1. Air

Air is required for all the living things in the world. We can indeed feel the presence of air even though we cannot see it. We can notice its presence in our day-to-day life while flying a kite, swaying clothes, fluttering pages of a book, and winnowing.

 

Air pressure create winds and also helps in weather forecasting.

The wind is helpful when it is blowing at the back of the person who is flying a kite or rowing a boat.

 

 

While riding a bicycle, it is harder to ride against the direction of the wind. This is due to the air pressure. Even the fluttering leaves, banners, or flags is due to the air pressure when the wind is blowing.

 

To prove that the air exerts pressure, let us take a look at the following.

 

The bicycle runs with the help of the air. The tube of the bicycle is filled with air to keep it tight. When air is pumped inside the tube, the air molecules hit the wall of the tube and exerts pressure. This air pressure inflates the tube from inside and keeps it harder. At the same time, if the tube is overfilled with the air, it may burst.

 

Pumping air into a cycle tyre
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A tin can with a lid is taken, and half of the can is filled with water. The water is heated using a candle flame. After boiling for a few minutes, the candle is blown out, and the can is tightly covered with the lid. One should be very careful while handling the hot can. Then the can is placed in a metallic vessel or a washbasin, and freshwater is poured over it. The shape of the can gets distorted when water is poured on it.

The same experiment can be conducted with a soft plastic bottle. The plastic bottle is filled with hot water. After some time, the bottle is emptied, closed tightly with a cap and shown under the running water. It is observed that the shape of the plastic bottle is distorted on pouring the water.

Cause for distortion:
When water is poured over the hot can or bottle, the steam which is present inside the can or bottle condenses into water. This condensation eventually reduces the amount of air present inside the can or bottle and thus, decreasing the pressure inside. This inside pressure is greater than the air pressure exerted from outside the can. Thus, the can gets compressed, proving that the air exerts pressure.