PRESSURE
Pressure :- The effect of force over a unit area is called pressure.
-Thrust or normal force :- The force that acts normally (perpendicular) over a surface is called trust or normal force.
* S.I. unit of pressure is Pascal (Pa).
* Pressure = Force/ Area.
• Pressure is directly proportional to the force.
- Pressure (increase) force will also (increase).
- Pressure (decrease) force will also (decrease).
• Pressure inversely proportional to the area.
- Area (increase) pressure will (decrease).
- Area (decrease) pressure will (increase).
1Pa = 1N/1m2 = 1N/m2= 1Nm2
When 1N of force acts perpendicular to the surface of unit area than the pressure is said to be 1 pascal.
- Another unit of pressure is bar, atm, etc.
• 1bar = (10)5 pascal.
RELATION BETWEEN AREA AND PRESSURE:-
SbRELATIONSHIP BETWEEN AREA A
• Area is less than pressure is greater between paper and pencil.
So, the tip of pencil easily pierce the paper.
• The area is more than the pressure is lesser between paper and the end of pencil.
So, the ends of pencil cannot pierce easily to the paper.
• It is more comfortable to wear broad heels while walking on soft surface.
• Elephants and bears have broad feet to help them walk on soft surfaces without falling.
• The width of straps of bags and suitcases is increased to reduce pressure while carrying them.
RELATION BETWEEN FORCE AND PRESSURE :-
• For the same area, when the force applied increases, the pressure increases.
• When the forces decreases, the pressure decreases.
PRESSURE EXERTED BY LIQUIDS :-
• The pressure exerted by liquid depends upon the depth of the water column.
• They exert pressure not only at the base of the container but also on its sides.
Liquid pressure varies with depth:-
• Water from the lowest hole comes out with the greatest force and falls at the maximum distance.
• Water from the topmost hole comes out with the least force and falls at the minimum distance.
* An instrument used to measure liquid pressure is called pressure gauge. The simplest form of a pressure guage is a manometer.
ATMOSPHERIC PRESSURE
- The pressure exerted by the weight of the air on an object is called atmospheric pressure.
• ALTITUDE :- The height of a place above the sea level is known as altitude.
* The scientific instrument used in meteorology to measure atmospher pressure is Barometer.
Atmospheric pressure decreases with altitude
The height and weight of the air column decreases as we go up. Therefore, the atmospheric pressure also reduces as we go to higher places. Hence, the atmospheric pressure at a place depends on its altitude.
FORCE OF ATMOSPHERIC PRESSURE
• The pressure exerted by atmosphere is very large. This was demonstrated by a German physicist and engineer, Otto von Guericke. He took two semicircular copper bowls and fitted them together to form a sphere. Then he sucked all the air from the sphere using a suction pump to create a vaccum inside the sphere. The two bowls were now held together only due to the atmospheric pressure. Then he tried to separate the two bowls by getting them pulled apart by a team of eight horses on each side. The bowls remained held tightly together due to the atmospheric pressure and did not separate. This proved the enormous force of atmospheric pressure.
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