# Pressure in Fluids

## •    Thrust is defined as the force acting perpendicular to a surface. The SI unit of thrust is same as the unit of force, i.e., newton (N). The c.g.s. unit of thrust is dyne. •    Pressure is defined as thrust acting per unit area on a surface. The S.I. unit of pressure is pascal (Pa) which is equal to newton per metre square. The c.g.s. unit of pressure is dyne per centimetre square. •    Fluid is defined as any substance that can flow. All liquids and gases are fluids. Fluids also exert pressure due to their weight. Liquids exert pressure not only on the bottom but on the walls of the containers as well. Liquids exert pressure in all directions. •    Pressure exerted by liquids has some definite properties which are known as laws of liquid pressure. Laws of liquid pressure conclude that the pressure exerted by the liquid increases with depth from its free surface and vice-versa. Liquids exert equal pressure in all directions at the same depth. Pressure exerted by liquid at the bottom of the container depends on the height of the liquid column. Liquids exert pressure on the walls of the container.•    Some of the consequences of liquid pressure are walls of dams are made thicker at the base, sea divers wear special kind of diving suits and water tanks are kept at more heights.

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• Q1

The pressure exerted by a liquid of density ‘d’ kgm-3 at the depth of ‘h’ metres from the surface is

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hdg Pa.

##### Explanation:
The pressure exerted by a liquid of density ‘d’ at the depth of ‘h’ from the surface is hdg. When the density is in kgm-3 and the height or depth is in metre, then the unit of pressure is Pascal.
• Q2

Pressure on an object of area 20 cm2 being acted upon by a force of 100 N is

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5 N/cm2.

##### Explanation:

Pressure= Force / Area = 100 N / 20 cm2

= 5 N/cm2
• Q3

Direction of force in pressure is

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perpendicular to the surface.

##### Explanation:
Pressure is defined as the force acting on an object perpendicular to the surface per unit surface area. Therefore, the direction of force in pressure is perpendicular to the surface.
• Q4

The normal force per unit area is called

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pressure

##### Explanation:
Pressure is the normal force per unit area.
• Q5

The force acting on an object perpendicular to the surface is called

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Thrust

##### Explanation:
The force acting on an object perpendicular to the surface is called thrust.