As air is all around us, therefore all things experience air pressure. You would have experienced that cycling against the wind is really difficult. This is because of air pressure. You have learned that winds are actually caused by variations in air pressure. Let us learn how air exerts pressure?

Changes in air pressure bring changes in the weather and also result in the blowing of winds. Air usually moves from an area of high pressure to an area of low pressure and this produces winds. Very few of us realize how strong the air pressure can be. It can be really strong.

Air exerts pressure

Have you ever thought about why it is difficult to ride a bicycle against the direction of the wind? It happens because of air pressure. Let us do an activity to understand what is air pressure? Take a balloon and blow the air from your mouth into it. What made the balloon expand? Yes, this is because of the air you blow into it.

Air pressure inside the balloon is more than the pressure exerted by the air from outside. As a result, the balloon gets inflated. Air pressure is the pressure exerted by the air on different bodies. Actually, air exerts pressure on all bodies at all times in all directions.

Let us now recall some of the experiments.

When you fly a kite, does the wind coming from behind help?

Why is it easier to sail a boat if the wind is coming from behind it? You have to paddle so hard in the strong wind moving at high speed in the opposite direction because it creates air resistance.
Due to air pressure only, leaves of trees, banners, and flags flatten when the wind blows across them.

Air pressure can even distort the shape of a bottle. Take a soft plastic bottle, fill it with hot water. Empty the bottle and immediately cap it tightly. Place the bottle under running water. Why does the bottle gets distorted?

As water is poured over the bottle some steam inside it condenses to form water. The air pressure inside the bottle is less than the pressure exerted by the air from outside. As a result, the bottle is crushed.

Now, let�s see an example.

Take a glass and fill it 1/3rd with water. Cover its mouth with an index card. Now, holding the glass carefully, invert the glass. Now, remove your hand from the card. You see that the card is stuck to the glass amazingly.

Do you know why it is the air pressure that is holding it up? The air outside the glass exerts upward pressure on the card.

As the pressure exerted by air outside is larger than the pressure exerted by the water and the air inside the glass. Consequently, the index card holds and water does not fall out.

Read More- Air Expands on Heating: Explanation with Examples - Science Class 7