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ELEMENTS OF TECHNOLOGY(LEVERS)

BY

RAGHAVEE GOELDEEPANSHUHARSHDEEP SINGH

ADITI CHAKRABORTY

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WHAT IS A LEVER? In physics, a lever(from French lever, "to raise")is a rigid object that is used with an appropriatefulcrum or pivot point to either multiply themechanical force (effort) that can be applied to

another object or resistance force (load), ormultiply the distance and speed at which theopposite end of the rigid object travels.This leverageis also termed mechanicaladvantage, and is one example of the principle of

moments. A lever is one of the six simplemachines.

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HOW DOES IT EASE

OUR WORK? A lever is a simple machine that makes work

easier for use; it involves moving a loadaround a pivot using a force. Many of ourbasic tools use levers, including scissors (2class 1 levers), pliers (2 class 1 levers),hammer claws (a single class 2 lever), nut

crackers (2 class 2 levers), and tongs (2class 3 levers).

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EXAMPLES OF LEVERS see-saw

hammer's claws

Scissors fishing rod

tweezers

tongs

pliers

stapler

bottle opener wheelbarrow

nail clippers

nut cracker

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PRINCIPLE OF

MOMENTS If a body is in equilibrium under the action

of a number of forces, then the algebraicsum of the moments of the forces aboutany point is equal to zero.

In other words, the sum of the clockwisemoments equals sum of the anticlockwise

moments when the body is in equilibrium.

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Contd.Sum of the anticlockwise moments = Sum

of the clockwise moments i.e., (50 x 40) +(100 x 20) + (60 x 10) = (30 x 20) + (100 x40)

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CLASSES OF LEVERS There are three classes of levers representing variations inthe relative locations of the fulcrum, the load and theforce:-

Class 1: The fulcrum is located between the applied forceand the load, for example, a crowbaror a pair of scissorsora seesaw.

Class 2: The load is situated between the fulcrum and theforce, for example, a wheelbarrowor a nutcracker.

Class 3: The force is applied betweenthe fulcrum and theload, forexample, a pair of tweezersor the humanmandible.

http://en.wikipedia.org/wiki/Crowbar_(tool)http://en.wikipedia.org/wiki/Scissorshttp://en.wikipedia.org/wiki/Seesawhttp://en.wikipedia.org/wiki/Crowbar_(tool)http://en.wikipedia.org/wiki/Scissorshttp://en.wikipedia.org/wiki/Seesawhttp://en.wikipedia.org/wiki/Wheelbarrowhttp://en.wikipedia.org/wiki/Nutcrackerhttp://en.wikipedia.org/wiki/Wheelbarrowhttp://en.wikipedia.org/wiki/Nutcrackerhttp://en.wikipedia.org/wiki/Tweezershttp://en.wikipedia.org/wiki/Human_mandiblehttp://en.wikipedia.org/wiki/Human_mandiblehttp://en.wikipedia.org/wiki/Tweezershttp://en.wikipedia.org/wiki/Human_mandiblehttp://en.wikipedia.org/wiki/Human_mandiblehttp://en.wikipedia.org/wiki/Human_mandiblehttp://en.wikipedia.org/wiki/Human_mandiblehttp://en.wikipedia.org/wiki/Tweezershttp://en.wikipedia.org/wiki/Nutcrackerhttp://en.wikipedia.org/wiki/Wheelbarrowhttp://en.wikipedia.org/wiki/Seesawhttp://en.wikipedia.org/wiki/Scissorshttp://en.wikipedia.org/wiki/Crowbar_(tool)

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1ST

CLASS LEVER axis is placed between force and resistance

examples: crowbar, seesaw, scissors

examples in body:

elbow extension

tricepsapplying force to olecranon (F) inextending the non-supported forearm (R) atthe elbow (A)

flexing muscle

agonist (F) and antagonist (R) muscle groupsare simultaneously contracting on either sideof a joint axis (A).

http://www.exrx.net/Articulations/Elbow.htmlhttp://www.exrx.net/Muscles/TricepsBrachii.htmlhttp://www.exrx.net/Muscles/TricepsBrachii.htmlhttp://www.exrx.net/Articulations/Elbow.html

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Contd. lever characteristics

balanced movement

axis is midway between force and resistance e.g.: seesaw

speed and range of motion axis is close to force

e.g.: elbow extension

force axis is close to resistance

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Contd. Diagramatic representation of 1st

class lever.

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2nd CLASS LEVER Resistance is between axis and force

classic examples: wheelbarrow, nutcracker

complex example: rowing

paddle in water acts as slipping axis (A)

boat resistance is resistive force (R)

rower is motive force (F)

relatively few examples in body planter flexion of foot to raise body up on toes

ball of foot (A) serves fulcrum as ankleplantar flexors apply force to calcaneus (F) to

lift resistance of body at tibial articulation(R) with foot.

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Contd. entire body during push-up

foot is axis of rotation (A) when reaction force ofground pushing against hands (F) lifts weight ofbody's center of gravity (R).

lever characteristics

produces force: large resistance can be moved by arelatively small force

weight machines: more resistance needed, lower inertia,smoother feel

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Contd. Examples

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3RD

CLASS LEVER force is placed between the axis and resistance

examples:

tongs: food (R) is supported by grip on handles

(F) while axis is on opposite end. shovelling: dirt on shovel (R) is lifted by force

to handle by hand (F) while upper hand on endof shovel handle serves as axis (A)

rowing: oar is moved through water (R) bypulling on middle of oar (F) while holding end ofoar with opposite hand (A).

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Contd. Note: shovelling and rowing actions can also

be first class lever systems if the handcloses to the force remains stationary (A)and the hand on the far end of the shovel oroar is moved (F).

batting: ball is hit (R) by moving bat toward ball

with hand of far arm (F) while supporting lowerportion of bat with hand of near arm (A).

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Contd. Examples