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lever

 
Dictionary: lev·er   (lĕv'ər, lē'vər) pronunciation
 
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lever
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lever
top to bottom: first-class, second-class, and third-class levers
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n.
  1. A simple machine consisting of a rigid bar pivoted on a fixed point and used to transmit force, as in raising or moving a weight at one end by pushing down on the other.
  2. A projecting handle used to adjust or operate a mechanism.
  3. A means of accomplishing; a tool: used friendship as a lever to obtain advancement.
tr.v., -ered, -er·ing, -ers.

To move or lift with or as if with a lever.

[Middle English, from Old French levier, from lever, to raise, from Latin levāre, from levis, light.]


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Sci-Tech Encyclopedia: Lever
 
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A pivoted rigid bar used to multiply force or motion, sometimes called the lever and fulcrum (see illustration). The lever uses one of the two conditions for static equilibrium, which is that the summation of moments about any point equals zero. The other condition is that the summation of forces acting in any direction through a point equals zero. See also Inclined plane.

The lever pivots at the fulcrum.
The lever pivots at the fulcrum.

If moments acting counterclockwise around the fulcrum of a lever are positive, then, for a frictionless lever, FBb − FAa = 0, which may be rearranged to give Eq. (1).
1. F_B=\frac{a}{b}F_A
If FB represents the output and FA represents the input, the mechanical advantage, MA, is then given by Eq. (2).
2. {\rm MA}=\frac{F_B}{F_A}=\frac{a}{b}

Applications of the lever range from the simple nutcracker and paper punch to complex multiple-lever systems found in scales and in testing machines used in the study of properties of materials. See also Simple machine.

 
Dental Dictionary: lever
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(lev'ur)
n

A bar or rigid body that is capable of turning about one joint or axis and in which are two or more other points where forces are applied. There are three classes of levers, and each has its own most effective use.

 
Britannica Concise Encyclopedia: lever
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Simple machine used to amplify physical force. All early people used the lever in some form, for moving heavy stones or as digging sticks for land cultivation. Balance beams for weighing were probably used in Egypt c. 5000 BC; they consist of a bar pivoted at its center with weights on one end balancing the object on the other. As early as 1500 BC people were raising water and lifting soldiers over battlements using the swape or shadoof, a long lever pivoted near one end with a platform or container hanging from the short arm and counterweights attached to the long arm.

For more information on lever, visit Britannica.com.

 
Sports Science and Medicine: lever
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A bar or some other relatively rigid structure hinged at one point so that it can do work by rotating about an axis (the fulcrum or pivot) when a force is applied to it. In the human body, bones act as levers. The axis of a bone passes through a joint and it is moved by muscle forces (the effort) at the point of muscle attachment. The load consists of any resistance to movement. Sports implements, such as golf clubs and rackets, become levers when held in the hand. The usual function of a lever is to gain a mechanical advantage, whereby a small force applied over a large distance at one end of the lever produces a greater force operating over a smaller distance at the other end of the lever, or whereby a given speed of movement at one end of the lever is greatly increased at the other end. See also first class lever, second-class lever, third class lever.

 
Columbia Encyclopedia: lever
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lever, simple machine consisting of a bar supported at some stationary point along its length and used to overcome resistance at a second point by application of force at a third point. The stationary point of a lever is known as its fulcrum. The term lever is also applied to a projecting piece that is moved to operate or adjust inner machinery, such as a lever moved to the right or left to switch electric current on or off or to adjust the size of the opening of a shutter in a camera.

Principle of the Lever

It has been found by experiment that two equal forces acting in opposite directions, i.e., clockwise and counterclockwise, and applied to a uniform lever at equal distances from the fulcrum counteract each other and establish a state of equilibrium, or balance, in the lever. Experiment has also shown that two unequal forces when acting in opposite directions will bring about an equilibrium when the product of the magnitude of one force and its effort arm, or lever arm (the distance of its point of application from the fulcrum), is equal to the product of the magnitude of the other force and its effort arm. In physics the product of a force by its effort arm is called a moment of the force; the general conclusion known as the principle of moments states that equilibrium is established when the sum of the moments of the forces acting in a clockwise direction is equal to the sum of the moments of the forces acting in a counterclockwise direction. It is possible, as a result, to overcome a very large force at a short distance from the fulcrum with a very small force at a great distance from the fulcrum. Archimedes is supposed to have boasted, having the lever in mind, that given a place to stand he could move the world.

