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MACHINES and EFFICIENCY

MACHINES and EFFICIENCY. Chapter 9.8-9.9. Key Terms. Work = Force x distance Simple machine a device used to multiply forces or change the direction of forces Compound machine A machine composed of two or more simple machines. Key Terms. Input (effort)

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MACHINES and EFFICIENCY

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  1. MACHINES and EFFICIENCY Chapter 9.8-9.9

  2. Key Terms • Work = Force x distance • Simple machine • a device used to multiply forces or change the direction of forces • Compound machine • A machine composed of two or more simple machines

  3. Key Terms • Input (effort) • Input distance: the distance you input the force when using a machine • Input force: the force you use when using a machine • Output (resistance) • Output distance: the distance the object that work is done on moves • Output force: the force required to move the object without a machine (usually the weight of the object in newtons)

  4. Key Terms • Mechanical Advantage (MA) • A unitless ratio that indicates the number of times a machine multiplies your input force • Ideal Mechanical Advantage (IMA) • The calculated MA, does not consider friction • Actual Mechanical Advantage (AMA) • The measured or real MA, does consider friction • Because of friction, AMA < IMA

  5. A simple machine • Multiplies and redirects force • Does not reduce the amount of work to be done, but makes work easier. • MA > 1 means that your input force will be less than your output force • More leverage means more mechanical advantage • If you increase MA, then • Input force will decrease • Input distance will increase

  6. Key Terms • Efficiency (a ratio) • Is calculated using the following equations: • Actual mechanical advantage/idealized mechanical advantage • Useful work output/total work input

  7. Key Terms • Efficiency of a machine decreases as friction increases • Friction increases the thermal energy by increasing molecular KE (non-mechanical energy) • In other words… friction causes the particles to speed up, raising the average KE of the particles (and temperature!) • Friction causes the useful work output to be less than the total work input

  8. Key Terms • When using a machine… • Work is done to move the object • Work is done against friction • Useful work output is the work done to move the object • Total work input is work done to move object + work done against friction

  9. Simple Machines • Two families Lever Inclined plane --Lever --Pulley --Wheel and axle --Ramp --Wedge --Screw

  10. LEVER FAMILY

  11. The Lever fulcrum

  12. Three Classes of Levers • First class Examples: Crowbar See-saw

  13. Three Classes of Lever • Second class Examples: Wheelbarrow Door

  14. Three Classes of Lever • Third class Examples: Human arm Baseball bat

  15. Calculating the Mechanical Advantage of a Lever • MA = input distance/output distance which is…MA = length of effort arm/length of resistance arm. Effort or input distance Resistance or output distance 0.5 m 2.5 m Resistance arm Effort arm

  16. Calculating the Mechanical Advantage of a Lever • 2nd class lever • 3rd class lever 2nd class levers decrease the input force but increase the input distance. 3rd class levers reduce the output force, but increase output distance and speed

  17. Which lever would have the highest mechanical advantage and why? b has the largest input distance, giving the largest MA c b a

  18. Pulley Fixed pulley 1 support rope IMA = 1

  19. Pulleys IMA = 2 Two supporting ropes

  20. Pulleys IMA = ? 2

  21. Pulley How many support ropes? 4 What is the IMA? 4

  22. Wheel and Axle • Wheel connected to a shaft GIVES YOU LEVERAGE

  23. INCLINED PLANE FAMILY

  24. Inclined planes • Ramps

  25. Wedge • Two inclined planes stuck together

  26. Screw • An inclined plane wrapped around a cylinder

  27. What type of machine is this? Compound: made of two or more machines Two 1st class levers; two wedges (scissor blades)

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