What+is+a+pulley?+Part+3

By: Olivia, F 2011
 * How does a pulley work? **


 * __[[image:The_pulley.jpg width="445" height="246" align="right" caption="This diagram shows how the pulley is used. The pulley is a simple machine that is combined with a wheel and a pulley. "]]The Pulley__**

The pulley is a simple machine that is used to make things less weight then they really are. They are made like a wheel with a grove in it that can hold a rope; by pulling the rope the object on the other end is being lifted. There are two kinds of pulleys there is a pulley and the movable pulley. A pulley is a wheel used to move power or force by means of a rope or cable is called a pulley. Sometimes you don’t have to have a person pulling the pulley it can just have a counterweight. The more wheels that a pulley has the more friction is caused.


 * __Fixed Pulley__**

The fixed pulley anchored to one spot and it only changes the direction of the object but doesn’t reduce the weight. It only has a one support strand and it only takes one person to hold it. Fixed pulleys work when a force is pulled on the chord. The chord runs through the wheel as the more force is applied. This pulley is only good for objects that don’t weigh that much. With the fixed pulley system the object moves the same distance the rope is pulled in.
 * __The Movable Pulley__**

Movable pulley is a pulley that moves along a rope as you pull it and one end is fastened to a hook then you can start to pull it over. The movable pulley has two support strands which needs more force to pull over because there is more friction between the different wheels. This wheel is fixed to carry

very heavy weight so that this can be used for different kinds of jobs. The rope runs over the upper pulley then through then down and around the second wheel. This allows it to only go half the distance up but takes away a lot of the weight.

__**Block and Tackle**__ Block and tackle is a bunch of different wheels used to raise sustainable loads that has two sets of 3 or more wheels. Each wheel is set free to rotate on the same axle, the upper set is for support, and the lower set is attached to the object. It is a combination of a movable pulley and a fixed pulley. A block and tackle can take away a lot of weight of the object. Keep in mind while you are adding more wheels more friction starts to happen so it is harder to pull.



Citations

Ardley, Neil. //How Things Work.// Pleasantville, Readers Digest, 1995. Print Brain, Marshall. //Marshall Brain’s how Stuff Works.// New York: Hungry Minds, 2001.Print. Macaulay, David. //The Way Things Work.// New York: Houghton Mifflin Company, 1988. Print. //The Block-and-Tackle Pulley//. Prod. Colgren Communications. Colgren Communications, 2001. //Discovery Education//. Web. 15 September 2011. . //Pulleys//. Prod. Cochran. Cochran, 1990. //Discovery Education//. Web. 12 September 2011. //Pulley//. Prod. Colgren Communications. Colgren Communications, 2001. //Discovery Education//. Web. 13 September 2011. []. __GLOSSARY__
 * Counterweight-** something that pulls on a force to move it up or down
 * Friction-** Surface resistance to relative motion, as of a body sliding or rolling
 * Anchored-** to fix or fasten to a surface so that something will stay there