Experiment No.1 OBJECTIVE : To verify the law of moment by using Bell Crank Lever. APPARATUS : Bell crank lever apparatus, slotted weight, spring balance etc. THEORY : What is a Lever: Lever is a simple machine consisting of a rigid rod pivoted at a fixed point called the fulcrum used for shifting or raising a heavy load or applying force. The lever principle states that Power*power arm = Weight*weight arm. The distance of power applied from the fulcrum is called Power rm and the distance of load !weight" from fulcrum is called weight or load arm. To arrange a lever so that a small effort would lift a big load the effort arm must be as long as possible and the load arm as short as possible. #xamples of lever are $cissors, %heelbarrow, &ore arm, claw hammer to draw a nail, sugar tongs, boat oars, nut crackers ,can openers , bottle openers ,etc. Three classes of levers: First order lever. Like a see-saw or balance, the load and the force are seperated by the fulcrum. As one moves up the orther moves down. The amount and the strength of the movement is proportianal to the distance from the fulcum. eg. $ee $aw, Beam balance, Pair of scissors, etc. Second order lever. wheel barrow is a second order lever. 'ere the load is between the force and the fulcrum. eg. (ut crackers, %heelbarrow , &ishing rods ,etc. Third order lever. Here the force is between the fulcrum and the load. Mechanical advantage is reduced but the movement at the load point is increased. Principle of levers:- The lever principle can be stated as: Load x Length of load arm= Force x Length of force arm Bell Crank Lever: lever that is bent at a right angle, is called a bell crank lever. By varying the angle of the crank piece, it can be used to change the angle or movement from ) degree to )*+ degrees. ,t is one of a type of lever. ,t can be used to change the amount, the strength and the direction of moment. The fixed point of the lever about which it moves is known as the fulcrum. ,t is used to convert the direction of reciprocating moment. By varying the angle of the crank piece it can be used to change the angle of moment from ) degree to )*+ degrees. ccording to law of moments the moment of a force about an axis is e-ual to the sum of moment of its component about the same axis. 'ere in this experiment we have to check the moment of a force about the various point on the lever and that moment must be e-ual to the spring force multiplied by the fixed distance d. The distance d in this experiment is fixed and e-ual to seven inch. $o we have to verify .oment . / % 0 1 / s 0 d %here % / force applied on lever 1 / varying distance on lever $ / spring force nd d / fixed distance ! 203.45/)2.2* mm " PROCEDURE : ). The chain of spring balance was connected with the lever. 3. The weight was hanged on the end point marked on the lever. 6. The pointer was checked to match with the mark on the lever. ! ,f point is not matching then ad7ust the weight to get the correct reading." 5. The spring reading was noted down. 4. The position of weight to be hanged on the lever was changed and the above steps were repeated. 8. Ten readings were taken. OBSERVATIONS: $.(o. % !kg" 1 !mm" ./%01 $pring &orce !observed" !kg&" $ $pring &orce calculated $9/!%01":d ; error ) +.634 6+5.* <<.+8 .8 .44 *.6 3 +.684 32<.5 )+).<* .8 .42 4 6 +.5)4 345.+ )+4.5) .8 .4< ).8 5 +.544 33*.8 )+5.+) .8 .4* 6.6 4 +.4+4 3+6.3 )+3.8) .8 .42 4 8 +.834 )22.* ))).)3 .8 .83 6.6 2 +.324 6+5.* *6.*3 .4 .52 8 * +.634 32<.5 <+.*+4 .4 .4) 3 < +.654 345.+ *2.86 .4 .5< 3 )+ +.6<4 33*.8 <+.3<2 .4 .4+2 ).5 CALCULATIONS: 1istance from fulcrum !d" / 2 inch / 2 = 3.45 cm / +.)22* m. >sing .oment . / %=1 !?g@m" Aalculated $pring &orce !$9" / d D W × !(" ;#rror / )++ B × − S S S RESULT: The observed value of spring force and calculated value of spring force came out to be nearly same. The observed value agrees with the calculated value within the limits of experimental error. CONCLUSION: The law of moments gets verified for this bell@crank lever. SOURCES OF ERROR: ). The success of the experiment lies in making both the spring and lever arm horiContal as well as matching the pointer with the mark on the lever, at exactly the same time. This is possible only if the apparatus is ideal and is free from all arrangement errors. 3. The pointer may not be exactly vertical with respect to ground. 6. The spring pointer may be faulty. 5. $ome friction is always present between the hook of the spring and the chain. 4. The weights are discrete, not variable. $o it is possible that no exact reading may be taken by the given weights. PRECAUTIONS:- ). There should minimal disturbance as long as the pointer is concerned. 3. Dnly one person must take all the readings, because eye@7udgement for matching the pointer with the mark on the lever will vary from individual to individual. 6. %eights should not touch the table. 5. dd weights in the hanger gently. 4. The pointer should exactly coincide with the mark on the bell crank lever. 8. The apparatus should be kept on smooth and leveled surface. 2. Proper lubrication of the 7oints of two arms of the lever should be done so as to reduce frictional force. REFERNCES: • #ngineering .echanics @ by E.?.Ea7put !Ahapter 6" • http:::
[email protected]:mechanisms:pages:lever3.html • http:::en.wikipedia.org:wiki:Lever ! (ote: ccording to railway officials, the $abarmati #xpress accident that took on 3) pril,3++4, could have been caused by the failure of a B#LL AE(? L#F#E GHAlong with the 'human error', railway officials point to a mechanical failure of a bell crank lever — popularly known as the point — on the track.”" @http:::www.mapsofindia.com:maps:mapinnews:3++4:sabarmati@
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