Why air exerts pressure

You know that we have to fill air into the bicycle tube to keep it tight. Also, you know that a bicycle tube overfilled with air may burst. What is the air doing inside the tube? Discuss with your friends how the air in the bicycle tube keeps it in shape. All these experiences show that the air exerts pressure.

It is due to t his pressure that the leaves of trees, banners, or flags flutter when the wind is blowing. You can list some more experiences which show that the air has pressure. Let us now try to explain why the can or the bottle gets distorted.

As water is poured over the can, some steam in the can condenses into water, reducing the amount of air inside. The pressure of air inside the can decreases than the pressure exerted by the air from outside the can. As a result the can gets compressed. This activity again confirms that air exerts pressure. Winds are caused by variations in air pressure. A wind blows from a region of high pressure to a region of low pressure.

The speed of the wind mainly depends on the difference between the pressures of the air in the two regions. High speed winds are known to blow away thatched and tiled roofs in rural and semi-urban areas. Strong winds can uproot trees and electric poles, and even snap cables. Crumple a small piece of paper into a ball of size smaller than the mouth of an empty bottle.

Hold the empty bottle on its side and place the paper ball just inside its mouth. Now try to blow on the ball to force it into the bottle.

Try the activity with bottles of different sizes. Challenge your friends if they can force the paper ball in by blowing into the bottle. Paheli and Boojho are thinking about the following question: Why is it difficult to force the paper ball into the bottle? Blow the balloons: Take two balloons of approximately equal size.

Put a little water into the balloons. Blow up both the balloons and tie each one to a string. Hang the balloons 8—10 cm apart on a cycle spoke or a stick. Blow in the space between the balloons. Try different ways of blowing on the balloons to see what happens. Can you blow and lift? Hold a strip of paper, 20 cm long and 3 cm wide, between your thumb and forefinger, now blow over the paper. Paheli thinks that the strip will be lifted up.

Boojho thinks that the strip will bend down. What do you think will happen to the paper? Were the observations along the lines you thought? Do you get the feeling that the increased wind speed is accompanied by a reduced air pressure? Why is air pressure greatest at the Earth's surface? What causes hydrostatic pressure in blood vessels? How is hydrostatic pressure created? How does atmospheric pressure change in the troposphere? Does air pressure change with humidity?

How does atmospheric pressure affect boiling points? How is air pressure measured for weather information? How do air pressure regulators work? See all questions in Atmospheric Pressure. 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. 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.