PRESSURE

CHAPTER-12

PRESSURE 

(^2 stand for "raised to the power 2" or squared)

The extent of effect that a force produces on an object is called pressure.It depends on two factors-

• The amount of force applied-The greater the force,the greater is its effect.
• The area over which the force is applied i.e the area of contact between two objects ,the smaller the area the greater is its effect.

Pressure is also defined as force per unit area.Pressure = Force/Area.

The S.I unit of pressure is newton per square metre. The unit of pressure is commonly known as pascal (Pa) after the french scientist Blaise Pascal. Pressure can also be measured in kg wt/m^2. In the CGS system,the unit of pressure is dyne/cm^2.

We can also define pressure in terms of Thurst.In fact,thurst is the total force acting on the surface of an object. So thurst per unit area is called pressure.Thus pressure=Thurst/Area..The S.I unit of thurst is also Newton.

NUMERICALS

Consider the following examples

1.A force of 2N is applied over an area of 4cm^2.Calculate the pressure.

Answer-To get pressure in Pa or N/m^2 ,We have to make sure that the force is in newton and the area in m^2.Here the force is in Newton but the area is in cm^2.To convert this we need to divide the given area by 10.000.

Thus area = 4/10000=0.0004 m^2.

Now,pressure =force/area= 2N/0.0004 m^2 = 5000N/m^2.

Now try solving the following examples-

1.A force of 12N is applied over a area of 4 cm^2.Calculate the pressure.

2.A force of 2N is applied over a area of 2 cm^2.Calculate the pressure.

*In all of the above examples you will find that the greater the force, the greater is the pressure.

*The smaller the area ,the greater the pressure exerted.

LIQUID PRESSURE

Liquid exert pressure equally in all directions.The pressure exerted by the liquids is called liquid pressure.Liquids have weight hence they exert downward pressure on the bottom.Liquids also exert pressure upward.The upward pressure exerted by a liquid is also called thurst.Upward thurst from water helps swimmer and aquatic animals in keeping them afloat on water .Liquid pressure varies with depth .It increases with depth.

The pressure at any point of liquid depends on; 

• The depth of liquid at that point.The greater the depth the more is the pressure.
• The density of the liquid.The greater is the density,the greater will be the pressure at any level.
• The pull of gravity.

Thus the pressure can be calculated by using the formula

                                                         P=hdg

Where P is the pressure in N/m^2, h is the depth of liquid in metre, d is the density of liquid in kg/m^3 and g is the gravity due to earth in N/kg which is almost equal to 10N/kg or 9.8N/kg.

Liquid pressure is measured in a instrument called manometer.

**THE CONCEPT OF "ATMOSPHERIC PRESSURE" WOULD BE UPLOADED  IN MY NEXT POST.

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