Amazing knowledge

Chapter 11 Science Talk Show: The World of Science Students is Different

*How strong is the radiation of the X-ray security inspection machine?
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Interesting: ★★
There are rumors that the radiation inside the security inspection device is very large, almost comparable to the radiation received by an X-ray taken in a hospital!If this is the case, can you still pass the security check happily in the future?
As more and more security inspection machines are settled in railway stations and subways, X-ray security inspection machines have become common instruments in our daily life.

When some people hear that the radiation from X-ray security inspection equipment is very strong, they even become cautious when taking subways and trains, because there will be safety inspections every time, and how can their bodies survive being exposed to such radiation every day?
In fact, X-ray security detectors are not that scary at all. The security detectors do emit radiation, but the radiation intensity is so small that it is almost negligible. After all, our mobile phones still have radiation. We don’t carry our mobile phones with us every day.

Don’t ignore one problem, whether it’s the airport security staff or the subway staff, they stay with the security machine all day long, and they are the first to bear the brunt of radiation, but don’t you see that they still happily stick to the “radiation number one” every day? line".

Luggage security inspection equipment and medical X-ray diagnostic equipment are originally the same family, and they have something to do with X-rays. However, in terms of radiation, luggage security inspection equipment does not even have 1% of X-ray medical diagnostic equipment. X-rays are obviously still Get closer to a medical diagnostic instrument.

Even if you go in and out of the subway every day, the amount of radiation accumulated over a year is not a big deal.The U.S. Centers for Disease Control and Prevention has conducted a radiation dose survey on security personnel at six major airports, and the results show that the radiation dose received by the staff is far below the upper limit of radiation dose that humans can accept.

So the next time you cross the subway, you can go forward boldly, as long as you don't leave anything behind.

The final word: The radiation of the X-ray security inspection machine is very small, completely within the safe range, even if it is in contact with the X-ray security inspection machine every day, it will not have any impact on the body.

*Did Franklin really experiment with kites?

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When I was in elementary school, I read the heroic deeds of the great scientist Franklin from the textbooks. It is said that Franklin used a kite to do experiments and proved that lightning is also electricity.Is this matter true or false?
If "Franklin's kite experiment existed and was successfully carried out" is a true proposition, then "Franklin was still alive and kicking after the experiment was successful" is a [-]% false proposition.Unless you have an indestructible body, after being struck by lightning, all that is left is a charred corpse.

Because lightning has condensed a huge amount of energy before it passes through the clouds and reaches the ground, if the lightning comes into contact with the human body, the current released instantly will reach tens or even hundreds of kiloamperes.And if a fragile human being feels even a few milliamps of current, it will cause the heart to stop and the brain to freeze.

As the story says, "Franklin stretched his finger towards the key and was shocked", which is a "direct shock". It is impossible for Franklin to go back and tell others about his discovery after being shocked. , because even if he didn't go to see God at this time, he only had half his life left.

In short, Franklin may have really experimented with a kite, but he certainly would not be as described in the story, at most he would be hit by the static electricity on the kite. If he really had close contact with the thunder and lightning, this experiment might be Franklin's life. The last experiment in .

The final word: If you feel the lightning through the metal key on the kite, it is equivalent to suffering a direct lightning shock.Lightning shocks can kill people instantly, and it was impossible for Franklin to complete the experiment as described in the story.

* Can the balloon really pull the cabin and fly?
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Friends who have watched "Flying House Adventures" must still remember that the old man in the story tied his house to a bunch of balloons, and the house flew up like this, so a wonderful adventure began.So now the question is, can the balloon really fly with the cabin?
In fact, this is really doable.The National Geographic Channel of the United States has done this experiment specifically.They built a 5-meter-square and more than 5-meter-high wooden house. In order to improve the success rate of the experiment, the researchers specially chose wood with a lighter texture.

