Applications of Pascal's law
(i) Hydraulic lift
An important application of Pascal's law is the hydraulic lift used
to lift heavy objects. A schematic diagram of a hydraulic lift is shown in the
Fig.. It consists of a liquid container which has pistons fitted into the small
and large opening cylinders. If a1
and a2 are the areas of
the pistons A and B respectively, F
is the force applied on A and W is
the load on B, then
F/ a1 = W/a1
W = Fa2/a1
This is the load that can be
lifted by applying a force F on A. In the above equation 2 a1/a2
is called mechanical advantage of
the hydraulic lift. One can see such a lift in many automobile service stations
(ii) Hydraulic brake
When brakes are applied suddenly in a moving
vehicle, there is every chance of the vehicle to skid because the wheels are
not retarded uniformly. In order to avoid this danger of skidding when the
brakes are applied, the brake mechanism must be such that each wheel is equally
and simultaneously retarded. A hydraulic brake serves this purpose. It works on
the principle of Pascal's law.
Fig. shows the schematic
diagram of a hydraulic brake system. The brake system has a main cylinder
filled with brake oil. The main cylinder is provided with a piston P which is
connected to the brake pedal through a lever assembly. A T shaped tube is provided at the other end of the main cylinder.
The wheel cylinder having two pistons P1 and P2 is
connected to the T tube. The pistons
P1 and P2 are connected to the brake shoes S1
and S2 respectively.
When the brake pedal is pressed, piston P is
pushed due to the lever assembly operation. The pressure in the main cylinder
is transmitted to P1 and P2. The pistons P1
and P2 push the brake shoes away, which in turn press against the
inner rim of the wheel. Thus the motion of the wheel is arrested. The area of
the pistons P1 and P2 is greater than that of P.
Therefore a small force applied to the brake pedal produces a large thrust on
the wheel rim.
The main cylinder is connected to all the
wheels of the automobile through pipe line for applying equal pressure to all
the wheels .
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