Page 181 - WCS - Electrical

WORKSHOP CALCULATION & SCIENCE - CITS

The lever consists of a rigid rod, which can turn freely about a fixed point, known as fulcrum. The perpendicular
distance from the fuicrum to the lines of action of the effort and the load are called the arms of lever. Effort
arm means perpendicular distance from the fulcrum to the lines of action of effort. Similarly, load arm means
perpendicular distance from the fulcrum to the lines of action of load. Levers are classified into two categories:
(1) Straight levers (ii) Curved levers
Whatever the category of levers it may be, it works on the following principle:
Load x Load arm = Effort x Effort arm

This principle is known as principle of levers.
1 Straight Levers:They are classified into three orders i.e., first, second and third order(i.e.,F.L.E. of levers)
(1) First Order [Fig. (a)]
In first order, the fulcrum is in between effort and load.

Examples : Beams of a common balance, sea-saw.
: Handle of a tube well pump, crow bar.
: Claw hammer, A pain of pliers.
: A pair of scissors, Hand pump.
(2) Second Order [Fig. (b)]

In second, load is in between fulcrum and effort.
Example : A wheel barrow, paper sheet cutter,
: A nut cracker, lemon squeezer.
: A pinch bar used to turn a load
: Oar of a boat, Bottle openers.

(iii) Third Order [Fig. (c)]
In third order, effort is between load and fulcrum.
Examples: Coal tongs, forceps, broom,
: Human forearm, fishing rod,
: A safety valve lever etc.

Curved Levers because of its name, a lever which is bent, is known as curved lever. In this type of levers, both the
arms are bent between 0° to 180°. Best example of curved lever is Bell cranked lever, in which arms are usually
bent at 90° and motor cycle breaks system, clutch pedal.
Application of Levers
Levers of different order are combined together in machines. For example, combination of first and second order
is used in typewriter Combination of different order of levers is also found in applying brakes to motor byke, cycle
and also found in instruments like a neroid barometer etc.
Examples

1 According to figure the lever has to support a 100 kg load with a 17 kg equivalent force supplied to it. Find the
distance between the load and point of force.
Solution: Load = 100 kg; Effort = 17 kg
Load arm = 50 cm

Let effort arm = x cm
As per principle of levers:
Effort x Effort arm = Load x Load arm

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CITS : WCS - Electrical - Exercise 17