EXPERIMENT

OBJECTIVE:

To determine the velocity ratio, mechanical advantage and efficiency of a single threaded worm and worm wheel.

APPARATUS REQUIRED:

Worm and worm wheel apparatus, weight, string, scale etc.

THEORY:

Worm and worm wheel consists of a square threaded screw (known as worm) and a toothed wheel (known as worm wheel) geared with each other. A wheel is attached to the worm, over which passes a rope a load is securely mounted on the worm wheel.

Let,

R = Radius of the effort wheel

r = Radius of the load drum

W = Load lifted

P = Effort applied to lift the load

T = Number of teeth on the worm wheel

In the first revolution of wheel, distance moved by effort = 2πr, as worm is single threaded.

The load drum will move through  1/T

Distance, through which the load will move = 2πr/T

VELOCITY RATIO (V.R) = Distance moved by effort/Distance moved by load drum

MECHANICAL ADVANTAGE (M.A) = Load/Effort or  W/P

EFFICIENCY = Mechanical Advantage/Velocity Ratio x 100 or M.A/V.R x 100

PROCEDURE:

• Measure the radius of the effort wheel and load drum with the help of string.

• Count the number of teeth on worm wheel.

• Wrap the string over the effort wheel and load drum.

• Suspend some load to the spring passing over the load drum via hanger and go on adding weight in the pan.

• Note the effort in the weight pan.

• Calculate the mechanical advantage and velocity ratio.

• Repeat the experiment with different loads.

OBSERVATION TABLE:

PRECAUTIONS:

• Lubricate the bearings of worm wheel to decrease wheel friction.

• Weight should be gently placed in effort pan.

• String should not overlap on pulley and should not be loose on pulley.

• The pan carrying weight should not be touched.

• There should not be any knot in the string.

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