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PRESSURE

KEY WORDS

words meaning

Pressure The force acting per unit area of the surface.

Pascal SI unit of pressure.

Thrust Total force acting vertically on the surface of a body.

FluidThe substance which can flow.

Manometer A simple device used to measure liquid pressure.

Atmospheric pressure The pressure exerted by the layer of air around the earth

barometer The apparatus used for measuring the air pressure

INTRODUCTION Effect of force on a given area is called

pressure. Pressure depends on two factors. They are:

force applied and area over which force acts. The formula of pressure is:

Pressure=Force/Area. Pressure can also be defined in terms of

another force called thrust. The force acting on a body perpendicular to

its surface is called thrust. So, we can also define pressure as thrust per

unit area is Pressure=Thrust/Area. The SI unit of pressure is Pascal (Pa).

EXAMPLES OF PRESSURE It is easier to cut an apple from the

sharper side than blunt because the sharper side has less area.

Porters wear turbans while carrying heavy loads on heads. By doing this pressure on their heads gets reduced due to the increase in area of contact.

Wooden sleepers are kept below the railway lines so that there is less pressure of the train on the ground and railway lines do not sink into the ground.

FLUID PRESSURE Unlike solids, the liquids do not have a definite

shape. They take the shape of the containing vessels.

The pressure in liquids is not thrust per unit area. instead it depends it depends upon the depth and density of the liquid.

Fluids have weight so they exert pressure on the base and walls of the container.

The pressure at a depth in a liquid depends upon two factors:

1) The height of the liquid column.2) The density of the liquid.

THE MANOMETER A manometer is a simple device

used to measure liquid pressure. It has a U – shaped tube which is

fixed to a wooden board having a scale.

The U – tube is filled with coloured water such that its limbs are half filled.

One end of the U – tube is open, the other end is fixed to a rubber tube which in turn is connected to a thistle funnel .

This improvised apparatus is called as manometer .

CONSEQUENCES OF LIQUID PRESSURE

The pressure exerted by water in the oceans increases with depth.

When deep sea fishes are brought up to the surface of the sea, their body flow at a Very high pressure.

ATMOSPHERIC PRESSURE

Like all gases, air also have weight hence exerts pressure.

The force exerted by the atmosphere on unit area is called atmospheric pressure.

Air exerts huge pressure in every direction.

THE BAROMETER A barometer is an instrument used to measure

atmospheric pressure. It consists of long and thin tube filled with

mercury and closed at one end. The open end of the tube is placed in a small

trough full of mercury. The pressure exerted by air on the mercury of

trough is able to hold certain height of the mercury column.

When the air pressure is low, the mercury will move down.

When the air pressure increases, the height of the mercury column increases

APPLICATIONS OF PRESSURE

The edge of the knife is made sharper increase pressure.

The sole of sport shoes have spikes have spikes to increase the grip through pressure.

In vacuum cleaner a low pressure is created inside with the help of a fan and this low pressure helps in the working of vacuum cleaner.

The straw helps us to drink juice because the atmospheric pressure is exerted on the surface of the juice.

FACTS The pointed end of a high heeled shoe

exerts more pressure than what an elephant’s flat exerts.

It is due to the upward force exerted by water that we are able to swim.

The pressure of water vapours in a streaming pressure cooker, cooks the food faster.

The first mercury barometer was made by an Italian scientist terriceilliinm 1643.

submarines are built of hard thick sheets of metal to withstand the high pressure of water.

LET US REVISE The effect of force on a given area is called

pressure. The SI unit of pressure is Pascal(Pa)equal to

1 Newton per meter square the pressure exerted by air is called atmospheric pressure.

Atmospheric pressure is measured with barometer.

A liquid exerts pressure in all direction. At the same depth the pressure is same in

all direction. Liquid pressure increases with depth. Liquid pressure is measured with

manometer.