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LESSON NOTES

Thrust and Pressure
Thrust: Force exerted by an object perpendicular to the surface is called thrust.

Pressure: Pressure is defined as thrust or force per unit area on a surface.
 Pressure = Thrust/Area
2
2
 SI unit of pressure is Newton/meter (N/m ).
 SI unit of pressure is called Pascal (Pa).
Factors affecting Pressure

Pressure depends on two factors:

(i) Force applied
(ii) Area of surface over which force acts

Since, pressure is indirectly proportional to the surface area of the object, so, pressure
increases with a decrease in surface area and decreases with an increase in surface

area.

Applications of Pressure in daily life
 The base of high buildings is made wider to spread the weight of the whole building

over a large surface area due to which less pressure acts on the ground.
 School bags are provided with broad straps so that the weight of school bags falls over

a larger area of the shoulder and produce less pressure hence making it easy to carry.
 The blades of knives are made sharp so that on applying force on it, a large pressure is

produced on the very small surface area, thus cutting the object easily.
Pressure in Fluids

 Anything that can flow is called Fluid. Example: liquid and gas.
 Molecules of a fluid move randomly and collide with walls of vessel. Thus fluids apply
pressure on walls.

 Fluids exert pressure in all directions.
 The pressure exerted by a static fluid or hydrostatic pressure, is the pressure in

an equilibrium system that depends only upon the depth of the fluid, the density
of the fluid, and the acceleration of gravity. Its units are the same as pressure in
2
general, N/m . The formula for pressure in a fluid is given: