Pulleys and Planes Simple Machines A machine is

Pulleys and Planes

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. Force is the capacity to do work or cause physical change. 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 simple pulley system – a single movable pulley lifting a unit weight. The tension in each line is half the unit weight.

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

Newton (N) § Unit used to measure force. § One newton is equal to the force needed to accelerate a mass of one kilogram one meter per second. § The symbol for newton is N.

The Inclined Plane § A sloping surface, such as a ramp.

The Inclined Plane § An inclined plane can be used to alter the effort and distance involved in doing work, such as lifting loads.

The Inclined Plane § The trade-off is that an object must be moved a longer distance than if it was lifted straight up, but less force is needed.

The Inclined Plane Bottom of a Bath Tub: Ramp:

The Inclined Plane Staircase: Screw:

The End!