Classification and Application of Levers

In the use of a small force to overcome a large one the lever finds its many common applications. The lever is used for prying, as in the case of the crowbar, or for lifting. For example, the fulcrum is the point upon which a crowbar rests when used to lift or to pry loose some object; the effort is applied at the end farther from the fulcrum and is relatively small. The distance from the operator's hands to the fulcrum is known as the lever arm, or effort arm; the object being pried loose is the resisting force, or resistance; the object's distance from the fulcrum is the resistance arm. Levers in which the fulcrum is located between the effort and the resistance, as in the crowbar and the beam balance, are known as first-class levers. The fulcrum may also be located at one end of the lever, with the effort applied at the other end and the resistance in between; this type of lever, illustrated by the wheelbarrow and the nutcracker, is known as a second-class lever. The final possibility, known as a third-class lever, has the effort applied between the fulcrum and the resistance and is illustrated by various types of tongs.

Many other common tools, instruments, and appliances are applications of the principle of the lever. The human forearm is an application of the third-class lever, the elbow acting as the fulcrum, the weight held in the hand and being lifted as the resistance, and the pull of the muscles between the elbow and the hand as the effort. In a second-class lever, the effort arm is always longer than the resistance arm, so that a smaller effort moves a larger resistance, while in a third-class lever the reverse is always true, with the effort greater than the resistance. In a first-class lever, the effort may be either larger or smaller than the resistance, depending upon the location of the fulcrum.

 
Wikipedia: Lever
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This article is about the simple machine. For other uses, see Lever (disambiguation).
Levers can be used to exert a large force over a small distance at one end by exerting only a small force over a greater distance at the other.

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.

Contents

Theory of operation

The principle of the lever tells us that the above is in static equilibrium, with all forces balancing, if F1D1 = F2D2.

The principle of leverage can be derived using Newton's laws of motion, and modern statics. It is important to note that the amount of work done is given by force times distance. To use a lever to lift a certain unit of weight with a force of half a unit, the distance from the fulcrum to the spot where force is applied must be exactly twice that of the distance between the weight and the fulcrum. For example, to cut in half the force required to lift a weight resting 1 meter from the fulcrum, we would need to apply force 2 meters from the other side of the fulcrum. The amount of work done is always the same and independent of the dimensions of the lever (in an ideal lever). The lever only allows to trade force for distance.

The point where you apply the force is called the effort. The effect of applying this force is called the load. The load arm and the effort arm are the names given to the distances from the fulcrum to the load and effort, respectively. Using these definitions, the Law of the Lever is:

Load arm X load force = effort arm X effort force. If, for example, a 1 gram feather were balanced by a one kilogram rock, the feather would be 1000 times further from the fulcrum than the rock; if a 1 kilogram rock were balanced by another 1 kilogram rock, the fulcrum would be in the middle.

The three classes of levers

There are three classes of levers which represent variations in the location of the fulcrum and the input and output forces.

First-class levers

First class lever

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 arm.

Examples:

  1. Seesaw (also known as a teeter-totter)
  2. Trebuchet
  3. Crowbar (curved end of it)
  4. Hammer Claw , when pulling a nail with the hammer's claw
  5. Hand trucks are L-shaped but work on the same principle, with the axis as a fulcrum
  6. Pliers (double lever)
  7. Scissors (double lever)
  8. Shoehorn
  9. Spud bar (moving heavy objects)
  10. 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)
  11. Wheel and axle because the wheel's motions follows the fulcrum, load arm, and effort arm principle.

