Does the air weigh anything?
The air seems to be a filmy nothing and most of the time we forget it exists. You might never guess that the air in an empty shoe box can be weighed or that the air in your classroom weighs several hundred pounds The air, of course, is a blanket of gases enfolding the earth and it reaches to perhaps a thousand miles above our heads. Its total weight is many billions of tons.
Imagine an empty square box, one foot in height and width and length. The cubic foot of air inside this otherwise empty box weighs a little more than an ounce, This is not surprising when you remember that air is made of gases and gases are made of atoms and molecules. The solid earth, the seas and all objects in the whole universe also are made from atoms and molecules and it is these small particles of matter which give weight to a substance.
In a cubic inch of ordinary air there are about 300 billion, billion molecules of gas rushing helter skelter at speeds of 1,000 miles an hour. These busy particles of matter give weight to even the smallest quantity of air. And the earthts huge blanket of atmosphere weighs roughly five quadrillion tons which is five followed by 15 zeros.
The weight of the air depends upon its density. When there are more gas molecules crowded into a certain space, the air is denser and heavier, The densest layer of the atmosphere is nearest the surface and the entire blanket becomes thinner and thinner until, far above the earth, it merges with space.
Imagine a square inch column of air reaching from the ground to the top of the atmosphere. We can weigh this filmy column with a barometer and at sea level its weight will be about 14 1/2 pounds.
Three and a half miles above sea level, our column of air will weigh about half this much which means that half the bulk of the atmosphere is packed into a dense layer three and a half miles deep at the surface of the globe. If we weigh our column of air seven miles above the ground, its weight is cut in half again. This air weight is called atmospheric pressure and it varies not only with height but also to some extent with weather conditions. Allowing for slight variations, the atmospheric pressure on the body of a man at sea level is just about 14 tons.
We live our daily lives under this terrific weight of the atmosphere and never notice it. We move this way and that through our ocean of air without effort. But the air only seems to be such a filmy nothing because we have never known life without it. Our bodies are used to it, the muscles are strong enough to cope with it and the body fluids are strong enough to prevent the pressure of air from crushing in upon us.