1 / 50

Demos

Demos. Nails and two pipes 8:40 ratio winch using Legos, string, and weights Lego gear box Pulley seat. Six fundamental devices used over and over in machines:. Wheel The Inclined Plane (wedge) Screw Lever Pulleys Gears (toothed wheels). The Wheel – found around 4000 B.C.

jett
Télécharger la présentation

Demos

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Demos • Nails and two pipes • 8:40 ratio winch using Legos, string, and weights • Lego gear box • Pulley seat

  2. Six fundamental devices used over and over in machines: • Wheel • The Inclined Plane (wedge) • Screw • Lever • Pulleys • Gears (toothed wheels)

  3. The Wheel – found around 4000 B.C. The first wheels were used as potters’ wheels. These wheels were found in archeological sites in and around Mesopotamia (modern Iraq). http://www.nationalarchives.gov.uk Wikipedia

  4. Flywheel • a heavy wheel for opposing and moderating (by its inertia) any fluctuation of speed in the machinery with which it revolves • a similar wheel used for storing kinetic energy (as for motive power) Merriam-Webster Online Inertia is the resistance to changes in motion. Inertia is proportional to mass. Heavy objects have inertia.

  5. 3500 B.C. the rolling wheel appears in Mesopotamia • Wheels greatly reduced the effort from having to slide heavy loads. • The wheel idea probably came from the use of rolling logs to carry loads.

  6. Wheel and Axle appear in 2000 B.C. in Egypt This early wheel is a solid, wooden disc that spins around a pole called the axle. http://www.ohtm.org/wheel.html Homo Sapiens have been around for 200,000 years. So humans survived without the wheel for many thousands of years.

  7. Domestication of large animalsexploits the usefulness of wheelsleading to the beginning of agrarian societies • Jared Diamond identifies only 14 domesticated large mammal species worldwide. The five most useful (cow, horse, sheep, goat, and pig) are all descendants of species from Eurasia. Of the remaining nine, only two (the llama and alpaca both of South America) are indigenous to a land outside the temperate region of Eurasia. • What does this mean for Native Americans, Africans, Australians, and most South Americans? • Culture and technological progress depends on an advantageous geography. UC Berkeley

  8. Large continuous Temperate zone in which domesticated animals could evolve and spread out. Eurasia Shown in pink are the Temperate Zones having Four Seasons and Grasslands. Wikipedia

  9. Machines with rotary motion have wheels. Wheels transmit forces. • Your car’s crankshaft • Water Turbine • Steering Wheel • Water Meter • Can Opener • A Winch • A Clock’s Hands • Car Wheels • Sewing Machine • Flywheel in lawnmower engine Palm Springs Hand Winch Grist Mill in Napa Valley

  10. The Wheel The axle rotates with more turning force (torque) than the wheel, but the wheel travels a larger distance than the axle. More on this after we get to Levers Wheel, where gear teeth are. Axle – where rope is taken up The Winch www.m-w.com/mw/art/winch.gif

  11. http://www.answers.com/topic/steering-wheel-ship Brake Pads apply a force at the perimeter of the wheel. Why are ship wheels so large?

  12. The Inclined Plane (Wedge) • The Inclined Plane is a ramp. • Builders may have used earthen ramps to place lintels when constructing Stonehenge around 2800 B.C. Stonehenge

  13. Egyptians used ramps to construct the Pyramids circa 2000 B.C. Lehner, Mark. The Complete Pyramids

  14. How does the Inclined Plane Work? It takes a fixed amount of work to move something from one point to another. Work = Force x Distance By increasing the distance, the same amount of work can be done with less force (less effort).

  15. Twice the Distance, half the Effort (force). Full Effort (full force) and shortest path for raising the object.

  16. The mechanical advantage of a ramp is given by the ratio of its length to its width In physics and engineering, mechanical advantage (MA) is the factor by which a machine multiplies the force put into it. education.jlab.org

  17. The Arrowhead is a sharp wedge Broken arrowhead found summer of 2007 along a lake beach at 7500 feet in the Sierras. This technology is prehistoric, developed maybe 30,000-50,000 B.C.

  18. How does a Wedge Work? • A wedge or arrowhead is a moving inclined plane. • The wedge separates whatever it is pushed or shot into. • Examples are knives and axes. • Wedges can also hold things, like door-stops

  19. Big Force, Small Separation Smaller force, larger Distance The classroom doorstop works the same way. As the doorstop is pushed under the door, the wedge pushes the door up. The door pushes back on the wedge. This large force causes the wedge to grip the floor.

  20. The Plow is a metal wedge that cuts furrows into the soil The Sumerians used handheld wooden plows, but this technique failed in heavy, wetter, harder soils, such as those in Europe. Sumerians lived in Mesopotamia (Modern day Iraq) Wisconsinhistory.org

  21. Romans developed a metal blade and added a wheel (100 A.D.) The plow’s blades cut and then turned over the topsoil, creating a furrow for planting.

  22. Using oxen to pull the plow the Romans were able to cultivate much more land Romans exported agricultural products using wagons and weather-proof roads.

  23. The ScrewA spiraling inclined plane • Any material traveling in a screw (sawdust, water) has to turn multiple times to move forward a short distance. • Since the distance is increased, the effort needed to move the material is reduced. Screw Conveyor ContinentalScrew.com

  24. education.jlab.org MA of an screws can be estimated by dividing the number of turns per inch.

