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Pressure of Air-flow

posted Feb 2, 2015, 2:55 AM by Ranmini Perera   [ updated Sep 23, 2015, 2:29 AM by Upali Salpadoru ]
Ali and Nellie both agreed when air flows, the pressure has to increase. What do you think will happen? If you ask this question from 100 people 98 will say the pressure will increase. How can we test this? Ali scratched his head and thought of an experiment. He kept a  piece of paper on a  table and blew over it, His argument was if the pressure of the air current is low, the paper should go up. If the pressure is high it should get pressed to the table.Try this out.

Fig.1  Blow air between two strips of paper.

The above experiment may not give you a convincing  result. A very easy way to do this is demonstrated here. Take two strips of paper and let them hang down from your hands. Keep the two strips about 5cm apart and blow air in between. If the pressure of the air current is high the strips will move apart. Do the experiment and see what  happens.

 It is unbelievable. It has to be seen to be believed. Another way to study this would be as follows.
Keep a  thin  plastic tube such as a drinking straw dipped in a cup of water. The water may be coloured so that you could see the level clearly.  Take a barrel from a ball point pen and cut it into two. Fix the part with the pointed end to a balloon. Tie it up with a string so that air may not leak. Keep the other part verticlly with one end dipped in water. Now blow the balloon through the jet tube .. Place the jet in line with the opening of the tube and release the air  . Water will get drawn up. Do you know why?


Fig. 2.  Air from a balloon can draw  water .
This is the method used in most of the sprayers. This phenomenon was first discovered by Daniel Bernouli. Read about him in our Biographies.


 Fig.3  Daniel Bernouli  1700 to 1782


•    Build a sprayer (Atomizer)  using this principle.