In the end, the staff tied 300 high-altitude balloons filled with nitrogen to the cabin, and then it was time to witness the miracle: the cabin really flew into the air waddling.

But it would be too boring for the game to end like this. After all, no one's house is a wooden shell at best, so the people from the National Geographic Channel threw two hot air balloon pilots into the wooden house, but the wooden house is still stable as the local "flying house". "In mid-air.

The balloon took the wooden house to an altitude of 3000 meters and flew back and forth for an hour.

If you are interested, maybe you can also take a flying trip, but before flying, you must think about how to get out of the "flying house" at that time. You can't use a small needle to puncture the balloons one by one, right?
The final word: As long as the house is light and the number of balloons is sufficient, the house can indeed fly.

*Does "invisibility cloak" really exist?

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Knowledge: ★★★★
Interesting: ★★★

Clairvoyance, wind ear, touch stone, invisibility, and wall piercing, these are all magical skills that can only be found in fairy tales.However, with the advent of mobile phones, clairvoyance and wind ears are no longer a problem. From this point of view, it seems that the invisibility cloak is not impossible!Are there any invisibility cloaks in today's society?
In fact, from the perspective of today's scientific and technological development, the invisibility cloak is possible, but it does not have such a powerful function, and it has certain restrictions, such as a specific environment, a specific angle, and so on.

First of all, the reason why people can see things is because the light waves cannot pass through the objects smoothly after they hit the objects. The reflection and shadows produced by the light waves are all ways to help us see objects.In this way, as long as the light wave can go around the object when it sees it and remove all obstacles, then the object will really "disappear" from our sight, and the invisibility cloak will be successful.

But in fact, materials that allow all light waves to go around are even harder to find than UFOs!The best result so far is the invisibility cloak designed by the Royal University of London, which can allow visible light and electromagnetic radiation to go around obediently, but there are other members in the light wave, and these members are not so easy to handle.

Although there is a long way to go, the rudiment of the invisibility cloak already exists. I believe that the "I can see you, you can't see me" that only appeared in movies will be staged in real life in the future.

The final word: the current technology cannot create a real invisibility cloak, and whether the invisibility of an invisibility cloak depends mainly on the material. I believe that in the modern age of rapid technological advancement, it is not impossible to invent an invisibility cloak.

*Why can't a time machine be built?
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As time-travel dramas are rampant on TV, "time-travel" has become a hot word at the moment. If there is a time machine to take us back to ancient times, it will definitely be a different experience.However, so far, no one has successfully built a time machine. Why?

First of all, if the time machine really exists and successfully sends people back to the past, this involves a classic "grandfather paradox".That is, if someone goes back to the past and kills his grandfather, when his grandfather died, someone's father was just a "tadpole" with no destination.

So here comes the question, the grandfather is dead, and the father is not even a shadow, so where does "someone" come from?Does the society he lives in still exist?
Even if we put aside the "grandfather paradox" and assume the existence of parallel time and space, time machines cannot be built, because the properties of time determine its irreversibility.Although there is a theory of relativity that proves that when the speed of an object approaches the speed of light, time will slow down, but this is only a "relative" concept. Time itself does not reverse, it just goes slower than the "time" we are familiar with.

If you want to time travel, forget it, it's better to think about what to have for dinner.Whether it is from the theory of relativity, quantum mechanics or the second law of thermodynamics, it is impossible to create a time machine. If there is such a thing, there should be someone from the future society to "say hello" to us "ah!

The final word: The irreversible nature of time determines that the time machine can only be a beautiful fantasy in everyone's mind. At least the existing theories cannot make "time travel" justified. The future is still unknown, but it is currently impossible to create a time machine.

