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Simple Machines

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• Effort force acts on double the distance the load is raised = MA of 2 Effort force if half the weight of the load = MA of 2
• Overview only - next slide has more detailed explanation.
• First class levers: pop can, screw driver on lid, seesaw, catapult, pump handle Second Class: wheelbarrow, bottle cap, nut cracker Third Class: fishing pole, snow shovel, ice tongs/tweezers, chopsticks
• Simple Machines

1. 1. Simple Machines
2. 2. Simple Machines <ul><li>A machine is a device that makes work easier. </li></ul>
3. 3. Work & Machines <ul><li>A machine makes work easier by changing the direction or size of the force needed to move an object. (They cannot save or reduce work) </li></ul><ul><li>W = Force x distance </li></ul><ul><li>Two forces in simple machines: </li></ul><ul><ul><li>effort force </li></ul></ul><ul><ul><ul><li>the force applied to the machine to make it work </li></ul></ul></ul><ul><ul><li>resistance force </li></ul></ul><ul><ul><ul><li>the force resisting movement (often the object's weight, called the &quot;Load&quot;) </li></ul></ul></ul>
4. 4. Mechanical Advantage <ul><li>M.A. = resistance force </li></ul><ul><li> effort force </li></ul><ul><li>Multiplied force: </li></ul><ul><ul><li>A machine allows you to lift an 8N block with 4N of force </li></ul></ul><ul><ul><li>Mechanical Advantage = 8N/4N = 2 </li></ul></ul><ul><ul><ul><li>M.A. of 2 means your effort force is doubled </li></ul></ul></ul><ul><li>Change of direction: </li></ul><ul><ul><li>A machine lets you lift a 10 N block with 10 N of force </li></ul></ul><ul><ul><li>Mechanical Advantage = 10N/10N = 1 </li></ul></ul><ul><ul><ul><li>M.A. of 1 means the direction of your effort force is changed </li></ul></ul></ul>
5. 5. Inclined Plane <ul><li>Inclined plane : any flat, slanted surface </li></ul><ul><ul><li>A ramp is the most common type of inclined plane.  </li></ul></ul><ul><ul><ul><li>higher at one end than the other </li></ul></ul></ul><ul><ul><ul><li>the longer the ramp, the less force is needed to do the work </li></ul></ul></ul><ul><ul><li>Inclined planes help by pushing up against gravity's pull on the load (normal force). </li></ul></ul><ul><ul><ul><li>The load (resistance) moves in the same direction as the effort force. </li></ul></ul></ul>
6. 6. Inclined Plane Examples
7. 7. Wedge <ul><li>Wedge : two inclined planes put together to form a V-shape </li></ul><ul><ul><li>used to lift or pry apart heavy objects </li></ul></ul><ul><ul><li>can also stop an object from moving  </li></ul></ul><ul><li>A wedge works as the two inclined planes push at perpendicular angles on the load. </li></ul><ul><ul><li>The load moves in a different direction than the effort force. </li></ul></ul>In this picture, as the force moves the ax down, the load (wood) breaks apart and falls to the sides.
8. 8. Wedge Examples
9. 9. Screw <ul><li>Screw: an inclined plane wrapped around a center post </li></ul><ul><ul><li>longer inclined planes (more/closer threads) require less force to move the load </li></ul></ul><ul><ul><li>has two parts: the inclined plane and the center post  </li></ul></ul><ul><li>As the force rotates the screw, it goes down into the wood. </li></ul><ul><ul><li>The force and the load move in the same direction. </li></ul></ul><ul><ul><ul><li>Threads of screw increase surface area friction which allows screws to objects together better than nails  </li></ul></ul></ul><ul><ul><ul><li>Wedge-shaped post allows screw to go in wood easier </li></ul></ul></ul>
10. 10. Screw Examples
11. 11. Lever <ul><li>Lever: a straight bar that moves on a fixed point called a fulcrum. </li></ul><ul><ul><li>the longer the distance between effort force and the fulcrum, the less force will be needed to move the load  </li></ul></ul><ul><ul><li>has two parts: the bar and the fulcrum </li></ul></ul><ul><li>A lever works to change the direction of effort force and/or the distance the force acts throughout. </li></ul><ul><ul><li>Load & force move in opposite directions (1 st class lever) </li></ul></ul><ul><ul><ul><li>use gravity's pull on your own weight as the downward force </li></ul></ul></ul><ul><ul><li>Moving the fulcrum changes the distance needed to push down </li></ul></ul><ul><ul><ul><li>pushing the lever two feet down results in moving the rock up 1 foot </li></ul></ul></ul>
