EXPERIMENT-4 OBJECTIVE To To verify the the Law of Moments by by using a Bell Bell Crank Lever. Lever.
APPARATUSBell crank lever apparatus, slotted weights, spring balance and pointer.
THEORY-
A bell crank is is a type of crank that changes motion through an angle. The name comes from its rst use, changing the vertical pull on a rope to a hori!ontal pull on the striker of a bell, used for calling servants in upper class British households. The "ed point of the lever about which it moves is known as the fulcrum. The bell crank crank consists of an #L# shaped crank crank pivoted where where the two two arms of the the L meet. Moving rods $or ropes% are attached to the ends of the L arms. &hen one is pulled, the L rotates around the pivot point, pulling on the other arm.
Changing the length of the arms changes the mechanical advantage of the system. Many applications do not change the direction of motion, but instead to amplify a force #in line#, which a bell crank can do in a limited space. There is a tradeo' between range of motion, linearity of motion, and si!e. The greater the angle traversed by the crank, the more non(linear the motion becomes $the more the motion ratio changes%. According to law of moments When an object is balanced (in equilibrium) the sum of the clockwise moments
is equal to the sum of the anticlockwise
moments.
Applications Aircraft Bellcranks are often used in aircraft control systems to connect the pilot)s controls to the control surfaces. *or e"ample+ on light aircraft, the rudder often has a bellcrank whose pivot point is the rudder hinge. A cable connects the pilot)s rudder pedal to one side of the bellcrank. &hen the pilot pushes on the rudder pedal, the rudder rotates on its hinge. The opposite rudder pedal is connected to the other end of the bellcrank to rotate the rudder in the opposite direction.
Automotive
Bellcranks are also seen in automotive applications, as part of the linkage connecting the throttle pedal to the carburetor, and connecting the brake pedal to the master brake cylinder. n vehicle suspensions, bellcranks are used in pushrod( style suspensions in automobiles or in the Christie suspension in tanks. -ertically( mounted suspensions may not be feasible in some vehicle designs due to space, aerodynamic, or other design constraints bellcranks translate the vertical motion of the wheel in to hori!ontal motion, allowing the suspension to be mounted transversely or longitudinally within the vehicle.
/ere in this e"periment we have to check the moment of a force about the various point on the lever and that moment must be e0ual to the spring force multiplied by the "ed distance d. The distance d in this e"periment is "ed and e0ual to seven inch. 1o we have to verify
Moment, M 2 & 3 4 2 s 3 d
&here & 2 force applied on lever 4 2 varying distance on lever 1 2 spring force
And d 2 "ed distance $536.78295.5: mm%
PROCEDURE9% 6% <% 8% 7% ?%
;ngage the chain of spring balance with the lever. /ang the weight on the end point marked on the lever. Check the pointer to match with the mark made on the lever. f the pointer does not match, ad=ust the weights to get the readings. >ote down the spring readings. Change the position of weight to be hanged on the lever @ repeat the above steps. 5% Take at least si" readings.
OBSERVATIONSS.n
!e"#
%$D"&%ance
M'en%
! k#
D "nc$e&
M(!)D
S*r"n# +rce S,k#
Calcla% e/ 0ale + S
3errr ,S1S2S1
S1(!D2 /
X 1
1
9.7
?
9
9.6:
69.:
5
6
8
:
9
9.95
95.6
6
.57
99
:.67
9
9.9?
98.7
4
9
5
5
9
9
6
CA7CU7ATIONS4istance from fulcrum $d% 2 5 inch sing Moment M 2 &D4 $Eg(inch% W × D d
Calculated 1pring *orce $1F% 2
$>%
S '− S S '
×100
G;rror 2
RESU7T*rom the values obtained above, itFs clear that the observed and calculated values obtained for the value of spring force are nearly e0ual and within the permissible e"perimental error limits. /ence the Law of Moments has been veried
PRECAUTIONS9. There should minimal disturbance as long as the pointer is concerned. 6. Hnly one person must take all the readings, because eye(=udgement for matching the pointer with the mark on the lever will vary from individual to individual. <. &eights should not touch the table. 8. Add weights in the hanger gently. 7. The pointer should e"actly coincide with the mark on the bell crank lever. ?. The optimum starching of spring should be kept in mind. 5. The apparatus should be kept on smooth and leveled surface. :. Iroper lubrication of the =oints of two arms of the lever should be done so as to reduce frictional force. . Jero error of spring should be properly noted.
