Peaceful dying out

Hi,
today I will write about the difficulties of calculating the amount of people on Earth and demographic revolution.


For this month’s physics problems that I want to solve, I need to know how much is the number of people in the world increasing. It is just a part of the problem but necessary for the solution. One can quite easily make some simple assumptions and derive an exponential formula that is for any type of reproducing species but does not account in “human” factors. Some of those would take an effect for a population of animals or plants too of course, simply because you do not have an infinite space and other resources. Just an exponential growth would work (I think) for bacteria for example because it is simple to have enough food for LOT of them and they won’t care when they are close to each other[1].

Humanity could be assumed to increase in size in similar fashion during sometimes of its history, for example around the Industrial Revolution when mortality rapidly decreased while natality stayed the same. This did not happen across the whole globe though meaning that in most of the world we were still stagnating. In 21st century the predictions are even worse, the reason is that people in Western world are dying out, meaning we do not have enough babies. The population still increases overall but its thanks to India, Niger or other countries still in the first parts of demographical revolution, that is a part human “evolution” following the decrease and final levelling of natality and mortality. You can read more about that on Wikipedia.

Northern-Western part of the world is dying out. It is probably because people have higher education, which takes longer time and during their career they have less and less time to have and up bring babies. It is fascinating that this effect takes place even in countries with strong religion background, like Poland. I do not find it very sad though, who would think that there could be peaceful dying out?

Dragallur

Disclaimer: I am not a sociologist.

[1] This is actually more complicated and in a sense factually false. There are four phases to the life of bacteria colony and only the second follows what I wrote originally. In the beginning when you put bacteria into some medium, meaning place with “food”, they will start to grow individually in size. This is called the lag phase and after that follows the log phase which is an actuall explosion in the number of bacteria. Here the numbers do grow exponentionally but after they do not have anymore nutrients or there is just too much waste around they will come into a stationary phase where the population is in balance. In the end you might have the death phase but when the onset starts depends on the medium, bacteria etc. The bacteria can reach the density of several billions of cells per millilitre. That is a lot and does take some time if you start with smaller numbers but this proces CAN NOT go on forever.

Generalized bacterial growth curve showing the phases in the growth of bacterial colonies.

Generalized curve for bacteria, note that y-axis is logarithmic

Source: https://www.britannica.com/science/bacteria/Growth-of-bacterial-populations
Picture: “bacteria: bacterial growth curve”. Illustration. Encyclopædia Britannica Online. Web. 31 Oct. 2017. <https://www.britannica.com/science/bacteria?oasmId=127577>

 

 

How it blows

Hi,
tommorow I am writing test on geography, it will be on pedosphere, hydrosphere and atmosphere and since I forgot to learn atmosphere I decided that I will make post about winds and how air circulates on Earth so I can remember it.


The most important thing is that air wants to go from area of high pressure to area with low pressure, this is practicly the key thing in weather forecast because wind also takes rainfall with it and it is key when forming storms.

So it is important to know where are those areas of high and low pressure.

Low pressure areas create when there is warm air which expands thus lowering the pressure and then it rises. This of course happens on equator so there is low pressure always moving just a little bit north and south during year as the angle towards Sun changes.

On poles on the other side is high pressure because cold air falls down and its density increases because it is heavy.

Whole process is not so simple there is no gradient between equator and poles because there are lot other things that change this.

Key picture of winds on Earth

The picture above shows how air travels on Earth, I will start with the area of equator. So there is low pressure because of hot air. It raises and as anti trade wind (in Czech we call it anti-pasát) it goes north or south because the air is pushed by the new air coming. At about 40° the air loses all its humidity and temperature so it goes down. Because it is so dry at those areas deserts tend to create. This is area of high pressure compared to equator so the air goes south as trade wind. It is called like this because it helped sailors when they wanted to trade something. Around equator those winds are weaker and weaker and the air goes up because it is warmer. This area is called doldrums. It is famous for leaving boats powered by wind for weeks on same place, sometimes even killing whole crews since they can not move without wind.

This process described above is called Hadley cell.

Same thing happens around poles except the high pressure area is around poles so winds blow from there. This for example creates what is called tornado valley which is area in USA where hot air from south and cold air from Canada meet to create winds moving spiraly on small area: tornadoes.

It gets much more complicated on what is called Ferrel’s cell which is area between Hadley and Polar cell. Here lot of difference is also made by area above oceans and above land.

Because of Coriolis effect (Earth rotating), trade winds are turned towards west because of their inertia, Earth rotates from west to east.

Dragallur

Check out those two video for coriolis effect and how water turns in toilet: