lever
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first-class, second-class, and third-class levers (Precision Graphics) |
n.
- 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.
- A projecting handle used to adjust or operate a mechanism.
- A means of accomplishing; a tool: used friendship as a lever to obtain advancement.
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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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 5000 ; they consist of a bar pivoted at its center with weights on one end balancing the object on the other. As early as 1500 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.
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.
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. 
If FB represents the output and FA represents the input, the mechanical advantage, MA, is then given by Eq. (2).
2. 
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.
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:
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lever
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.
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(lev'ur)
n
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.
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categories related to 'lever'
- Machinery and Mechanical Devices - lever: simple machine: rigid bar that transmits or modifies lifting force applied at one point and is supported by fulcrum at a fixed point
- Building and Machine Parts - lever: bar used to lift heavy object or pry open something
- Shovels and Digging and Lifting Tools - lever: rigid bar on axis or fulcrum, used to lift weight or exert pressure to dislodge something
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This article is about the simple machine. For other uses, see Lever (disambiguation).
| Lever, one of the six simple machines | |
|---|---|
 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. |
|
| Classification | Simple machine |
| Industry | Construction |
| Weight | Mass times gravitational acceleration |
| Fuel source | potiential and kinetic energy {mechanical energy } |
| Components | fulcrum or pivot, load and effort |
A lever (
/ˈlɛvər/ or UK /ˈliːvər/) is constructed from a beam attached to ground by a hinge, or fulcrum. It is one of the six simple machines identified by Renaissance scientists. The word comes from the French lever, "to raise", cf. a levant. A lever amplifies an input force to provide a greater output force, which is said to provide leverage. The ratio of the output force to the input force is the ideal mechanical advantage of the lever.
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Contents
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Early use
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The earliest remaining writings regarding levers date from the 3rd century BC and were provided by Archimedes. "Give me a place to stand, and I shall move the Earth with a lever"[note 1] is a remark of Archimedes who formally stated the correct mathematical principle of levers (quoted by Pappus of Alexandria).[1]
It is assumed that in ancient Egypt, constructors used the lever to move and uplift obelisks weighting more than 100 tons.[2]
Force and levers
A lever is a beam connected to ground by a hinge, or pivot, called a fulcrum. The ideal lever does not dissipate or store energy, which means there is no friction in the hinge or bending in the beam. In this case, the power into the lever equals the power out, and the ratio of output to input force is given by the ratio of the distances from the fulcrum to the points of application of these forces. This is known as the law of the lever.
Mathematically, this is expressed by 
, where 
is the force, 
is the perpendicular distance between the force and the fulcrum, and 
is the turning force known as the moment or torque.
Classes of levers
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Levers are classified by the relative positions of the fulcrum and the input and output forces. It is common to call the input force the effort and the output force the load or the resistance. This allows the identification of three classes of levers by the relative locations of the fulcrum, the resistance and the effort:[3]
- Class 1: Fulcrum in the middle: the effort is applied on one side of the fulcrum and the resistance on the other side, for example, a crowbar or a pair of scissors or a seesaw.
- Class 2: Resistance in the middle: the effort is applied on one side of the resistance and the fulcrum is located on the other side, for example, a wheelbarrow or a nutcracker or a bottle opener.
- Class 3: Effort in the middle: the resistance is on one side of the effort and the fulcrum is located on the other side, for example, a pair of tweezers or the human mandible.
These cases are described by the mnemonic "fre 123" where the fulcrum is in the middle for the 1st class lever, the resistance is in the middle for the 2nd class lever, and the effort is in the middle for the 3rd class lever.
Law of the lever
The lever is a movable bar that pivots on a fulcrum attached to a fixed point. The lever operates by applying forces at different distances from the fulcrum, or pivot.
Assuming the lever does not dissipate or store energy, the power into the lever must equal the power out of the lever. As the lever rotates around the fulcrum, points farther from this pivot move faster than points closer to the pivot. Therefore a force applied to a point farther from the pivot must be less than the force located at a point closer in, because power is the product of force and velocity.[4]
If a and b are distances from the fulcrum to points A and B and let the force FA applied to A is the input and the force FB applied at B is the output, the ratio of the velocities of points A and B is given by a/b, so we have the ratio of the output force to the input force, or mechanical advantage, is given by
This is the law of the lever, which was proven by Archimedes using geometric reasoning.[5] It shows that if the distance a from the fulcrum to where the input force is applied (point A) is greater than the distance b from fulcrum to where the output force is applied (point B), then the lever amplifies the input force. On the other hand, if the distance a from the fulcrum to the input force is less than the distance b from the fulcrum to the output force, then the lever reduces the input force.
The use of velocity in the static analysis of a lever is an application of the principle of virtual work.
See also
- Engineering mechanics
- Heavy equipment
- Linkage (mechanical)
- Mechanical advantage
- Mechanism (engineering)
- Virtual work
Notes
- ^ If this feat were attempted in a uniform gravitational field with an acceleration equivalent to that of the Earth, the corresponding distance to the fulcrum which a human of mass 70kg would be required to stand to balance a sphere of 1 Earth mass, with center of gravity 1m to the fulcrum, would be roughly equal to 8.5×1022m [1]. This distance might be exemplified in astronomical terms as the approximate distance to the Circinus galaxy (roughly 3.6 times the distance to the Andromeda Galaxy) - about 9 million light years.
References
- ^ Mackay, Alan Lindsay (1991). "Archimedes ca 287–212 BC". A Dictionary of scientific quotations. London: Taylor and Francis. p. 11. ISBN 978-0-7503-0106-0.
- ^ Budge, E.A. Wallis (2003). Cleopatra's Needles and Other Egyptian Obelisks. Kessinger Publishing. p. 28. ISBN 978-0-7661-3524-6.
- ^ Davidovits, Paul (2008), Physics in Biology and Medicine, Third edition, Academic Press, p. 10, ISBN 978-0-12-369411-9, http://books.google.be/books?id=e9hbt3xisb0C, Chapter 1, p. 10
- ^ Uicker, John; Pennock, Gordon; Shigley, Joseph (2010). Theory of Machines and Mechanisms (4th ed.). Oxford University Press, USA. ISBN 978-0-19-537123-9.
- ^ Usher, Abbott (1988). A history of mechanical inventions (revised, illustrated ed.). Courier Dover Publications. pp. 94. ISBN 978-0-486-25593-4.
External links
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Wikimedia Commons has media related to: Levers |
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Look up lever in Wiktionary, the free dictionary. |
- Lever at Diracdelta science and engineering encyclopedia
- A Simple Lever by Stephen Wolfram, Wolfram Demonstrations Project.
- Levers: Simple Machines at EnchantedLearning.com
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This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
Translations:
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Lever
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
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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