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# Simple machines

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### Simple machines

1. 1. Honors Physics Simple machines The following notes are NOT in your textbook!
2. 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. 3. Examples of simple machines We will focus on inclined planes and pulleys
4. 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. 5. Less force applied over a longer distance FFinin FFoutout dout din Θ
6. 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. 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. 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. 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. 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