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P. Sci.

P. Sci. Unit 3 Machines. What’s work?. A scientist delivers a speech to an audience of his peers. No A body builder lifts 350 pounds above his head. Yes A mother carries her baby from room to room. No A father pushes a baby in a carriage. Yes

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P. Sci.

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  1. P. Sci. Unit 3 Machines

  2. What’s work? • A scientist delivers a speech to an audience of his peers. • No • A body builder lifts 350 pounds above his head. • Yes • A mother carries her baby from room to room. • No • A father pushes a baby in a carriage. • Yes • A woman carries a 20 km grocery bag to her car? • No

  3. Copy this Machine – a device that makes doing work easier by…

  4. increasing the force that can be applied to an object. (car jack) Copy this

  5. increasing the distance over which the force can be applied. (ramp) Copy this

  6. by changing the direction of the applied force. (opening the blinds) Copy this

  7. Copy this • increasing the speed in which the work is done.

  8. Six Simple Machines Copy this • The six simple machines are: • Lever • Wheel and Axle • Pulley • Inclined Plane • Wedge • Screw

  9. Input Force FI Force applied to a machine Output Force FO Force applied by a machine Forces involved: Copy this

  10. Work Input work done on a machine =Input force x the distance through which that force acts (input distance) Work Output Work done by a machine =Output force x the distance through which the resistance moves (output distance) Two forces, thus two types of work Copy this

  11. Work output can never be greater than work input. Can you get more work out than you put in?

  12. Ideal machine Copy this Win = Wout 100% energy transfer. There is no such thing as an ideal machine – you always lose some energy (through friction, air resistance, etc.)

  13. Efficiency – a measure of how much of the work put into a machine is changed into useful output work by the machine. (less heat from friction) Copy this

  14. efficiency = (Wout / Win ) x 100% Win is always greater than Wout Copy this

  15. Mechanical Advantage • How much a machine multiplies force or distance output force (FR) • MA = input force (FE) Or input distance output distance Copy this

  16. The Lever Copy this • A bar that is free to pivot, or move about a fixed point when an input force is applied. • Fulcrum = the pivot point of a lever. • There are three classes of levers based on the positioning of the effort force, resistance force, and fulcrum.

  17. Lever Copy this MA = Length of effort arm Length of resistance arm Remember that Length is the same as distance or input distance output distance

  18. INPUT FORCE (EFFORT FORCE) OUTPUT FORCE (Resistance Force) INPUT ARM (EFFORT DISTANCE) OUTPUT ARM (RESISTANCE DISTANCE) FULCRUM

  19. Inclined Planes Copy this • Imagine how hard it would be to walk up the side of a steep hill. • It would be MUCH easier to follow a gentle slope of a winding trail….why is this? What is happening to input distance if you decide to take the curvy trail instead of going straight up the hill? Because input distance is greater than output distance, in this case, the input force is decreased…..so it’s easier for you!

  20. Inclined Plane MA = effort distance Resistance distance or input distance output distance Copy this

  21. Inclined Planes Copy this • Inclined plane: a slanted surface along which a force moves an object to a different elevation Input distance Output distance

  22. Inclined Planes • What is the MA of the following inclined plane? 6m 1 m Mechanical Advantage = 6 MA for inclined plane will NEVER be less than 1

  23. Wedges Copy this • Similar to inclined planes BUT sloping surfaces can move. • Wedge: a V-shaped object whose sides are two inclined planes sloped toward each other. Examples: knife, axe, razor blade

  24. The Screw Copy this • An inclined plane wrapped around a cylinder. • The closer the threads, the greater the mechanical advantage • Examples: bolts, augers, drill bits

  25. The Pulley Copy this • A chain, belt , or rope wrapped around a wheel. • Can either change the direction or the amount of effort force • Ex. Flag pole, blinds, stage curtain

  26. Pulley Copy this • The MA of a pulley or pulley system is equal to the number of pulleys supporting the load being lifted. • A single fixed pulley only changes the direction so MA = 1

  27. MA = Count # of pulleys in a row Fe

  28. Wheel & Axle Copy this • Consists of 2 discs or cylinders, each one with a different radius. wheel axle

  29. Compound Machines • A combination of two or more simple machines. • Cannot get more work out of a compound machine than is put in. Copy this

  30. Rube Goldberg Machines • Rube Goldberg machines are examples of complex machines. • All complex machines are made up of combinations of simple machines. • Rube Goldberg machines are usually a complicated combination of simple machines. • By studying the components of Rube Goldberg machines, we learn more about simple machines

  31. Safety Device for Walking on Icy Pavements When you slip on ice, your foot kicks paddle (A), lowering finger (B), snapping turtle (C) extends neck to bite finger, opening ice tongs (D) and dropping pillow (E), thus allowing you to fall on something soft.

  32. The End

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