SIMPLE LIFTING MACHINE

SIMPLE LIFTING MACHINE

• SIMPLE MACHINE:  - It is a device, which enable to do some useful work at some point or to overcome resistance, when an effort or force is applied to it, at some other point.

Fig.1 | Simple Lifting Machine

• MECHANICAL ADVANTAGE: - It is the ratio of wight lifted (W) to the effort applied (P).

M.A.= W/P

• VELOCITY RATIO: - The ratio of distance move by the effort (x) to the distance moved by the load (y).

V.R.= x/y

• INPUT OF A MACHINE: - Work done on the machine.

For lifting machine I= P.x

• OUTPUT OF A MACHINE: - Work done by the machine.

For lifting machine O = W.y

• EFFICIENCY OF A MACHINE: - It is the ratio of output to the input of a machine.

It is generally expressed in percentage.

η = Output / Input.

= W.y / P.x

= (W /P) / (x / y)

= MA / VR

• IDEAL MACHINE:  - If the efficiency of the machine is 100% i.e. output is equal to input, then the machine is called perfect or ideal machine.

• REVERSIBLE MACHINE:  - If a machine is capable of doing some work in the reversed direction, after the effort is removed, then the machine is known as reversible machine.

Condition - Efficiency should be more than 50%.

Here, Output > Frictional losses

W.y > (Px - Wy)

2Wy > Px

(Wy/Px) > 1/2

MA/VR > 1/2

η > 1/2

η > 50%

• NON-REVERSIBLE / IRREVERSIBLE / SELF LOCKING MACHINE:  - If a machine is not capable of doing work in the reversed direction, after removal of the effort, then the machine is known as irreversible machine.

Here frictional resistance is more than work done by the load in reverse direction.

η ≤ 50%

• LAWS OF THE MACHINE:  - It is the relationship between the load lifted (W) and the effort applied (P).

Fig.2 | Law of Simple machine

It is given by the equation P = m.W + C

Where m = A constant, called co-efficient of friction. (Which is equal to the slope of the line AB)

C = Another constant which represents the machine friction.

• Maximum mechanical advantage of a lifting machine:  - Max MA = 1/m
• Maximum efficiency of a lifting machine:  - Max η = 1/ (m x V.R.)

• SYSTEM OF PULLEY: -

Max η = 1/ (m x V.R.)

1. First system of pulley: -

Fig.3 | First System of Pulley

n = No. of pulley in the system.

2. Second system of pulley: -

Fig.4 | Second System of Pulley

3. Third system of pulley: -

Fig. 5 | Third System of Pulley