12. 12. Three Classes of Levers
13. 13. Levers <ul><li>First Class Lever: </li></ul><ul><ul><li>Fulcrum in middle, load & force on opposite ends </li></ul></ul><ul><ul><li>Load & force move in opposite directions .  </li></ul></ul><ul><li>Second Class Lever </li></ul><ul><ul><li>Load is in middle, with effort on end. </li></ul></ul><ul><ul><li>Load & force move in same direction .  </li></ul></ul><ul><li>Third Class Lever </li></ul><ul><ul><li>Bar is attached to fulcrum on one end. </li></ul></ul><ul><ul><li>Load is on end, with effort in middle. </li></ul></ul><ul><ul><li>Load & force move in same direction .  </li></ul></ul>
14. 14. Lever Examples
15. 15. Wheel & Axle <ul><li>Wheel and axle: a circular disc locked to a center post.  </li></ul><ul><ul><li>The larger the wheel, the less force needed to move the load. </li></ul></ul><ul><ul><li>two parts: the wheel and the center post (axle) </li></ul></ul><ul><ul><ul><li>When the wheel turns, it forces the axle to turn; or if the axle is turned, the wheel also turns. </li></ul></ul></ul><ul><ul><ul><li>One full turn of the large wheel results in one full turn of the smaller one. </li></ul></ul></ul><ul><li>The force moves in the same direction as the load.  </li></ul>
16. 16. Wheel & Axle Examples
17. 17. Pulley <ul><li>Pulley: a grooved wheel with a rope around it. </li></ul><ul><ul><li>The larger the wheel, the less force will be needed to move the load. </li></ul></ul><ul><ul><li>two parts: the wheel and the rope  </li></ul></ul><ul><li>  Pulleys can change the direction and/or amount of force needed to move the load. </li></ul><ul><ul><li>Load & force move in opposite or same directions, depending on how pulley is attached.  </li></ul></ul><ul><ul><li>As the rope is pulled down, the flag goes up. </li></ul></ul>
18. 18. Pulley Systems <ul><li>When used in combination, pulleys increase the mechanical advantage. </li></ul><ul><ul><li>To calculate the M.A., count the # of pulley ropes pulling on the load </li></ul></ul>
19. 19. Pulley Examples
20. 20. Efficiency <ul><li>Efficiency = output work </li></ul><ul><li> input work </li></ul><ul><li>No machine has 100% efficiency. </li></ul><ul><ul><li>Some work is lost due to friction </li></ul></ul><ul><ul><ul><li>Slows down work </li></ul></ul></ul><ul><ul><ul><li>Produces heat </li></ul></ul></ul><ul><ul><li>How can efficiency be increased? </li></ul></ul><ul><ul><ul><li>… by reducing friction </li></ul></ul></ul><ul><ul><ul><li>Lubricants (oil, grease, etc.) </li></ul></ul></ul>X 100%
21. 21. Calculating Efficiency <ul><li>Efficiency = output work </li></ul><ul><li> input work </li></ul><ul><li>If I swing a hammer and produce: </li></ul><ul><ul><li>Input 2,400 J of work </li></ul></ul><ul><ul><li>Output of 720 J of work </li></ul></ul><ul><ul><li>What is the efficiency of each swing? </li></ul></ul><ul><li>Efficiency = 720 J </li></ul><ul><li> 2,400 J </li></ul>X 100% X 100% = 30% efficient
22. 22. Review <ul><li>What is work? </li></ul><ul><ul><li>the transfer of energy that occurs when a force moves an object </li></ul></ul><ul><li>Equation for work? </li></ul><ul><ul><li>Work = Force x distance </li></ul></ul><ul><li>Units of work? </li></ul><ul><ul><li>Joules </li></ul></ul><ul><li>What is power? </li></ul><ul><ul><li>the rate at which work is done </li></ul></ul><ul><li>Equation for power? </li></ul><ul><ul><li>Power = Work  time </li></ul></ul><ul><li>Units of power? </li></ul><ul><ul><li>Watts </li></ul></ul>
23. 23. Review <ul><li>What is pressure? </li></ul><ul><ul><li>Amount of force applied to a unit of area. </li></ul></ul><ul><li>What formula do we use to calculate pressure? </li></ul><ul><ul><li>P = F/A </li></ul></ul><ul><li>What units are used to measure pressure? </li></ul><ul><ul><li>pascals (Pa) N/m 2 </li></ul></ul><ul><li>What is Pascal’s Principle? </li></ul><ul><ul><li>A force applied to a fluid in a closed container will cause an increase in pressure, equally transmitted to all parts of the fluid. </li></ul></ul><ul><li>How does depth affect pressure? </li></ul><ul><ul><li>Pressure also increases with depth. </li></ul></ul>
24. 24. Review Newton’s Laws Explanation Summary First Second Third