PRESSURE

Pressure is defined as

“The perpendicular force acting per unit area of a surface."

Mathematically:

Pressure = Force / Area

P = F / A

Units of pressure: -

(i) N/m2 or Pascal       (IN S.I. system)

(ii) Atmosphere

(iii) cm of Hg

(iv) mm of Hg or Torr

PRESSURE IN LIQUIDS: -

The pressure at any point in a liquid depends on the density and the depth in the liquid.

EXPLANATION: -

Consider a liquid of density “r “.

We know that:

Density = mass / volume

ρ = m / V

But area x height = volume i.e. A x h = V

ρ = m / Ah

or

m = ρ A h

Since W = mg, therefore

W = ρ A h g

Also

P = F / A ---------------- (i)

Force applied is equal to the weight of the liquid i.e.

F = W = ρ A h g

Putting the value of F in equation (i), we get

P = ρ A h g / A

P = ρ h g

This is the required expression for pressure in liquids.

PASCAL'S LAW: -

STATEMENT: -

Pascal's law states that:

“Liquids transmit pressure equally in all directions."

In other words

"When pressure on any portion of a confined liquid is changed, the pressure on every other part of the liquid is also changed by the same amount."

It has been observed that if we apply pressure to a liquid in a container, then it is transmitted equally in all direction & acts perpendicularly to the walls of the container.

USES OF PASCAL'S LAW: -

Pascal's Law has a number of applications in our daily such as:

·         Hydraulic Brakes

·         Hydraulic Press

·          Hydraulic Lift