Lever: Difference between revisions
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==The three classes of levers== |
==The three classes of levers== |
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[[Image:LeverFirstClass.svg|thumb|First class lever]] |
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A first-class lever is a lever in which the fulcrum is located between the input effort and the output load. In operation, a force is applied (by pulling or pushing) to a section of the bar, which causes the lever to swing about the fulcrum, overcoming the resistance force on the opposite side. The fulcrum may be at the center point of the lever as in a seesaw or at any point between the input and output. This supports the effort maneets arm. |
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Examples: |
Examples: |
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# [[seesaw]] |
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# [[Trebuchet]] |
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# [[Crowbar (tool)|Crowbar]] (curved end of it) |
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# [[Claw hammer|Hammer Claw]], when pulling a nail with the hammer's claw |
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# [[Hand truck]]s are L-shaped but work on the same principle, with the axis as a fulcrum |
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# [[Shoehorn]] (used for putting feet into shoes) |
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# [[Spud bar]] (moving heavy objects) |
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# [[Beam engine]] although here the aim is just to change the direction in which the applied force acts, since the fulcrum is normally in the center of the beam (i.e. D1 = D2) |
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# [[Wheel and axle]] because the wheel's motions follows the fulcrum, load arm, and effort arm principle. |
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# [[Chopsticks| Chopsticks with hand]] the middle finger acts as a pivot. The whole system is a double lever. (Could also be seen as a third class lever, since the effort is between the fulcrum and the load) |
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Seesaw (also known as a teeter-totter) |
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Crowbar |
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[[Image:LeverSecondClass.svg|thumb|Second class lever]] |
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In a second class lever the input effort is located at the end of the bar and the fulcrum is located at the other end of the bar, opposite to the input, with the output load at a point between these two forces. |
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==Second Class Levers== |
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Examples: |
Examples: |
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# [[Bottle opener]] |
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# [[Crowbar (tool)|Crowbar]] (flat end) |
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# [[Curb bit]] |
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# [[Dental instruments#Elevators|Dental elevator]] |
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# [[Doorknob]] (could be a wheel and axle also) |
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# [[Nutcracker]] |
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# [[Oar]]: the water is the fulcrum; the boat is the load and the effort is at the inboard end<ref name="nolte">{{cite book|last=Nolte|first=Volker |title=Rowing faster|publisher=Human Kinetics|location=Champaign, IL|pages=145|isbn=9780736044653}}</ref> |
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# [[Press-up]] |
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# [[Spring board]] |
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# [[Torsion spring]], the main body handle exerts the incoming force |
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# [[Wrench]] |
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Nutcracker (double lever) |
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<!-- An internal link from [[Axe]] targets this paragraph directly. Please don't change the sub-heading without fixing the link as well. Thanks. --> |
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The handle of a pair of nail clippers |
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[[Image:ThirdClassLever.svg|thumb|Third class lever. For the lever in this diagram to work correctly, one must assume that the fulcrum is attached to the bar or acting in opposition to the other two forces.]] |
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An oar |
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For this class of levers, the input effort is higher than the output load, which is different from second-class levers and some first-class levers. However, the distance moved by the resistance (load) is greater than the distance moved by the effort. Since this motion occurs in the same length of time, the resistance necessarily moves faster than the effort. Thus, a third-class lever still has its uses in making certain tasks easier to do. In third class levers, effort is applied between the output load on one end and the fulcrum on the opposite end. |
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==Third Class Levers |
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Examples: |
Examples: |
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# [[Baseball bat]] |
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Tongs (double lever) (where hinged at one end, the style with a central pivot is first-class) |
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# [[Boat paddle]]<ref>{{cite book|last=Grimshaw|first=Paul |title=Sport and exercise biomechanics|publisher=Routledge|location=London|date=2006|isbn=9781859962848}}</ref> |
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Catapult |
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# [[Broom]] |
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Any number of tools, such as a hoe or scythe |
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# [[Electric gates|Electric gates]] |
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# [[Fishing rod]] |
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# [[Hammer]] |
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# [[Hockey stick]] |
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# [[Mandible]] |
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# [[Mousetrap|Mousetrap (Spring-loaded bar type)]] |
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# [[Shovel]] (the action of picking or lifting up sand or dirt) |
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# [[Stapler]] |
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# [[Tennis racket]] |
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# [[Tongs]] |
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# [[Tweezers]] |
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# [[Chopsticks| Chopsticks with hand]] (could also be seen as a first class lever, see above) |
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# [[Rake (tool)| Rake if the hand that is closer to the leaves is pushing]] |
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# [[Human Knee]] |
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==In the real world== |
==In the real world== |
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Revision as of 13:23, 11 January 2010
In physics, a lever (from French lever, "to raise", c.f. a levant) is a rigid object that is used with an appropriate fulcrum or pivot point to multiply the mechanical force that can be applied to another object. This leverage is also termed mechanical advantage, and is one example of the principle of moments. A lever is one of the six simple machines. Archimedes once said, "Give me a lever long enough and a fulcrum on which to place it, and I shall move the world." First class levers are similar but not the same as second or third class levers, in which the fulcrum, resistance, and effort are in different locations.
Early Studies
The earliest remaining writings regarding levers date from the 3rd century BC and were provided by Archimedes. Give me the place to stand, and I shall move the earth is a remark of Archimedes who formally stated the correct mathematical principle of levers (quoted by Pappus of Alexandria).
In ancient Egypt, constructors used the lever to move and uplift obelisks weighting more than 100 tons.
Force and levers
The force applied (at end points of the lever) is proportional to the ratio of the length of the lever arm measured between the fulcrum and application point of the force applied at each end of the lever. Mathematically, this is expressed by M = Fd.
The three classes of levers
There are three classes of levers representing variations in the location of the fulcrum and the input and output forces.
First-class levers
Examples:
Seesaw (also known as a teeter-totter) Crowbar Pliers (double lever) Scissors (double lever) Second-class levers
Second Class Levers
Examples:
Wheelbarrow Nutcracker (double lever) The handle of a pair of nail clippers An oar Third-class levers
==Third Class Levers
Examples:
Human arm Tongs (double lever) (where hinged at one end, the style with a central pivot is first-class) Catapult Any number of tools, such as a hoe or scythe The main body of a pair of nail clippers, in which the handle exerts the incoming force
In the real world
For the classical mechanics formulas to work, or to be a good approximation of real world applications, the lever must be made from a combination of rigid body|rigid bodies, i.e. a Beam (structure)|beam and a rigid fulcrum. Any bending or other Deformation (engineering)|deformation must be negligible.
See also
References
External links
- Lever at Diracdelta science and engineering encyclopedia
- A Simple Lever by Stephen Wolfram, Wolfram Demonstrations Project.
- Levers: Simple Machines at EnchantedLearning.com