Shulou(Shulou.com)11/24 Report--

An uncle is walking leisurely in front of you. Suddenly, you catch a glimpse of my right hand with the back of your phone screen. It's not good. When it was too late, you were anxious to dodge, but it was too late, a fierce white smoke hit your face, a silent patter hit your face-you inhaled all the three real smells emitted from my chest.

Countless times, such unexpected attacks on the road almost never miss. Unpleasantly, the previous initiator knew nothing about it and still took a bite from time to time to continue to enjoy his happiness.

Now every time you walk outside, you will pay attention to whether there are smokers walking in front. If so, the best solution is to rush in front of him and leave him as far behind as possible.

But sometimes, someone smokes in front of him, but because of the large number of people, or the narrow road, there is no way to overtake him, so he can only punch him in the face. That kind of taste is like being smelled fart by the head, which is very uncomfortable.

The experience of life is always summed up by countless experiments. Since it is always so consistent, there must be physical laws to describe and predict it. As a thinker, there are obviously physical problems that need to be clarified.

The first question: why can't the smoke stay in the same place or gather further, but always separate?

We usually observe the motion of a particle, which can move back and forth, such as a simple pendulum. But we've never seen anything like this happen to a system made up of a lot of particles.

Any system that involves a large number of particles is a thermal system. The evolution of the thermal system is always carried out in a spontaneous direction, while the process in the opposite direction can not occur automatically, which is the irreversibility of the thermodynamic process.

For example, hot objects will automatically transfer heat to low-temperature objects, not vice versa; work done by friction will cause mechanical energy to be converted into heat, but the heat cannot be completely converted back into mechanical energy; the gas in the container will gradually spread into the whole container space, instead of automatically shrinking to a local; after the solution of different concentrations is mixed, the concentration in each place will be consistent and will not automatically return to non-uniformity.

Therefore, the following animation is unreasonable.

For a cloud of smoke, fine particles, because it contains a large number of particles, its evolution process is also directional, it always spreads rather than gathers automatically.

In the container pictured above, without any external factors, the gas molecules will disperse from each other until they are nearly uniformly distributed in the container. We call this process diffusion, which refers to the phenomenon that particles migrate from high density to low density caused by the uneven distribution of particle density.

The gas automatically diffuses without gathering, which is determined by the second law of thermodynamics. According to this law, the automatic process of all thermodynamic systems tends to make the structure and state of its internal components more chaotic.

The physical quantity that describes this degree of confusion is called entropy, so the second law of thermodynamics is essentially the principle of entropy increase. After gas diffusion, the positions of molecules become more diverse-more and more chaotic, in line with the requirements of an increase in entropy.

The second question: how fast is it spreading? Is it really fast enough for the people next to you to avoid it in an instant?

Diffusion is caused by the density difference within the system, and is also affected by the internal pressure difference, temperature difference and the type of particles, so diffusion is a very complex problem.

If we simply look at the diffusion caused by Brownian motion, we use the Einstein diffusion coefficient, which is the particle radius and the fluid viscosity. If the particle radius is 10 nm, the viscosity is 300K, and the temperature is 300K, the diffusion coefficient is about visible. if only considering the simple diffusion, the particle moves only 10 microns per second.

This shows that only by simple diffusion, the smoke can not be fast enough to hit the face in an instant!

Therefore, the smoke can spread so quickly, is caused by more factors and mechanisms. When considering various factors such as pressure difference, temperature difference and airflow of smoke in the open space, the actual diffusion speed will be very fast.

At the same time, it should also be taken into account that the human nose is so sensitive that even a small amount of smoke is enough to cause discomfort. Therefore, although the leisurely smoke looked leisurely, it came to the nostrils in an instant, and the internal organs were so thoroughly smoked that it could not be spared even a few meters away.

The third question: why does it feel like the smoke is always floating backwards?

Look around, it's a nice day, there's not a breath of wind. Generally speaking, the zero column of smoke soars into the sky, but why does the smoke from the population always try to run backwards?

Very simply, the reason is on you, because you are moving forward. This involves a simple knowledge of physics-relative motion.

For the ground, the smoke is originally stationary in the horizontal direction, but for you or the smoker, the smoke has a backward speed, so you will see the smoke coming straight at you, and the faster you go, the faster it will hit you head on.

A similar question is: why do we always feel the breeze on our face when we walk?

Yes, the faster you walk, the stronger the wind will become.

The fourth question: why does smoke rise when it should be heavier than air?

The smoke consists of partially burned hydrocarbons. These are solid particles, which should have fallen to the ground because of gravity. Then why did they rise?

Because usually, combustion produces smoke, which must be accompanied by the release of heat, raising the temperature of the surrounding air. Now the hot air is lighter than the cold air and begins to rise. The rising air pushes the solid particles upward against gravity.

One last question: some people say that when you smoke while walking, the toxins are blown away and it helps to exercise. Is that really the case?

100% rumors!

When walking and smoking, the total amount of cholesterol and free fatty acids in the blood increase, which will lead to atherosclerosis. In addition, walking and smoking can cause glandular hyperplasia of trachea and bronchi and aggravation of inflammatory reaction of respiratory ulcer.

If you smoke on the side of the road, with the increase of smoking time, organ mucosal cilia will be exposed to cigarette smoke for a long time, which will hinder the dust removal ability of human respiratory mucosal fibers, and the probability of acute bronchitis will increase.

When a person is in a state of exercise, the breathing rate is faster than when it is quiet, the ventilation function of the alveoli is accelerated, and the blood circulation and metabolism of the whole body are also accelerated. Inhaled harmful substances are more likely to enter the alveoli and circulate more easily into the bloodstream.

Carbon monoxide will be produced after cigarette burning, coupled with the acceleration and depth of respiration during human exercise, so that the concentration of carbon monoxide inhaled in the blood exceeds 40/10000, which will affect the oxygen delivery function of the blood.

Some people may say: now it's just indoor smoking, right? There are no restrictions outside.

Is that so? Of course not! The following are the contents of Chapter II of the regulations on the Control of smoking in Public places concerning the scope and measures to prohibit smoking:

Article 10 smoking is prohibited in all indoor public places.

Article 11 smoking is completely prohibited in the outdoor areas of the following public places:

(1) Outdoor areas of public places with minors as the main activity groups, such as child care institutions, child welfare institutions, schools, activity centers, education and training institutions

(2) Outdoor teaching areas of institutions of higher learning

(3) Outdoor areas of maternal and child health institutions, children's hospitals and maternity hospitals

(4) Outdoor spectator seating and competition area of sports and fitness venues

(5) Outdoor waiting areas for public transport

(6) other outdoor places where smoking is prohibited as prescribed by laws and regulations.

Therefore, there are many places outside where smoking is not allowed!

Of course, most outdoor spaces are not restricted, so there is no legal basis to blame a passer-by for smoking. However, some countries and regions, such as Japan and Hong Kong, China, advise people not to smoke when walking.

The chimney of a steel factory affects a city, a cigarette favors a bus carriage, while walking smoking is like a moving chimney, with a tail dragging dozens of meters away.

Of course, we should also be considerate of smokers. After all, they are also victims. But it is still hoped that there will be fewer and fewer moving chimneys.

This article is from the official account of Wechat: University Physics (ID:wuliboke), by Xue Debao.

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