The Earth we live on is enveloped on all sides by air. Air is a gaseous state of matter. It is a mixture of nitrogen, oxygen, carbon dioxide, dust particles, water vapours, etc. which are all made up of molecules. That means air is a mixture of molecules of many kinds. We know that molecules have their own weight and therefore air which is composed of all these molecules, also has weight.
This fact can be proved by a simple experiment. Take an empty football bladder and a small cord to tie around its neck. Weigh the bladder and the cord in a balance. Now fill the bladder with air and tie its neck with the cord and weigh it again, it weighs more than it weighed when it was empty. Thus, increase in the weight of the bladder is due to the air filled in it. This proves that air has weight. At sea level 0.03 cu m (1 cu ft) of air weighs 0.037 kg.
Because of the weight of air, the atmosphere exerts pressure on every object. This pressure is about 1 kg per sq. cm. Our palm measuring nearly 80 sq. cm experiences a force of 82 kg. If we calculate the total force exerted by it on our body, we find that it is more than the weight of three elephants. We do not feel it because our bodies are supported by equal pressure on the inside of our bodies.
On mountain tops, this pressure is very low. This is because air pressure decreases with the increase in height. But the pressure (inside the body) remains the same at those heights. If the atmospheric pressure is very low as compared to the blood pressure, blood can burst out of nose or ears.
