An uncle is walking leisurely in front of you, and suddenly, you catch a glimpse from the corner of the screen of your phone, the uncle's right hand, which was originally behind the back, is gone - not good! It's too late, you want to dodge, but it's too late, a fierce white smoke hits your face, and a silent slap hits your face the three flavors that spew out of the uncle's chest True qi are being inhaled by you without any prejudice.
Countless times, this kind of unpredictable attack on the road almost never misses. What's unpleasant is that the person in front of him, who didn't know anything about it, still took a sip from time to time and continued to enjoy his happiness. Now every time you walk outside, you'll keep an eye out for someone who's smoking ahead. If there is, the best solution is to rush ahead of him and leave him as far behind as possible.
Life experience is always summed up through countless experiments. Since it is always so consistent, there must be physical laws that describe and predict it. As someone who likes to think, there are obviously physical problems behind this that you need to clarify.
Why can't the smoke stay in place, or gather further, but always separate?
We usually observe the movement of a particle, it can move back and forth, such as a simple pendulum. But we've never seen anything like this happen with a system of many particles. Any system involving a large number of particles is a thermal system. The evolution of a thermal system always proceeds in a spontaneous direction, and the process in the opposite direction cannot occur automatically, which is the irreversibility of the thermodynamic process.
For example, a hot object will automatically transfer heat to a cold object, not the other way around; the work of friction will cause mechanical energy to be converted into thermal energy, but the thermal energy cannot be fully converted back into mechanical energy; the gas in the container will gradually diffuse into the entire container space, It will not automatically shrink to one part; after mixing solutions of different concentrations, the concentrations in various places will reach the same level, and will not automatically return to unevenness. 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, and it always spreads out automatically instead of gathering.
In the container shown above, without any external factors, the gas molecules will disperse each other until they are nearly uniformly distributed in the container. We call this process diffusion, which refers to a phenomenon in which particles migrate from places with high density to places with low density when the particle density distribution is not uniform.
Gases diffuse without agglomeration, which is determined by the second law of thermodynamics. According to this law, the automatic process of all thermodynamic systems is to make the structure and state of their internal components tend to be 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 increasing entropy. As the gas diffuses, the molecular positions become more diverse and more chaotic, in line with the requirement for an increase in entropy.
How fast is the diffusion? Can it really be so fast that the people next to it can't be avoided in an instant?
Diffusion is caused by the density difference inside the system and is also affected by factors such as the internal pressure difference, temperature difference, and the type of particles, so diffusion is a very complex problem. If we simply consider 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 nanometers, the viscosity is 300K, and the diffusion coefficient is approximately visible if only simple diffusion is considered, the particles move a distance of 10 microns per second.
This shows that just relying on simple diffusion, it is impossible for the smoke to hit the face in an instant! Therefore, the fact that the smoke can spread so fast is caused by more factors and mechanisms. When considering various factors such as pressure difference, temperature difference, and airflow in the open space, the actual diffusion rate will be very fast.
At the same time, it should also be taken into account that the human nose is highly sensitive, and even a small amount of smoke drifting over is enough to cause discomfort. Therefore, although the lingering smoke seemed to be unhurried, it suddenly rushed into the nostrils, and the internal organs were completely smoked, even if it was several meters away.
Why does it feel like the smoke is always floating backward?
Looking around, the weather is fine, there is no wind at all. It is said that the zero-level smoke column is going straight to the sky, but why does the smoke from the mouth always go backward? Very simple, the reason lies in you, because you are moving forward. Behind this involves a simple physical knowledge - relative motion.
For the ground, the smoke is originally stationary in the horizontal direction, but relative to you or the smoker, the smoke has a backward speed, so you will see the smoke coming straight at you, the faster you go, the smoke is attacked at an even sharper speed.
Why do we always feel the breeze blowing when we walk? Yes, the faster you go, the stronger the wind will get.
Why smoke should be heavier than air, but it rises?
The smoke consists of partially burnt hydrocarbons. These are solid particles that are supposed to fall to the ground due to gravity. So why do they rise? Because usually, combustion produces smoke, which must be accompanied by heat release, raising the temperature of the surrounding air. The hot air is now lighter than the cold air and begins to rise, and the rising air pushes the solid particles upward against gravity.
Some people say that smoking while walking blows away toxins and also helps with exercise, is that true? 100% rumor! When walking and smoking, the total amount of cholesterol and free fatty acids in the blood increase, which can lead to the production of atherosclerosis. In addition, walking and smoking can cause glandular hyperplasia in the trachea and bronchi and aggravate the inflammatory reaction of respiratory ulcers.
If you smoke while walking, with the increase in smoking time, the long-term exposure of organ mucocilia to cigarette smoke will hinder the ability of human respiratory mucosal fibers to eliminate dust, and the probability of acute bronchitis will increase. When a person is in a state of exercise, the breathing rate is faster than that in a quiet state, the ventilation function of the alveoli is accelerated, and the blood circulation and metabolism of the human body are also accelerated. Harmful substances inhaled are more likely to enter the alveoli and circulate more easily into the bloodstream.
Carbon monoxide will be produced after the cigarette is burned. In addition to the acceleration and deep enhancement of the respiratory rate during human exercise, the concentration of carbon monoxide inhaled by the human body in the blood exceeds 40/10,000, which will affect the oxygen transport function of the blood.
Some people may say: Now it's only indoor smoking, right? There are no restrictions outside. is that so? of course not! The following is the content of the scope and measures for the prohibition of smoking in Chapter II of the Regulations on the Control of Smoking in Public Places:
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:
Outdoor areas of public places where minors are the main activity crowd, such as kindergarten institutions, child welfare institutions, schools, activity centers, and education and training institutions;
Outdoor teaching areas of colleges and universities
Outdoor areas of maternal and child health care institutions, children's hospitals, and maternity hospitals
Outdoor spectator seats and arena areas of sports and fitness venues;
Outdoor waiting areas of public transport
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 have no restrictions, so accusing a passerby of smoking has no legal basis. However, some countries and regions, such as Japan and Hong Kong, are advising people not to smoke while walking. The chimney of a steel mill affects a city, a cigarette favors a bus car, and smoking on foot is like a moving chimney, with a tail dragged dozens of meters away. Of course, we should also be considerate of smokers, after all, they are victims too! But hopefully, there will be fewer and fewer such moving chimneys.
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