Chapter 5 Lesson 3 Types of Simple Machines

Chapter 5 Lesson 3

Types of Simple Machines u A simple machine is a machine that does work with only one movement of the machine. u There are six types of simple machines: lever, pulley, wheel and axle, inclined plane, screw and wedge.

Lever u Lever l a bar that is free to pivot about a fixed point, or fulcrum Resistance arm Effort arm Fulcrum Engraving from Mechanics Magazine, London, 1824 “Give me a place to stand I will move the Earth. ” – Archimedes

Lever u Ideal Mechanical Advantage (IMA) l frictionless machine l MA greater than 1 increases force Effort arm length l Le Resistance arm length must be greater than Lr in order to multiply the force.

Lever u First Class Lever l can increase force, distance, or neither l changes direction of force

Lever u Second Class Lever l always increases force

Lever u Third Class Levers l always increases distance

Problems u You use a 100 cm plank to lift a large rock. If the rock is 20 cm from the fulcrum, what is the plank’s IMA? GIVEN: Lr = 20 cm Le = 80 cm IMA = ? Le IMA Lr WORK: IMA = Le ÷ Lr IMA = (80 cm) ÷ (20 cm) 20 cm IMA = 4 100 cm

Pulley u Pulley l grooved wheel with a rope or chain running along the groove l a “flexible first-class lever” F Le Lr

Pulley u Ideal Mechanical Advantage (IMA) l equal to the number of supporting ropes IMA = 0 IMA = 1 IMA = 2

Pulley u Fixed Pulley l IMA =1 l does not increase force l changes direction of force

Pulley u Block & Tackle l l l combination of fixed & movable pulleys increases force (IMA = 4) may or may not change direction

The Block and Tackle u The block and tackle shown has a IMA of 4.

Pulley u Movable Pulley IMA = 2 l Multiplies force l doesn’t change direction l

Movable Pulleys u For a fixed pulley, the distance you pull the rope downward equals the distance the weight moves upward. u For a movable pulley, the distance you pull the rope upward is twice the distance the weight moves upward.

Wheel and Axle u Wheel and Axle l two wheels of different sizes that rotate together l a pair of Wheel “rotating levers” Axle

Wheel and Axle u Ideal Mechanical Advantage (IMA) l l effort force is usu. applied to wheel axle moves less distance but with greater force effort radius resistance radius

Wheel and Axle u Doorknobs, screwdrivers, and faucet handles are examples of wheel and axles. u Usually the input force is applied to the wheel, and the output force is exerted by the axle.

Mechanical Advantage of the Wheel and Axle u A wheel and axle is another modified lever. u The center of the axle is the fulcrum. u The input force is applied at the rim of the wheel. u So the length of the input arm is the radius of the wheel.

Inclined Plane u Inclined Plane l Slanted surface used to raise objects l h

Screw u Screw l inclined plane wrapped in a spiral around a cylinder

The Screw u The IMA of a screw is related to the spacing of the threads. u The IMA is larger if the threads are closer together. However, if the IMA is larger, more turns of the screw are needed to drive it into some material.

Wedge u Wedge l a moving inclined plane with 1 or 2 sloping sides

Wedge u Zipper 2 lower wedges push teeth together l 1 upper wedge pushes teeth apart l

Compound Machines u Two or more simple machines that operate together form a compound machine. u A car is a compound machine. u Burning fuel in the cylinders of the engine causes the pistons to move up and down.

Compound Machines u This up-and-down motion makes the crankshaft rotate.

Compound Machines u The force exerted by the rotating crankshaft is transmitted to the wheels through other parts of the car, such as the transmission and the differential. u Both of these parts contain gears, that can change the rate at which the wheels rotate, the force exerted by the wheels, and even reverse the direction of rotation.