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Simple Machines

Simple Machines. There are 6 basic simple machines. Simple machine do not decrease the amount of work we must do, they make the work easier by decreasing the amount of force we must apply. W I nput = W Output. Hence, F input  d input = F output  d output

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Simple Machines

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  1. Simple Machines • There are 6 basic simple machines. • Simple machine do not decrease the amount of work we must do, they make the work easier by decreasing the amount of force we must apply.

  2. WInput = WOutput • Hence, Finputdinput = Foutputdoutput • Notice that cos(θ) has been omitted since the direction of motion and force is 0. • Also, notice that all of these may have different names such as effort, load or resistance.

  3. Remember in all these cases the Winput = Woutput • Thus the man above applies a small force (FI) over a big distance (dI) while the rock moves upward with big force (FO) over a small distance (dO). Fd Fd

  4. Mechanical Advantage • Is the amount a machine amplifies an applied force. • Hence, a you would only need to apply 50 N of force to a machine with MA = 2 in order to lift 100 N. • Ideal mechanical advantage (IMA) is the advantage gained by a 100 % efficient machine (i.e. no friction). • MA can always be determined by dividing the Foutput by the Finput (however, certain simple machines have other ways of determining this value).

  5. Levers • 3 types: • Class 1 – Fulcrum is between the effort and the load (scissors, crowbar). • Class 2 – Load is between the fulcrum and the effort (wheelbarrow, bottle opener). • Class 3 – Effort is between the fulcrum and the load (tweezers, your arm).

  6. Another way of determining the MA of a lever is to divide the effort length by the resistance length. Problem 1: (a) A lever used to lift a heavy box has an input arm of 4 meters and an output arm of 0.8 meters. What is the mechanical advantage of the lever? (b) If you pushed down with 20 N of force over a distance of 0.80 m how much work did you accomplish? (c) How high was the box raised? (d) What is the mass of the box? Problem 2: A broom with an input arm length of 0.4 meters has a mechanical advantage of 0.5. What is the length of the output arm?

  7. Pulley • Is really just a glorified lever! • MA is determined by counting the number of supporting strands (subtract one if the strand just changes the direction of the applied force).

  8. Be careful with change of force direction strand!

  9. In each of these pulley systems find: • the MA • the effort force • the amount of rope that must be pulled to raise the load 0.50 m

  10. Inclined Plane/Ramp • The output work of the load is the vertical distance traveled or mgh. • The MA can be determined by dividing the length of the ramp by its vertical height.

  11. Practice Problems • A 5 meter ramp lifts objects to a height of 0.75 meters. What is the mechanical advantage of the ramp? • How much work would be required to bring a 10 kg object to the top of this ramp? • What would be the input force required to use this ramp? • Gina wheels her wheelchair up a ramp using a force of 80 N. If the ramp has a mechanical advantage of 7, what is the output force? • A mover uses a ramp to pull a 1000 N cart up to the floor of his truck (0.8 m high). If it takes a force of 200 N to pull the cart, what is the length of the ramp?

  12. Image Sources • http://capocci.pbworks.com/w/page/22877939/Simple%20Machines • http://www.science-class.net/Notes/Notes_simple_machines_7th.htm • http://campus.murraystate.edu/academic/faculty/tderting/atlases2009/runyon/Whatlever.html • http://etc.usf.edu/clipart/35900/35944/lever_35944.htm • http://www.pbs.org/wgbh/nova/teachers/activities/27po_sle2phar.html • http://hyperphysics.phy-astr.gsu.edu/hbase/mechanics/lever.html • http://en.wikipedia.org/wiki/Mechanical_advantage_device • http://hyperphysics.phy-astr.gsu.edu/hbase/mechanics/lever.html • http://www.schoolphysics.co.uk/age11-14/Mechanics/Forces%20in%20motion/text/Pulleys_/index.html • http://www.phy.ilstu.edu/pte/489.01content/simple_machines/simple_machines.html • http://road-to-psle.blogspot.com/2008/10/simple-machines-incline-plane.html

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