Pascal's Principle

Pascal principle states that:
Pressure applied in a confined liquid is transmitted uniformly in all direction through out the liquid.

Experiment to verify the Pascal’s Principle

When the piston is pushed into the glass sphere the jet of water is shot out from the holes in the glass sphere with the same speed.

This is because the pressure acting on the water is transferred uniformly throughout  the water.

Pascal’s Principle in Mathematic Expression

Output force = output piston area

Input force      input piston area

        

  F₂      = A₂

        F₁         A₁

Applications of Pascal’s Principle

(1)Automobile hydraulic lift

Automobile hydraulic lift is used to lift a vehicle in a workshop.

The system uses Pascal’s Principle to produce a larger force to lift a heavy vehicle.

When incompressible fluid is moved through a hydraulic system, the volume through which the input system moved must be the same as the volume through which the output system,

Hence

                                A₁d₁  =  A₂d₂

Based on the Pascal’s Principle,the pressure is transmitted throughout all points in the fluid and acts in all directions,

                                F₁  =  F₂

                                A₁       A₂  

Determine

(a)    The pressure  transmitted in the hydraulic fluid.

(b)    The mass of the load.

(c)     If  the small piston is pushed down  at  a depth a 0.04 m, what is the distance moved by the large piston.

(2) Hydraulic Jack

When the handle is pulled, valve P is still closed and valve Q opens so the pressure can be sent to the larger piston. The large piston will rise.

While the small piston is pulled out, valve Q closes and valve P opens so that  the oil in the tank enter into the hydraulic cylinder as a result of atmospheric pressure.

By moving the push-pull handle a number of times , the large piston can be raised carrying a heavy load.

(3)  Hydraulic Brake

A small force acting at the pedal can transmit a large force to all wheels simultaneously to stop the car.

It is because the  pressure will be transferred through the pedal brake liquid to car’s tyre .

• When the brake pedal is pressed, the piston of the master cylinder applies a pressure on the brake fluid.
• This pressure is transmitted uniformly to each cylinders at the wheel, cause the pistons at the wheels to push the brake shoes to press against the surface of the brake.
• The friction between the brakes and brake shoes causes the vehicle to slow down and stop.