Concepts

Class 8
Chapter 11 Class 8 - Force And Pressure

## Pressure Exerted by Liquids

We know that all liquids have weight

Example-Water has weight

When this liquid gets filled inside a container,it exerts pressure because of weight of liquid

### Example 1 Attaching Balloon to Test Tube

Suppose we attach balloon with test tube

We will fill the test tube with some water

It makes the balloon bulge a little

We put some more water in test tube

It makes the balloon bulge even more

This shows that water exerts pressure on balloon(more the water,more pressure is exerted on balloon

### Example 2 Hole in Water Bottle

We know that water flows through water Bottle

if there is hole in water Bottle,water comes out very fast like a fountain

This shows that water exert pressure on bottle.

## Gases Exerting Pressure

We know that there are many gases like Nitrogen, Oxygen, Carbon Dioxide in the atmosphere

When these gases come in contact with a substance, there is collision of molecules of gas with molecules of substance

This causes air pressure

### Example 1 - Inflating a balloon

When we inflate balloon,air comes inside the balloon because of pressure exerted by molecules of air on the balloon Due to this balloon inflates

We have to close its mouth

If we do not close its mouth,air escapes out

This shows air has pressure

### Example 2 - Filling air in bicycle tyre

When air is filled into bicycle tyre by using a pump,the tyre tube gets hard because of pressure exerted by molecules of air on tyre tube of bicycle

If bicycle tyre gets punctured,air escapes very fast

This shows air has pressure