When you are all thumbs and do something wrong, you will inevitably say, "I don't know anything about common sense." However, we will really be impressed by the "wisdom of parents" because they are really right. However, when we go to the root of the matter and want to ask what the so-called "common sense" is, we can only get a "where there are so many why" with great probability.
Today, let's discuss the ultimate principle of these "common sense".
0 1
When we were young, when we were faced with a bowl of hot porridge for the first time and our mouths were warm, my mother often told us a kind of "common sense of life": drinking while drinking is not hot.
This cognition of "hot in the middle, not hot at the edge" is deeply imprinted in our minds, and even becomes a "muscle memory" when drinking porridge.
This actually involves the knowledge of "heat transfer", which includes convection, contact and heat radiation. The porridge in our bowl is generally viscous and has poor fluidity, so convection heat transfer can be ignored. The delicious "skin" on the surface of porridge makes us slightly eliminate the influence of evaporation. As for thermal radiation, it is a skill that porridge has not yet possessed. Therefore, contact heat transfer can only be used to explain this puzzle.
No matter which grain of rice it is, it will eventually transfer heat to the air, and the porridge on the edge is fortunate to be in direct contact with the bowl wall. The bowl is cooler, the temperature difference is bigger, and the efficiency of porridge "heat dissipation" is higher.
The porridge in the middle will only transfer heat to other rice grains in the bowl that are also "in hot water". The temperature difference between porridge and porridge is small and the efficiency is obviously lower.
Next time you have the opportunity to teach your child to drink porridge from the side, you can expect him to ask "why".
02
Besides eating, dressing and even playing, parents often teach us some "common sense" and "tricks", such as flying kites.
When we were children, when we were flying kites, whenever the kites faltered and fell, experienced adults would tell us, "Take up the line and let it fly higher."
This trick will basically make us cast a "star eye" for our parents (? )。
However, as long as you dare to ask why, you can only get a cold retort: "Ask less why". In fact, the skill of flying kites can be solved by "mechanical knowledge".
Our ideal of flying a kite is that the thread in our hand is put quickly and will not exert force on the kite. If gravity is not considered, the kite will move relatively still with the wind.
However, the fact is cruel, because of the influence of surrounding buildings and topography, the airflow is unstable, the wind speed and direction are capricious, and the kite can't overcome gravity and will naturally fall.
When a kite flies in the sky, it has an angle with the horizontal. When the airflow brings upward lift, the kite will fly higher. When the line is closed, the line becomes shorter and the angle between the line and the ground increases; Putting a string again can make the kite reach a balance point again at a higher and farther place, and it will naturally save the trouble of "crash" after repeating the action.