Concepts

Class 9
Chapter 1 Class 9 - Matter In Our Surroundings

## Pressure

Pressure may be defined as the physical force applied on an object.

The particles of matter come closer t o each other when pressure is applied

When pressure is applied on gas enclosed in a cylinder, it is converted to liquid (as the particles come closer)

However it is difficult to apply pressure on liquid and solids.

• The space between the particles in solids and liquids is already very less
• Applying pressure will not bring the particles closer and so will not bring a change in state of matter.

Thus, by applying pressure and cooling , gases can be converted to liquids.

Matter can change state because of Increase or Decrease in Pressure

## Increase in Pressure

When pressure is applied on gas , it converts into liquid

Example

• If we put some gas in a test tube and compress it with help of test tube it compresses (converts into liquid)

## Decrease in Pressure

Due to decrease in pressure, solid can turn into gas

Example

• Solid Carbon dioxide (also called dry ice) gets converted into gas at room temperature,
• This is due to the decrease of pressure to 1 atm (atmosphere)

## What is 1 atmosphere?

The pressure of air in the atmosphere is called atmospheric pressure

The atmospheric pressure of air at sea level is taken to be 1 atmosphere

1 atmosphere = 1.01 × 10 5 pascal

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