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Simple Machines

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- 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.

- Hence, Finputdinput = Foutputdoutput
- 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.

- 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

- 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).

- 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).

- 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?

- 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).

- Be careful with change of force direction strand!

- 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

- 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.

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?

- 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