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Unit 6 – Lecture 1

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Review Work = Force * distance measured in Joules [newton meters] this remains true using effort force or resistance force Power = Work / time measured in Joules per second Mechanical Advantage = Force (out) / Force (in) Efficiency = Work (out) / Work (in) * 100

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Machines A Simple Machine accomplishes the work in one motion. A Compound Machine is made up of two or more simple machines. Most machines are compound machines.

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Simple Machines There are six types of simple machines: Lever Wheel-and-Axle Pulley Inclined Plane Wedge Screw

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Helpful Note ALL of the equations for the mechanical advantage of different types of machines will be given to you for the test [which will take place tentatively on Monday, 2/8]. Ideal vs. Actual Mechanical Efficiency Ideal = according to the equation Actual = taking into account the efficiency ex: MA = 2 but machine only has a 94% efficiency 2 = the ideal MA 2*.94 = actual efficiency. MA = 1.88

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Lever A Lever is comprised of: a bar (straight or curved) a fixed point called the fulcrum on which the bar pivots Bar Fulcrum

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Lever The distance from where the effort force is applied to the fulcrum is the Effort Arm of the lever. this is where your effort is done Effort Arm

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Lever The distance from the fulcrum to where the resistance force is applied is the Resistance Arm. Resistance Arm

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Lever There are three classes of levers: class is determined by where the location of the effort force, resistance force (load), and the fulcrum

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Lever 1 st class lever: see-Saw (Teeter-Totter) prying up a lid by pushing down on a bar pairs: scissors, pliers, hedgeclippers

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Lever 2 nd class lever: door wheelbarrow arms pairs: shears, nutcracker

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Lever 3 rd class lever: NOTE: MA = < 1 effort increases to increase distance of load tweezers! anything you swing bat, sword, stick, golf club brooms, rakes, mops

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MA Lever The MA of a lever is calculated as: MA Lever = Effort Arm Resistance Arm (again, both in units of length, so there are no MA units) The longer the effort arm, the more the MA [the better it is for you] recall: increase distance, less force

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Practice What is the MA of a lever with an Effort Arm of 6 m and a Resistance Arm of.3 m? Which type of lever does not increase the force output of the machine? If a lever has a MA of 9, and a force of 6 N is applied, how much force will the lever apply?

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Wheel-and-Axle Wheel & Axle - a simple machine made of two circles of different diameters that rotate together. The outer circle (wheel) is turned with less force over a larger distance so that the inner circle (axle) turns with more force over a shorter distance. Ex. Steering wheels, door knobs, faucet handles

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MA Wheel&Axle MA = radius Wheel radius Axle Explains how to steer larger vehicles with less force

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Practice What is the MA of a Wheel with a 50 cm radius connected to an Axle with a 2.5 cm radius?

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Pulley Pulley - a simple machine comprised of a wheel with a rope or chain running around it. The MA of a pulley system is equal to the number of ropes which support the object, because the weight is distributed. MA = 1 no difference MA = 2 no difference MA = 3 no difference MA = 4 no difference

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Pulley There are two types of pulleys Fixed do not move, merely redirect force Moveable attached to the object being pulled and multiply force rises and falls with the object

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Pulley Block and Tackle System - a multiple-pulley system where large amounts of distance are converted into force. composed of a fixed pulley & a moveable pulley MA = number of supporting ropes

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Practice What is the MA of this pulley system? 2 What is the effort force? [give in pounds of force] 35 lbs

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Practice What is the MA of this pulley system? 3 What is the effort force? [give in pounds of force] 23.3 lbs

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Practice What is the Force Output of this pulley system? 50 N

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