What is Air Pressure
The pressure exerted by air is called air pressure. The air in the atmosphere exerts pressure on every object and in all directions (up, down, left, right, etc.). The pressure exerted by the atmosphere depends on many factors. For example, it depends on the height of a place and also on the temperature. Generally, places at a lower temperature are at a higher pressure than places at a higher temperature. Air moves from an area of higher pressure to an area of lower pressure. This causes wind. The converse is also true. Moving air causes a variation in pressure.
Activity
Aim: To show that air exerts pressure (adult supervision required)
Materials needed: A tin/thin metal can with an air tight cap, a stove/Bunsen burner, kitchen sink/wash basin, tongs to hold the hot can, and a small thick towel.
Method:
- Fill the can up to about one-third with water.
- Heat the can without the cap and let the water boil for some time. Make sure a lot of steam escapes.
- Take the help of an adult to remove the can from the stove using tongs, and quickly cover the opening and close the cap tightly using the thick towel.
- Take the can to the kitchen sink/wash basin and hold it under the tap water and see what happens.
Observation: The can slowly crumples up.
Conclusion: This happens because when the can is heated, the steam produced pushes out most of the air in the can. When it cools down, the steam in the can condenses and leaves a near vacuum in the can (except for the remaining water), and the pressure of the air outside the can is large enough to compress and crush it. This shows that air exerts pressure.