Air Exerts Pressure (With activities)

Air Exerts Pressure

The envelope of air surrounding the earth is called atmosphere. Air has weight. The weight of air presses our bodies all the time. This weight of air acting on a surface causes air pressure. 

Some daily life experiences that show that air exerts pressure

  • You find it easier to row the boat when the wind is blowing behind you.
  • The wind coming from the back help in flying kite.
  • When we suck from the straw, the liquid rises in it.
  • The medicine enters the syringe when a piston is pushed out.

Activity I

  • Materials Required: tumbler, water, square cardboard piece
  • Method: Fill up the tumbler with water up to the brim. Cover it with cardboard piece and turn the glass upside down. Slowly remove your hand.
  • Observation: Cardboard does not fall and water stays in the glass.
  • Inference: air pushes the cardboard up and prevents it from falling.

Activity II

  • Materials Required: plastic bottle with cap, hot water, cold water
  • Method: Pour hot water into the plastic bottle. Empty the bottle and put the cap tightly. Pour some ice-cold water on it.
  • Observation: The bottle will get de-shaped.
  • Inference: The air from the bottle expands as it becomes hot. When it is cooled, air contracts. The outside air has more pressure and it crushes the bottle.

High-speed winds are accompanied by reduced air pressure. Let us now perform certain experiments that will show that high-speed winds reduce the air pressure.

Activity III

  • Materials Required: Two balloons
  • Method: Blow the balloons and tie string to it. Hang them 10 – 12 cm apart on a rim. Blow air in between the balloons.
  • Observation: The balloons will move closer.
  • Inference: The air pressure between the balloons is reduced due to more speed. Air moves from higher pressure to lower pressure bringing the balloons closer.

Activity IV

  • Materials Required: Bottle, crumpled piece of paper
  • Method: Crumple a small piece of paper into a ball of a 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.
  • Observation: The paper does not move inside.
  • Inference: The air pressure at the mouth of the bottle is reduced due to more speed. This forces the air out from the bottle. This prevents the crumpled paper ball to move inside.

Question For You

Q1. Give Reason – Why is the roof of houses blown off when a strong wind is blowing?

Ans: The strong wind above the roof lowers down the air pressure just above the roof. This forces the air from the air to move outward blowing off the roof of the house.

Q2. A child blows air with a straw near the opening of another straw which has its other end in a soft drink bottle. What do you think will happen and why?

Ans: The level of soft drink will rise in the bottle. This will happen because the air pressure is reduced above the straw hence the drink will rise in it. 


#rainbowz 

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