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Chapter 5 Lesson 3

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**Types of Simple Machines**

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

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

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**Lever Le must be greater than Lr in order to multiply the force.**

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

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**Lever First Class Lever can increase force, distance, or neither**

changes direction of force

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Lever Second Class Lever always increases force

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Lever Third Class Levers always increases distance

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**Problems Lr Le Lr = 20 cm IMA = Le ÷ Lr Le = 80 cm**

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 = ? WORK: IMA = Le ÷ Lr IMA = (80 cm) ÷ (20 cm) IMA = 4 IMA Le Lr 20cm 100cm

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

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**Pulley Ideal Mechanical Advantage (IMA)**

equal to the number of supporting ropes IMA = 0 IMA = 1 IMA = 2

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**Pulley Fixed Pulley IMA = 1 does not increase force**

changes direction of force

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**Pulley Block & Tackle combination of fixed & movable pulleys**

increases force (IMA = 4) may or may not change direction

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

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**Pulley Movable Pulley IMA = 2 Multiplies force**

doesn’t change direction

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

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**Wheel and Axle Wheel and Axle**

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

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**Wheel and Axle Ideal Mechanical Advantage (IMA)**

effort force is usu. applied to wheel axle moves less distance but with greater force effort radius resistance radius

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

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**Mechanical Advantage of the Wheel and Axle**

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

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**Inclined Plane Inclined Plane Slanted surface used to raise objects h**

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Screw Screw inclined plane wrapped in a spiral around a cylinder

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**The Screw The IMA of a screw is related to the spacing of the threads.**

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.

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

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**Wedge Zipper 2 lower wedges push teeth together**

1 upper wedge pushes teeth apart

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

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

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Compound Machines 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. 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.

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Chapter: Work and Machines

Chapter: Work and Machines

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