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Pulley. 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.

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Presentation on theme: "Pulley. 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."— Presentation transcript:

1 Pulley

2 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.

3 Simple Machines  There are six simple machines:  The lever  Inclined plane  Pulley  Wheel and axle  Wedge  Screw

4 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?

5 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.

6 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!

7 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.

8 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.

9 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.

10 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.

11 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.

12 Pulley  Another simple pulley system similar to the previous diagram, but in which the lifting force is redirected downward.

13 Pulley  A practical compound pulley

14 Pulley Video provided by: www.unitedstreaming.com

15 Pulley  Simple Machines Activities Simple Machines Activities Simple Machines Activities

16 References  Answers Corporation (2007). Pulley. Retrieved April 1, 2007, from http://www.answers.com/topic/pulley-1 http://www.answers.com/topic/pulley-1  Discovery Education unitedstreaming (2007). Pulley. Retrieved April 1, 2007, from http://www.unitedstreaming.com/search/as setDetail.cfm?guidAssetID=7ABDFA50- 927A-47D1-AD00-AF36943B8439 http://www.unitedstreaming.com/search/as setDetail.cfm?guidAssetID=7ABDFA50- 927A-47D1-AD00-AF36943B8439 http://www.unitedstreaming.com/search/as setDetail.cfm?guidAssetID=7ABDFA50- 927A-47D1-AD00-AF36943B8439

17 Thank you! The End!


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