We don't realize that we are at the bottom of a large volume of air. Just like sea creatures at the bottom of the ocean have the entire ocean's weight on top of them, we do too. Earth's atmosphere is more than hundreds of miles think and we are at the bottom of it and all its weight is pushing on us from the top. This is what is called the Atmospheric Pressure.
Let us know actually see the evidence of this through a simple experiment.
What you will need :
A glass or a cup
Water
A cardboard
Steps to follow :
Pour water up-to the brim and fill the glass / cup
Put the cardboard on top of the cup and hold it it with your palm.
Turn it upside down
Gradually leave your hand / palm supporting the cup.
You will be amazed to see that the water does not gush out. It is held magically against gravity!
The weight of the water pushes the cardboard and tries to gush out, but the pressure of the atmosphere is more than the weight of the cup of water and pushes against it and is more than enough to hold it in place.
This is also what is happening with our bodies. Our internal body pressure is pushing against the atmospheric pressure and the two are in equilibrium. If our body had no internal pressure pressing outwards, then we would all be crushed by the atmospheric pressure.
You can see the evidence of this too.
What you will need :
An empty soda can or a metal container with a lid
Something to seal the opening
Ice
Steps to follow :
Heat the soda can over a burner/kitchen stove for a minute or so,
Let the air inside heat up and partially escape
Now close the opening of the soda can or close the lid of the metal container tightly.
Place the can or the container over a bucket of ice.
You will be amazed to see the can implode as it gets deformed and is crushed by the force of the atmospheric pressure.
As the container cools, pressure inside it drops and becomes less that atmospheric pressure.
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