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Using Machines

Using Machines. Chapter 4: Section 2. Machine - device that makes doing work easier They change the way a person does work, not the amount of work that needs to be done. When using a machine, the output work can never be GREATER than the input work

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Using Machines

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  1. Using Machines Chapter 4: Section 2

  2. Machine- device that makes doing work easier • They change the way a person does work, not the amount of work that needs to be done

  3. When using a machine, the output work can never be GREATER than the input work • A machine cannot do more work than you put in! • Law of conservation of energy • Do not get work confused with force!

  4. Mechanical Advantage- number of times the input force is multiplied by a machine • MA = output force = Newtons input force Newtons Or: MA = Fout Fin The UNITS cancel out!

  5. Fin = Input force- the effort, or force you exert on a machine • Fout = Output force-the force exerted by the machine

  6. A Machine Makes Work Easier by: • Changing the amount of force needed • Changing the distance the force covers • Changing the direction of the force

  7. Changing the Force • Some machines allow you to exert a smaller force over a longer distance • Output force > input force, resulting in a MA > 1 • Ex: a ramp Output force = 500N = 10 Input force 50N

  8. Changing the Distance • Some machines allow you to exert your force over a shorter distance • Output force < Input force, resulting in a MA < 1 • Ex. A rake Output force = 10N = 0.1 Input force 100N

  9. Changing the Direction • Some machines allow you to change the direction of the input force • Output force = input force, resulting in MA = 1 • Ex. pulley Output force = 50N = 1 Input force 50N

  10. Efficiency – ability of a machine to convert input work to output work Efficiency = output work input work x 100% Or: Eff = Woutx 100% Win Answer will always be in a percentage!

  11. Using a pulley system, acrew does 7500 J of work to lift a lead a box. The pulley system completes4500 J of work. What is the efficiency of the pulley system? Wout = 4500 J Win = 7500 J Eff = _____ Eff = Woutx 100% Win Eff = 4500 Jx 100% 7500 J Eff = 0.6 x 100% Eff = 60%

  12. Friction – reduces efficiency by converting some work into heat. • The efficiency of a real machine is always less than 100% because of friction. • Only ideal machines are 100% efficient • Oil, or another lubricant can increase efficiency by reducing the number of contact points between surfaces.

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