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Machines

Machines. Machine : a device that makes doing work easier by: a. changing the amount of force needed the distance which force is exerted the direction force is exerted. Mechanical Advantage. Machines change the way you do work Input force Effort force applied to do work

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Machines

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  1. Machines Machine: a device that makes doing work easier by: a. changing the amount of force needed the distance which force is exerted the direction force is exerted.

  2. Mechanical Advantage • Machines change the way you do work • Input force • Effort force applied to do work • Work done= input force X distance force moves machine • Output Force • Resistance force is work machine does • Should be greater than input…..or get a drill!!!! • Mechanical advantage = output/input • MA compares input to output • Number of times the input force is multiplied by a machine

  3. Force vs work • Work in= Effort force X Effort distance • Work out = Resistance force X Resistance distance • Work out can never be greater than the work in • But resistance force can be greater than effort force

  4. Example • To pry a lid off a paint can, you apply a force of 50 N to the handle of a screwdriver. What is the mechanical advantage of the screwdriver if it applies a force of 500N to the lid? • Output (resistance) force= 500N • Input (effort) force= 50N • Ma = ? • Ma= output/input = 500/50 = 10 The mechanical advantage of the screw driver is 10.

  5. Cheat sheet • If a machine lets you • Exert force over shorter distance (ex: rake) • Change in direction • Force and distance is not changed • Ma = 1, output=input **A simple machine which could have a mechanical advantage of 1is a pulley.

  6. Efficiency • Output < input • Why? Friction resistance • Friction up → Efficiency down • Being able to convert input to output is efficiency Efficiency = output work /input work X 100% Ideal machine has 100% efficiency Way to increase efficiency: oil up *** When you speak of efficiency, use percentages

  7. Work • Work = force X distance

  8. Mechanical Advantage Math • To open a bottle you apply a force of 50 N to a bottle opener. The bottle opener applies a force of 775N to the bottle cap. What is the mechanical advantage of the bottle opener? Finput= 50N Foutput= 775N Ma= ? Ma= Fo/Fi 775N/50N= 15.5

  9. Efficiency math • You do 100J of work in pulling out a nail with a claw hammer. If the hammer does 70 J of work, what is the hammer’s efficiency? Win= 100J Wout= 70J E= ? E= Wout/ Win X 100% E= 70J/ 100J X 100% = 70%

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