jib crane

EXPERIMENT-6 AIM : To find out forces in the jib member and tie member of the jib crane experimentally and verify it analytically and graphically.

APPARATUS : Jib crane, load hanger, weights and measuring tape.

THEORY : The jib crane is an example of three concurrent forces. The forces in the tie and the jib can be calculated experimentally. Analytically it can be found by making use of Lamis theorem, which states that when three forces acting on a body are in e!uilibrium, then each force is  proportional to the sine of the angle between the other two forces. The apparatus consists of an inclined rod fitted with a compression spring called a jib which is  pivoted and a hook is attached to the other end from which a chain hangs hang s to carry a weight. The vertical tubular rod is fixed at the base and has a sliding adjustable hook. "ne end of the tie rod is fitted to the jib and other o ther end is attached to one of the hooks of tubular rod. A spring spring balance in the tie. The vertical tubular rod is supported for rigidity. The tubular rod is fixed on a heavy base to avoid tilting.

PROCEDURE : #$ %ote the initial reading in the spring balance at the tie member and spring support at the  jib. &$ 'uspend a known weight in the hanger at the apex.

($ )$ $ 0$ 1$

%ote the final readings in the spring balance and spring support. *etermine the effective forces in the jib and tie. +inal reading - initial reading$ /epeat the procedure for different values of the suspended weight. orces in the jib and tie members are found analytically using Lamis theorem. orces in the jib and tie members are found graphically by drawing the space vector  diagram.

OBSERVATION TABLE : S no.

Wt. (kg)

Length o  In%t%&' !e!"e# ($!) #e&%ng (kg)

%n&' #e&%ng (kg)

O"*e#+e #e&%ng (kg)

C&'$,'&te o#$e*

e##o#

AB

AC

BC

%"

t%e

%"

t%e

%"

t%e

%"

t%e

%"

t%e

/

/

00

/10

23

4.5

4.6

/.3

/.6

4.0

/

/.35

/.77

36

74

1

1

00.6

/18

23

4.5

4.6

1.5

1.6

1

1

1.0

1

10

4

7

7

24

/15

23

4.5

4.6

7.5

7.6

7

7

3

1.2

16

7

3

3

24.6

/13

23

4.5

4.6

6

3.6

3.3

3

6

7.0

/.1 6.1

 (&'' %!en*%on* %n $!*)

CALCULATION :

ormulae used, 2n triangle A34 , 56Sinθ2 = P/Sinθ1 = Q/Sinθ3 7 38 LA92:s T;<"/<9=, > ? @ can be calculated.

CONCLUSION : At joint A , 5 is acting downwards. The jib is in co mpression. The tie is in tension.

PRECAUTIONS : The initial readings of balances should be taken into account. The jib and the tie spring balances must be properly oiled for the free mov ement. 9easure the lengths accurately.