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Mechanical Advantage & Effeciency

Mechanical Advantage & Effeciency. Objectives. Explain how a machine makes work easier Describe and give examples of the force-distance trade-off that occurs when a machine is used Describe & Calculate mechanical advantage Describe & Calculate effeciency

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Mechanical Advantage & Effeciency

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  1. Mechanical Advantage & Effeciency

  2. Objectives • Explain how a machine makes work easier • Describe and give examples of the force-distance trade-off that occurs when a machine is used • Describe & Calculate mechanical advantage • Describe & Calculate effeciency • Explain why machines are not 100% efficient

  3. What is a machine? • Machines make work easier by • Changing the amount of force you exert • Changing the distance over which you exert the force • Changing the direction the force is exerted

  4. Which is easier? Opening a paint can with your fingers? Opening a paint can with a screwdriver? OR The force is multiplied and redirected.

  5. Which is easier? Pushing a heavy box up a ramp into a truck? Lifting a heavy box into a truck? OR The force is both multiplied and redirected.

  6. When using a machine to do work, two forces are involved. • Input Force (Fin) • The force you apply to the machine in doing work (Win) • Output Force (Fout) • The force that the machine applies in doing work (Wout)

  7. Two types of work are involved. • Work input is the amount of work done on a machine. • Input force x input distance • Work output is the amount of work done by a machine. • Output force x output distance Ideally, without friction Win = Wout (Fin) (din) = (Fout) (dout) How are the two related?

  8. Force-distance trade-off • To decrease the force needed, increase the distance • To increase the force needed, decrease the distance • Examples: wheelbarrow and hammer

  9. Force-Distance Trade-off(increases force) • Wheel barrow • Small force in a greater distance (lift handle of wheelbarrow) • Large force applied a shorter distance (load in wheelbarrow lifted)

  10. Force-Distance Trade-off(decreases force) • Hammer • Large force applied over a short distance • Small force applied over a long distance

  11. Measuring the benefits: Mechanical Advantage • Mechanical Advantage tells you how many times the machine multiples the force. • a machine with a large mechanical advantage can make lifting a heavy load easier Actual Mechanical Advantage (Reality) AMA = (Fout)/(Fin) Ideal Mechanical Advantage (No Friction) IMA = (din)/(dout)

  12. Calculating Mechanical Advantage • What is the mechanical advantage of a machine that applies 200N to an object when you apply 50N to the machine? Equation MA = (Fout)/(Fin) MA = (200N)/(50N) MA = 4

  13. Calculating Mechanical Advantage • You apply 2000 N to a machine and the machine applies 200 N to an object. What is the mechanical advantage? Equation MA = (Fout)/(Fin) MA = (200N)/(2000N) MA = 0.1

  14. Calculating Mechanical Advantage • You apply 10 N to a machine and the machine applies 10 N to another object. What is the mechanical advantage. Equation MA = (Fout)/(Fin) MA = (10N)/(10N) MA = 1 Can such a machine be useful?

  15. Mechanical Advantage:What does it mean? • Mechanical Advantage = 1 • There is no advantage to using the machine • Mechanical Advantage > 1 • The machine makes work easier • Mechanical Advantage < 1 • The machine makes work harder

  16. Efficiency • We said that the input work equals the output work, or: Win = Wout However, some output work is lost due to friction. • The comparison of work input to work output is called efficiency. • No machine has 100 percent efficiency due to friction. • What would improve the efficiency of a machine? (Hint: What reduces friction?)

  17. Calculating Efficiency • How efficient is a machine that takes 40 J of work and produces 30 J of work? Equation Eff = (Wout)/(Win) X 100% Eff = (30J)/(40J) X 100% Eff = 75%

  18. Calculating Efficiency You do 250,000 J of work to cut a lawn with a hand mower. If the work done by the mower is 200,000 J, what is the efficiency of the lawn mower? Equation Eff = (Wout)/(Win) X 100% Eff = (200,000J)/(250,000J) X 100% Eff = 80%

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