Air is one of the most mundane substances around us. It is colorless, odorless and amorphous, yet everywhere – we cannot escape from it. On the small scale, air consists of multiple types of molecules, some of which are crucial for the organisms on earth; while on the large scale, air forms the atmosphere of earth, which essentially is the reason why lives can exist on earth. Today, let’s look at air from different prospective and on the way unfold some secrets of air that you may not know.
1. 21, 78, 3, 3, 94
If you have taken some high school chemistry, this array of numbers may look familiar to you – at least for me, I used this recipe to cram for my chemistry exams. This array stands for the proportions of each kind of gases that consists air. A common mistake that the general public may make is that, air is made of “air molecules”. In fact, the commonly used term, air, refers to a collection of gases including oxygen (denoted by O2), nitrogen (N2), carbon dioxide (CO2), argon (Ar), and some other kind of gases. By volume, air contains approximately 21% oxygen, 78% nitrogen, 0.03% carbon dioxide, 0.03% other gases, and 0.94% noble gases, of which primarily is argon.
2. The weight you cannot bear
Air seems to be weightless. The situation does not usually happen where you have to make tremendous efforts to just stand up because the air on your shoulders is too heavy. However, air does have weight, and it IS heavy. Let’s verify this argument through some simple math. The air pressure, defined by the force exerted on a unit area, is about 105 Newton per square meter. The area of your shoulders is about 15 cm * 40 cm = 6 *10-3 m2. This gives the force on your shoulder by air, F = 6 *10-3 * 105 = 600 Newton = 135 pounds! Well, apparently you do not feel this weight every time you stand up (in addition to your own weight, of course), so how come? The magic spell is that, air is everywhere! This is saying that, while there is 135 pounds of force on your shoulder, there is also the same amount of force from below that “lifts” you, as long as there is air that you “stand on”. Therefore, you should now understand why the suction cup can “stick” your GPS receiver on your wind shield – there is practically no air in the suction cup, so the atmospheric air pressure keeps it there.
3. Refund!!! There is “water” in my bottle of compressed air!
Some of you may have used compressed air to blow off the dust on your laptop. When you shake the bottle, you will typically hear the sound of “water” pounding on the interior of the bottle. Why there is “water” in the bottle? In fact, the “water” is actually air! Air does not necessarily have to be in the gaseous state, and it can change from a gas to a liquid or even to a solid when you, for example, compress it to a very high pressure. In this case, the pressure forces the molecules to stay closer to each other, and air appears to be a liquid. (Actually, this is the ultimate difference between a liquid and a gas – the molecule spacing.) In practice, this is how people usually store gases – in a steel, high-pressure bearing tank – so that it would be volume efficient.
4. Wind – a troublemaker but also a blessing
When there is a pressure difference of air between two regions, maybe caused by the different temperatures, air will flow from the high pressure region to the low pressure region. This process creates one of the most common natural phenomena – wind. In a hot summer day, a breeze is almost bliss. However, you do not want the wind to blow too hard; too fast the wind might be detrimental. Tornado is a wind of this kind. Wind is also one of the reasons that accounts for a phenomenon called ocean current. Ocean current is a continuous, directed movement of seawater. The constant winds in the high seas (far away from shore) direct the surface sea water to move along with the winds due to friction, so ocean current forms. Ocean current is a very important phenomenon – it is a dominant factor in determining the climate of many regions! The most striking example is the Gulf Stream, an ocean current originates at the tip of Florida and extends towards Europe. The consequence is that, due to the Gulf Stream, northwest Europe is actually much more temperate than any other region at the same latitude. The famous Peruvian anchoveta fishery is also a result of ocean current, where ocean current brings abundant nutrition to the area.
Although air is so unnoticeable, it affects our lives in nearly every aspect, either directly or indirectly, just as its universal presence. It protects all the organisms on earth surface from serious cosmic radiation, and retains heat on earth so that the temperature on earth surface would not vary dramatically. I would like to end our investigation of air with a question: air is an important industrial raw material. What is air making?