effectively supported by two sections of rope instead of just one (ignoring the loose end of the rope you're pulling with). This means you can lift it by pulling with half the force. However, you will need to pull the loose end of the rope twice as far (because both of the sections of rope supporting the weight now have to be shortened). Adding more wheels to the pulley block means that the weight is effectively supported by a larger number of rope lengths. The force required to lift the weight is further reduced, but the loose end has to be pulled much further as each of the rope lengths supporting the weight now have to be shortened to raise it.
Credit: Ben Himme