Pulley By: Melissa Hale And Melinda Miller
Simple Machines • A machine is a tool that helps people do more work with greater speed and less effort. • A Simple Machine has few or no moving parts. • A Compound Machine has two or more simple machines working together.
Simple Machines • There are six simple machines: • The lever • Inclined plane • Pulley • Wheel and axle • Wedge • Screw
Simple Machines • Machines do not create energy. • Machines change energy from one form to another. • Example: A blender is a machine that changes electrical energy to mechanical energy. • Can you think of another?
Pulley • Small wheel with groove along its edge, also called a sheave, for holding a rope or cable. • Changes the direction of the force needed to do the work. • Pulleys are usually used in sets designed to reduce the amount of force needed to lift a load. • However, the same amount of work is necessary for the load to reach the same height as it would without the pulleys.
Pulley • The magnitude of the force is reduced, but it must act through a longer distance. • The effort needed to pull a load up is roughly the weight of the load divided by the number of wheels. • The more wheels there are, the less efficient a system is, because of more friction between the rope and the wheels. • Putting several pulleys together really makes the work easier!
Pulley • A pulley is a wheel and axle in its simplest form. • There are two kinds of pulleys: fixed and movable. • A fixed pulley has weight (the load) attached to one end of the rope and effort applied to the other end. • A fixed pulley only changes the direction of the effort.
Pulley • In a movable pulley, the load is attached to the pulley and one end of the rope is fixed to a support. • When the effort is applied to the free end of the rope, the weight is lifted and moved along the rope.
Pulley • Pulleys allow people, animals, and machines to lift heavy objects greater distances because pulling something down is easier than lifting it up. • We can use our own weight to pull the rope downward, and thus pull a load upward.
Pulley • A basic equation for a pulley: In equilibrium, the force F on the pulley axle is equal and opposite to the sum of the tensions in each line leaving the pulley, and these tensions are equal.
Pulley • A simple pulley system – a single movable pulley lifting a unit weight. The tension in each line is half the unit weight, yielding an advantage of 2.
Pulley • Another simple pulley system similar to the previous diagram, but in which the lifting force is redirected downward.
Pulley • A practical compound pulley
Pulley Video provided by: www.unitedstreaming.com
Pulley • Simple Machines Activities
References • Answers Corporation (2007). Pulley. Retrieved April 1, 2007, from http://www.answers.com/topic/pulley-1 • Discovery Education unitedstreaming (2007). Pulley. Retrieved April 1, 2007, from http://www.unitedstreaming.com/search/assetDetail.cfm?guidAssetID=7ABDFA50-927A-47D1-AD00-AF36943B8439
Thank you! The End!