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Chapter: 11th 12th std standard Class Physics sciense Higher secondary school College Notes

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Applications of Pascal's law: Hydraulic lift and brake

Applications of Pascal's law: Hydraulic lift and brake
An important application of Pascal's law is the hydraulic lift used to lift heavy objects.

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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