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EDUCATIONAL STUFFS

An Ocean of Information

April 22, 2021February 14, 2025

APPLIED MECHANICS- Jib Crane Practical

EXPERIMENT

 

OBJECTIVE:

To Verify Lami’s theorem by finding the forces in the different members of a Jib-crane.

 

APPARATUS REQUIRED:

Jib Apparatus, Weight, Meter Rod, Set Square, Pencil etc.

 

THEORY:

jib crane

 

Lami’s Theorem states that If three coplanar concurrent forces are acting on a body and keeps the body in Equilibrium, then each force is proportional to the sine of the angle between the other two forces.

 

jib crane

 

PROCEDURE:

  • Take the initial reading of forces in the compression spring balance of rod and tension spring balance of the tie rod.
  • Suspend a known weight ‘w’ with the help of weight hanger.
  • Take final reading of force in jib rod and tie rod of spring balance.
  • From the final reading subtract the initial reading to get observed value of the forces in rod and tie rod.
  • Measure the length of jib rod from the point on the platform, the position where string is attached, length of the tie rod and vertical height of the post.
  • From the above measurement, draw the space diagram to a suitable scale and name the member by bow’s notation.
  • Measure the internal angles contained between the two forces in vector diagram.
  • Measure angle α, β and γ and apply Lami’s theorem to find out the forces in the member e.g.

[frac up=”W” down=”sin α”] = [frac up=”P” down=”sin β”] = [frac up=”R” down=”sin γ”]

  • Equating 1st and 2nd, we get,

[frac up=”W” down=”sin α”] = [frac up=”P” down=”sin β”]  or  P = [frac up=”(W . sin β )” down=”sin α”]

  • Similarly, equating 2nd and 3rd, we get,

[frac up=”P” down=”sin β”] = [frac up=”R” down=”sin γ”] or R = [frac up=”(P . sin γ)” down=”sin β”]

  • Compare the calculated values of forces with observed values and determine the percentage error.
  • Repeat the experiment either by changing the load or by varying the length of the vertical post.

 

 

OBSERVATION TABLE:

S. No. Weight on post (W in kg) Length of members of jib crane (in cm) Initial Reading (I) (in kg) Final Reading (F) (in kg) Observed Value (F-I) (in kg) Calculated Force (in kg) Percentage Error of Force
(in percentage)
JIB TIE POST JIB TIE JIB TIE JIB TIE JIB TIE JIB
[frac up=”(P1 – P)” down=”P1″] x 100
TIE
[frac up=”(R1 – R)” down=”R1″] x 100

 

 

PRECAUTIONS:

  • Initial reading of the spring balance of tie rod and jib rod should be taken carefully.
  • Weight should be suspended gently without any jerk.
  • Measure the length of each member of jib crane with an extensible string.
  • The spring balance  should be sensitive to give correct reading.
  • The space and force diagram should be drawn correctly.

 

 

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