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Title: Screw Jack
Aim:
1.
To obtain the velocity ratio of the machine.
2.
To plot graphs on a base of increasing load,
illustrating the variation of
a)
Effort
b)
Effect on Friction
c)
Efficiency
3.
To obtain an equation for the relation
between load and effort, and hence obtain a value for the limiting efficiency
of machine.
Apparatus:
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THEORY:
The
Screw Jack is a device used for lifting heavy loads which are usually centrally
loaded by applying smaller effort. It works on the principle of inclined plane.
The device consists of a nut and screw. The load is carried by screw head. The
body consisting of a nut is fixed and screw is
rotated
by means of a lever.
The
axial distance moved by the screw when it makes one complete revolution is
known
as the Lead of the screw. The distance between two consecutive threads is
called Pitch
of
the screw.
For
single threaded screw Lead = Pitch, and for double threaded screw L = 2p
Mechanical Advantage:
It
is the ratio of weight lifted to effort applied.
M.A.
= W/ P
Velocity Ratio:
It
is the ratio of distance moved by the effort (y) to the distance moved by the
load (x).
V.R.
= y/ x
In
one complete revolution of the lever by effort P:
Distance
traveled by effort = 2 π R
And,
distance traveled by the load = p
Therefore, Velocity Ratio =
2 π R / p
For Procedures, See your Mechanical Laboratory Manual.
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Observations :-
1.
Applications:-
PRECAUTIONS:
For
Precautions, See General Laboratory Precautions
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