Pressure can be defined as a continuous physical force exerted on or against an object by something in contact with it. Thrust is the force acting perpendicularly on any area.

The uses of pressure are various as:

• Syringes are used to take blood for blood tests. The pressure of the liquid (blood) forces the liquid to move into the syringe when its plunger is withdrawn.
• When air is sucked out of a drinking straw, the air pressure inside if decreases and the atmospheric pressure outside forces the liquid to go inside the straw.
• Skis have a large area to reduce the pressure on the snow. This ensures that the skis do not sink into the snow too far.

Unit of thrust = Newton(N)

Pressure(P)= Thrust(f)/Area(A)

Unit of pressure = {Newton(N)/ meter²(m²)} Pascal

                                = Nm^-2

                                = dyne/cm²

Other units of pressure are barometric pressure

• Mm Hg (1 torr) (ii) cm Hg (iii) m Hg

1 atmospheric pressure = 0.76 m of hg column

The calculation of pressure is = Pressure(P)= {(Area*height) density of liquid*Acceleration due to gravity}/Area

= (A*h) d*g/A

=h*d*g

Height of Hg column to measure atmospheric pressure in standard condition = 76 cm of hg 

P=hdg

= 0.76*13.6*10³*10 Nm^-2

Acceleration due to gravity = 9.8ms^-2

What height of water will be required to measure atmospheric pressure instead of hg

ANS- H * D_(water) * G = 0.76*13.6*10³

              ⁼ H*D_(water)= 0.76*13.6*10³

         = H*1000= 0.76*13.6 * 10³               (Density of water = 1000 kg m-3)

          = H= 10.336

                        Water                                               30 cm

                          Hg                                               20 cm

                  P                                                                

Calculate pressure at P

P= H*d*g

P= (0.3*1000*10) + (0.2*13.6*10³*10)

  = (0.3+0.2+13.6) *10³*10

  = (0.3+2.72) *10³

 = 3.02*10³ * 10 Pa