Atmospheric Pressure

Question 1 Define the term atmosphere?

Question 2 What is atmospheric pressure?

Question 3 What is the SI unit of atmospheric pressure?

Question 4 What substance present in our body to balances the atmospheric pressure acting on us?

Question 5 Where will be the atmospheric pressure be greater-at ground level or at the top of high mountain?

Question 6 Name the substance whose weight produces atmospheric pressure?

Question 7 Describe one activity to show the existence of atmospheric pressure?

Question 8 Why do mountaineers suffer from nose bleeding at high altitude?

Question 9 what is the cause of atmospheric pressure?

Question 10 Why are our bodies not crushed by the large pressure exerted by the atmosphere?

Question 11 Why atmospheric pressure decreases as we go higher up above the earth’s surface?

Atmosphere

The layer of air above the earth is called atmosphere.

The air in our atmosphere extends up to 300 kilometres above the surface of Earth.

The atmosphere contains a tremendous amount of air. Air has weight so the atmosphere consisting of tremendous amount of air has enormous weight.

Atmospheric Pressure

Atmospheric pressure is the air pressure which is exerted by the weight of air present in the atmosphere.

Atmospheric pressure is due to the weight of air present in the atmosphere above us. Atmospheric pressure also acts in all directions. On the surface of earth, the atmospheric pressure is maximum at the sea level. This is because the column of air above us is tallest at the sea level .The atmospheric pressure on the surface of earth is 101.3 kilo Pascal.

As we go up in the atmosphere from the surface of earth, the atmospheric pressure goes on decreasing. This is because as we go up in the atmosphere, the weight air above us goes on decreasing. So  the atmospheric pressure on the top of a hill mountain will be much less than at its base.

The common unit for expressing and measuring atmospheric pressure is millimetres of mercury .The atmospheric pressure on the surface of earth is 760 mm of mercury.

Activity : The existence of atmospheric pressure

A glass tumbler is filled to the brim with water and covered with a piece of thick and smooth card. We press the card hard so that there is no air in the glass tumbler. Keeping the card in position with one hand we invert the glass tumbler full of water. The hand supporting the card is then withdrawn slowly. We will see that the piece of card does not fall through the tumbler is full of water and exerts pressure on the card in the downward direction. The cards does not fall because the atmospheric pressure acts on the card in the upward direction and holds the card in place. The upward atmospheric pressure acting on the card is greater than the downward pressure of water on the card.

Our body has a liquid called blood which flows through the blood vessel into each and every cell of our body. Our blood itself exerts a pressure called blood pressure which is slightly greater than the atmospheric pressure. Since the atmospheric pressure acting on our body is balanced by the blood pressure acting from inside, we do not get crushed.

The atmospheric pressure is maximum on the surface of the earth. When we go to high altitude then the atmospheric pressure decreases. At high altitude the atmospheric pressure becomes much less than our blood pressure. Since our blood is at higher pressure then outside pressure, therefore, some of the blood vessels in our body burst and nose bleeding take place at high altitude .Thus nose bleeding usually occurs in those people who trek to high mountains.