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Simple machines

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  • 1. Honors Physics Simple machines The following notes are NOT in your textbook!
  • 2. What is a simple machine? • All machines are devices that make work easier • Some do by using other energy sources: electricity, gas, etc. • Simple machines make work easier, are often human powered, and have minimal moving parts
  • 3. Examples of simple machines We will focus on inclined planes and pulleys
  • 4. What do simple machines do? • They make it easier to do the SAME amount of work, but they do not actually make the amount of work LESS – they make the input force required to do the work less! • For example: you may not be able to lift a snow blower onto the bed of a truck yourself, but you could do it using a ramp • Exert a smaller force over a greater distance • You end up doing the same amount, or even more work (real world has friction!)
  • 5. Less force applied over a longer distance FFinin FFoutout dout din Θ
  • 6. Mechanical advantage • Definition: The number of times a machine can multiply the input (or effort) force • Actual Mechanical Advantage: It takes into account real-world factors like friction. It is the ratio of the output force and the input force. AMA = Output force Input force • Ideal Mechanical Advantage: the MA of an “ideal machine” with 100% efficiency. It is the ratio of the distances through which the forces must move in a simple machine. IMA = Input Distance Input force
  • 7. Work input & output • The same work equation still applies… The work that YOU put in… Win = FinXin The work done by the machine… Wout = FoutXout • Simple machines are never 100% efficient due to friction, so we also calculate their efficiency. Efficiency =(Wout/ Win)x 100 = (AMA / IMA) x 100
  • 8. Simple machines: inclines • It takes 100 N of force to pull a box that weighs 300 N up a ramp into the back of a pick up truck. If the ramp is 5 meters long, and the height of the pickup truck is 1.0 meter, calculate: (a) The work input (b) The work output (c) The AMA of the ramp (d) The IMA of the ramp (e) The efficiency of the ramp FFinin FFoutout dout Din Θ 500 J 300 J 2 5 60%
  • 9. Simple machines: Pulleys • Pulleys divide the load force over a number of ropes • MA = # of strands that are lifting upwards (not counting the force you apply if you pull down to lift the load)
  • 10. Pulleys lab • Each group will need: 10 Newton spring scale, 200 gram mass, 500 gram mass, string, metric ruler (a) 1 pulley, 1 s-hook (b) 1 pulley, 1 s-hook (c) 2 single pulleys, 2 s- hooks (d) 2 double pulleys, 2 s- hooks