Applications:Pascal’s law for transmission of fluid pressure
- Hydraulic lift is a lift which makes use of a fluid.
- For example: Hydraulic lifts that are used in car service stations to lift the cars.
- Principle: –
- Inside a hydraulic lift there are 2 platforms,one has a smaller area and the other one has a larger area.
- It is a tube like structure which is filled with uniform fluid.
- There are 2 pistons (P1 and P2)which are attached at both the ends of the tube.
- Cross-sectional area of piston P1 is A1 and of piston P2 is A2.
- If we apply force F1 on P1, pressure gets exerted and according to Pascal’s law the pressure gets transmitted in all the directions and same pressure gets exerted on the other end.As a result the Piston P2 moves upwards.
- Advantage of using hydraulic lift is that by applying small force on the small area we are able to generate a larger force.
- Mathematically:- F2=PA2
- where F2 = Resultant Force,A2 = area of cross-section
- F2= (F1/A1)A2 where P=F1/A1 (Pressure P is due to force F1 on the area A1)
- F2 =(A2/A1)F1. This shows that the applied force has increased by A2/A1.
- Because of Pascal’s law the input gets magnified.
The above figure shows the internal structure of the hydraulic lift.
- Hydraulic brakes work on the principle of Pascal’s law.
- According to this law whenever pressure is applied on a fluid it travels uniformly in all the directions.
- Therefore when we apply force on a small piston, pressure gets created which is transmitted through the fluid to a larger piston. As a result of this larger force,uniformbrakingis applied on all four wheels.
- As braking force is generateddue to hydraulic pressure,theyare known as hydraulic brakes.
- Liquids are used instead of gas as liquids are incompressible.
- The fluid in the hydraulic brake is known as brake fluid.
- It consists of a master cylinder, four wheel cylinders and pipes carrying brake fluid from master cylinder to wheel cylinders.
- Master cylinder consists of a piston which is connected to pedal through connecting rod.
- The wheel cylinders consist of two pistons between which fluid is filled.
- Each wheel brake consists of a cylinder brake drum. This drum is mounted on the inner side of wheel. The drum revolves with the wheel.
- Two brake shoes whichare mounted inside the drum remain stationary.
- When we press the brake pedal, piston in the master cylinder forces the brake fluid through a linkage.
- As a result pressure increases and gets transmitted to all the pipes and to all the wheel cylinders according to Pascal’s law.
- Because of this pressure,both the pistons move outand transmit the braking force on all the wheels.
- Equal braking effort to all the four wheels.
- Less rate of wear due to absence of joints.
- By just changing the size of one piston and cylinder, force can be increased or decreased.
- Leakage of brake fluid spoils the brake shoes.
- Even the slightest presence of air pockets can spoil the whole system.