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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. • Makes work easier. • MA > 1 means that your input force will be less than your output force • If you increase MA, then • Input force will decrease • Input distance will increase

  6. Leverage and Mechanical Advantage • Increasing leverage refers to an increase in mechanical advantage

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

  8. LEVER FAMILY

  9. The Lever fulcrum

  10. Lever Output distance input distance 0.5 m 2.5 m Resistance arm Effort arm

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

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

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

  14. Pulley Fixed pulley 1 support rope IMA = 1

  15. Pulleys IMA = 2 Two supporting ropes

  16. Pulleys IMA = ? 2

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

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

  19. INCLINED PLANE FAMILY

  20. Inclined planes • Ramps

  21. Wedge • Two inclined planes stuck together

  22. Screw • An inclined plane wrapped around a cylinder

  23. What type of machine is this? Compound: made of two or more machines Two 1st class levers

  24. Key Terms • Efficiency (a ratio) • 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!)

  25. 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

  26. Calculating the Mechanical Advantage of a Lever • MA = Resistance force ÷ effort forceMA = length of effort arm ÷ length of resistance arm. 2.5 m 0.5 m Effort distance Resistance distance Resistance arm Effort arm

  27. Which lever would have the highest mechanical advantage? c b a

  28. 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

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