Second-class levers

Second class lever

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. Examples:

  1. Dental elevator
  2. Nutcracker
  3. Paddle
  4. Curb bit
  5. Wheelbarrow
  6. Wrench
  7. Bottle opener
  8. Diving Board (spring board)
  9. Crowbar (flat end)
  10. Push-up
  11. Doorknob(could be a wheel and axle also)
  12. Oars (the object is to move the boat, not the water).
  13. Tennis racket

Third-class levers

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.

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.

Examples

  1. Baseball bat
  2. Boat paddle
  3. Broom
  4. Electric Gates
  5. Fishing rod
  6. Hockey stick
  7. Mandible
  8. Mousetrap (Spring-loaded bar type)
  9. Nail clippers, the main body handle exerts the incoming force
  10. Shovel (the action of picking or lifting up sand or dirt)
  11. Stapler
  12. Tongs
  13. Tweezers
  14. Hammer


See also

External links

Sister project Wikimedia Commons has media related to: Levers
Sister project Look up lever in Wiktionary, the free dictionary.
v • d • e
Simple machine
Classical simple machines
Inclined plane · Lever · Pulley · Screw · Wedge · Wheel and axle

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

 
Translations: Lever
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Dansk (Danish)
n. - løftestang, stang, vægtstang
v. tr. - løfte med vægtstang, bruge som løftestang

Nederlands (Dutch)
hefboom, hendel, dommekracht, lichter, het uitoefenen van morele druk, hefboom bedienen, met hefboom verplaatsen

Français (French)
n. - (Aut, Tech) levier, manette, (fig) moyen de pression
v. tr. - utiliser/man¯uvrer un levier, (fig) installer/déloger qn

Deutsch (German)
n. - Hebel, Brechstange, Druckmittel
v. - hebeln

Ελληνική (Greek)
n. - μοχλός, χειρομοχλός, λεβιές
v. - κινώ με μοχλό, κινώ μοχλό

Italiano (Italian)
leva

Português (Portuguese)
n. - alavanca (f) (Téc.)
v. - mover ou erguer com alavanca, usar alavanca

Русский (Russian)
рычаг, средство воздействия, пользоваться рычагом

Español (Spanish)
n. - palanca, gato
v. tr. - levantar con palanca o gato, palanquear, hacer palanca

Svenska (Swedish)
n. - hävstång, spak, handtag, spett, hjälpmedel, vapen, tillhygge
v. - bända, använda hävstång, baxa

中文（简体）(Chinese (Simplified))
杠杆, 似杠杆之工具, 撬起, 移动, 用控制杆操纵

中文（繁體）(Chinese (Traditional))
n. - 槓桿, 似槓桿之工具
v. tr. - 撬起, 移動, 用控制桿操縱

한국어 (Korean)
n. - 지레 , 수단, 변속 레버
v. tr. - 지레로 움직이다, 지레로 삼다

日本語 (Japanese)
n. - てこ, レバー
v. - 動かす

العربيه (Arabic)
‏(الاسم) رافعه, مزل, عتله (فعل) يرفع, يحرك بمزل‏

עברית (Hebrew)
n. - ‮מנוף, לחץ מורלי‬
v. tr. - ‮הזיז במנוף, הניף‬

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Copyrights:

Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved.  Read more
Sci-Tech Encyclopedia. McGraw-Hill Encyclopedia of Science and Technology. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved.  Read more
Dental Dictionary. Mosby's Dental Dictionary. Copyright © 2004 by Elsevier, Inc. All rights reserved.  Read more
Britannica Concise Encyclopedia. Britannica Concise Encyclopedia. © 2006 Encyclopædia Britannica, Inc. All rights reserved.  Read more
Sports Science and Medicine. The Oxford Dictionary of Sports Science & Medicine. Copyright © Michael Kent 1998, 2006, 2007. All rights reserved.  Read more
Columbia Encyclopedia. The Columbia Electronic Encyclopedia, Sixth Edition Copyright © 2003, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/  Read more
Wikipedia. This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Lever".  Read more
Translations. Copyright © 2007, WizCom Technologies Ltd. All rights reserved.  Read more

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