### Atmospheric air pressure & Making a barometer

1. Atmospheric air pressure
2. Making a barometer

Importance of atmospheric air pressure
The atmospheric air pressure is extremely beneficial for us, for its absence would have made it impossible for us to drink anything through the straw. Take some water or any other drink of your choice in a glass tumbler. Put two straws into it. Now hold one of the free upper ends of the straw by your mouth and suck in air from it.

This suction will mean that you are drawing out part of the air held inside the straw. The air outside the straw starts asserting the moment part of the air from inside the straw reaches your mouth. It starts putting pressure on the drink to fill in the vacuum created by the air sucked in by you from inside the straw pipe. This process of sucking in the air and filling in the vacuum thus created by the drink continues till the drink remains in the tumbler. The second straw lying in the tumbler remains unfilled by the drink as the conditions of varying air pressure do not apply on it.

Making a barometer
The device used for measuring the atmospheric pressure is called a barometer. Why don't you make one yourself and see how it works and measures the atmospheric pressure?

Take a wide-mouthed bottle and stretch the neck of a balloon clamping it on its mouth. Bind it also with the help of a rubber band in such a way that the balloon is fully stretched on the mouth of the bottle. Now, take a drinking straw and attach one end of it on the center of the stretched balloon with 'Quick-fix' (an adhesive agent). Then, continue to hold the straw in the same position till the 'Quick-fix' gets dry. After accomplishing this, you have to do only one more job  to set a white strip of cardboard by the side of the bottle in such a way that it remains standing upright, just behind the free end of the straw. With the marks indicating 'high and low' degree signs. Now, your barometer is ready.

As you know, when the atmospheric pressure is high, it will exert a similar pressure in all the directions. So much so, that the pressure on all the sides of the bottle will be equal, causing slight deflation in the balloon towards the inside of the bottle. This is turn will put pressure on the attached end of the straw and its other end will rise higher to indicate the increase in the pressure.

On the contrary, if the atmospheric pressure decreases, the balloon will not be deflated. But if the pressure becomes so low as to be even less than the air pressure inside the bottle, it will inflate the balloon and the free end of the straw, quite obviously, will indicate the decrease in the atmospheric pressure.