  25. Recall the “Apple Lathe” An apple spiraling through the coring blade takes less force (but many rotations) than pushing the apple straight through a blade.

  26. What prompted the need for the screw? • Once water was channeled into irrigation ditches, how could the water be brought up to the fields? • Before the screw, laborers used Shadufs. (shadoo) Shaduf

  27. Archimedes, a prolific Greek inventor is credited with coming up with the screw as a means of moving water uphill in 235 B. C. Wikipedia

  28. How did Archimedes figure this out? • Lifting along an inclined plane is easier than lifting something straight up. • The spiral is a type of incline wrapped around a cylinder. • By placing a screw at a low angle, water can be made to flow up – at some point along the screw’s cylinder water is flowing downstream.

  29. Screws and Augers Today Augers are devices designed for moving material. Modern Augers used to drain the Polders in Holland Wikipedia

  30. The Lever • The Lever is a rigid bar that rotates around a fixed point (fulcrum). • People figured out that it was easier to lift a heavy object by wedging a board under the object and then pushing down on the other end of the board. First class lever with fulcrum in the center. US Dept of Transportation

  31. First Class Levers – fulcrum in middle • SeeSaws • Scales • Dollie • Crowbars • Scissors • Pliers All these levers have their Fulcrum between the load and effort.

  32. Effort Load Fulcrum Archimedes explained the math behind the Lever Effort x Distance of the effort from the Fulcrum = Load X Distance of the load from the Fulcrum This equation assumes the lever is not moving.

  33. Effort Load Torque due to Effort Torque due to Load Fulcrum Torque: a twisting or spinning force Torque = Lever Arm X Force (Lever Arm is measured as the distance from the load/effort to the Fulcrum) When two torques are equal and opposite the lever arm does not move.

  34. “If you give me a lever and a place to stand, I can move the world” Archimedes • Stonehenge • Easter Island Statues • Pyramids Statues around Easter Island, Chile. The theory is the statues were moved by being rocked back and forth 400-1000 years ago. Wikipedia

  35. Second Class LeversLoad is between the Fulcrum and Effort • Wheelbarrow • Bottle Opener • Nut Cracker • Tortilla Press Royal Prestige Tortilla Press

  36. What is the MA of the potato ricer? • Find distance from fulcrum to potato. • Find distance from fulcrum to your hand. • The ratio is the MA, or about 4. • Force on the potato is 4X the force you apply with your hand.

  37. Third Class LeversThe Effort is between the Fulcrum and the Load • Tweezers • Hammer (here the objective is to get the massive end of the hammer to move faster than your hand) • Fishing Pole (here the objective is to quickly pull the fish out with only small movements of your hands) Clockmaker’s Tweezers

  38. A Winch is a rotating lever? The hub (center) of the winch is the Fulcrum. The handle moves a greater distance than the spool where rope is taken in. The spool turns with more force (torque) but moves a smaller distance than the handle.

  39. The Winch A small force applied over a large distance causes the center of the winch to turn with greater force, but more slowly. http://www.cvfsupplycompany.com

  40. A Wheel is a rotating lever? The hub (center) of the wheel is the Fulcrum. The outside of the wheel moves a greater distance than the axle. Larger wheels cover a greater distance than smaller wheels at the same rpm (revolutions/minute) Road bicycles have larger wheels than mountain bikes because road bikes are designed for speed and comfort.

  41. Pulleys Mechanical Advantage the factor by which a mechanism multiplies the force put into it

  42. Pulleys • A pulley is a grooved wheel that a cable runs through. • The Pulley on the left is a first class pulley. The force needed to move the load is equal to the weight of the load. This has a mechanical advantage of 1. Force=Load • The Pulley on the right is a second class pulley. The force needed to raise the load is half but the load moves at half the speed of the rope. This pulley has a mechanical advantage of 2. The force is doubled.

  43. Tension in the rope is uniform. Second pulley used to direct Force downward. This combines a first-class and a second-class pulley Wikipedia

  44. Mechanical Advantage Of 3. Mechanical Advantage Of 4. Wikipedia

  45. Gears http://www.geocities.com

  46. Gears are good for: • Increasing Torque & Decreasing Rotational Speed • (known as gear or speed reduction) • Decreasing Torque & Increasing Rotation Speed • (known as torque reduction) • Changing the direction of the motion. http://science.howstuffworks.com/gear.htm Refer to this url for useful info on gears.

  47. Force is the same where teeth touch. Example of Torque reduction: Gear B turns twice as fast as Gear A, but Gear B turns with ½ the torque compared to Gear A. Torque is the turning force. Torque = F X (distance from teeth to axle)

  48. Example of Speed Reduction: Gear B turns with three times the torque as Gear A, but at 1/3 the speed.

  49. This is speed reduction. The driver A turns 4 times faster than gear B, but the load gear turns with 4 times the torque. The force at the teeth is the same for both wheels. Since the load gear has a radius 4 times bigger than the driver, the torque is 4 times bigger for the big gear. MA = 4 If you put a handle on Gear A, could this be a winch?

  50. Resources • http://brunelleschi.imss.fi.it/genindice.asp?appl=LIR&indice=63&xsl=listagenerale&lingua=ENG&chiave=100799 • http://science.howstuffworks.com/

More Related