APPLIED MECHANICS LAB.

INSTRUCTION SHEET

SIMPLE SCREW JACK.

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1.  AIM:

       To determine Mechanical Advantage (M.A), Velocity Ratio (V.R), efficiency (h )

and Law of machine of a Simple Screw jack.

 

2.   EQUIPMENT REQUIRED.

2.1 Simple screw jack.

2.2 Weights.

2.3 Vernier caliper                                    

2.4 Rope.

2.5 Effort pan & hanger.

      

3.    DESCRIPTION OF MACHINE.

       Pitch of screw jack (p) =

       Diameter of screw head (D) =

 

 

 

4.    THEORY.

                           Lifting machines are those machines which are used for lifting loads. The effort  is applied at one point of  the machine and the weight is lifted at the other point of the machine. Screw Jack is a device which enables us to lift a heavy load (W)

by applying a comparatively smaller effort (P). 

 

4.1  MECHANICAL ADVANTAGE

The Mechanical Advantage is the ratio of load (W) lifted to effort (P) applied.

                            Thus, M.AÞ W/P

    

4.2    VELOCITY RATIO

       The Velocity Ratio (V.R) is the ratio of the distance moved by effort (y) to the distance moved by load (x).

                          

                             Thus,  V.RÞ y/x

                                                   Þ y/x =  

                                        where,

                                                     D = Díameter of screw head.

           p = Pitch of screw.

4.3   EFFICIENTY(h )

 

                 (h ) = output / input      

               

 

 

 

                          =

 

4.4   LAW OF MACHINE

 

                 It provides the relationship between effort and the corresponding load lifted by the application of effort.

 

                 P = MW + C --------------- (1)

 

    where,    P = Effort applied

                  M = Const. called coefficient of friction which equal to slope of the line.

                  W = Load lifted.

                   C = Const. called machine friction.

 

5        PROCEDURE.

5.3  Measure pitch of screw and dia of screw head then find out V.R.

5.4  Measure machine friction ‘C’ at no load condition.

5.5  Take ten readings taking different loads and efforts.

5.6  Calculate efficiency in each case and calculate mean efficiency.

5.7  Draw the graph between load Vs effort.

5.8  Determine the coefficient of friction ‘M’ from the graph.

5.9  By putting the values of ‘M’and ‘C’ in equation (1) we determine from which the law

      of machine, we can find out the amount of effort required to lift any load.

 

6. OBSERVATION:

 

 

 

Sl no

 

‘C’

Machine friction

‘M’

Coefficient

Of

Machine friction

 

 

V.R

 

 

W

in

(kg)

 

P

in

(kg)

 

Mechanical Advantage

W/P

 

h

(efficiency)

 

Mean

(h )

 

 

 

 

 

 

 

 

 

 

7.  CALCULATION:

 

8.  CONCLUSION: