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:
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.