*Why does hot water freeze faster than cold water?
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Knowledge: ★★
Interesting: ★★★★
According to our usual thinking, if a glass of cold water and a glass of hot water are put into the refrigerator at the same time, no matter how you look at it, the glass of water with a lower temperature will freeze first.But the reality is always so cruel, the cold water lost to the hot water in the matter of freezing!They freeze faster than hot water!why is that?
In fact, this is not the fault of cold water, they are just "slow heat".Although cold water freezes slowly, the ice that freezes in cold water is solid ice. Unlike hot water, it only does superficial work, and the job is done by forming a layer of ice on the surface.

Because the hot water itself has a relatively high temperature, it will evaporate part of the water first. In this way, the starting line between the cold water and the hot water will be separated in an instant.

Furthermore, the temperature of the hot water has forced away a lot of the gas that was originally dissolved in the water. In contrast, the gas dissolved in the cold water is more.

When the temperature changes, the gas will automatically form convection. There are more dissolved gases in the cold water, and the convection in the water is also relatively strong. These convective movements also add a lot of resistance to the freezing of cold water.

In fact, this phenomenon has a tall name called "Mpemba effect". There are many reasons for this effect. The convection and evaporation mentioned above are all tenable explanations, but these explanations are only supported by experiments and have no theoretical data. calculation.

This question has troubled scientists all over the world for a long time, but they have not found an accurate and perfect answer. In order to find an explanation that has both experimental and theoretical support for the fact that cold water freezes slower than hot water, That still depends on the efforts of scientists to explore!

The final word: there is less dissolved gas in hot water, and hot water evaporates more easily. These are the reasons why hot water freezes faster than cold water, but scientists all over the world have not found a convincing explanation for this phenomenon. explanation of.

* Why are diamonds so hard?
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"Diamonds are forever, and one piece lasts forever." Diamonds are the hardest substance in nature. What is it that makes diamonds have such a strong hardness that kills all other substances in seconds?

In fact, there is nothing special inside a diamond, just a bunch of carbon atoms, which are very common atoms in nature.Graphite is also full of carbon atoms like this. From a microscopic point of view, diamonds and graphite are like brothers who can't get closer.

But what is graphite?The pencils we use for writing contain a lot of graphite. Graphite is a very soft substance, softer than our nails. Everyone is made of carbon atoms. Why is there such a difference?

The reason why graphite and diamond are so different is because of the position of the carbon atoms inside.We know that in a planar structure, the most stable shape is a triangle, but in a three-dimensional structure, the most stable structure is the arrangement and distribution of carbon atoms in diamonds.

There are 4 carbon atoms around each carbon atom in the diamond and it is tightly close together hand in hand, such a dense three-dimensional structure is unmatched by any substance in nature.

The density of diamond can reach 3.5 grams per cubic centimeter, which is 1.5 times that of graphite. Compared with graphite, the "average atomic footprint" inside diamond is very tight.

There is not enough space, and the structure is packed together. It is just like this that the carbon atoms that are packed to the brim create the hardest substance in nature.

Only when there is pressure can there be power. The hardness of diamonds can be said to be squeezed out.

But the hardness does not mean that the strength is also great!Diamonds are just not easy to scratch marks, they will shatter when dropped on the ground, and they will also be cut into different shapes.

The final word: The hardness of diamonds is so great that it is directly related to the atomic distribution inside them. The denser the atomic arrangement, the greater the hardness of the material.

*Why is only the surface of the water frozen?
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When the weather is cold and freezing, if the temperature is low enough, a thick layer of ice will form on the surface of the lake, but under the ice, there is still a large part of the lake that is not frozen. Why is this?Why does only surface water turn into ice?
The reason for this is mainly because the density of water will change with temperature, but this change has neither positive correlation nor negative correlation, but is similar to a parabola.

When the temperature is close to 4°C, the density of water will reach a maximum value, which is 1 g/cubic centimeter as we usually know.But when the temperature is lower or higher than 3.980°C, the density of water will decrease, and the change in density is very small, so small that we can hardly notice it, but just like the butterfly effect, this small gap may also cause very big impact.

For example, the water surface freezes, but the water below remains liquid, which is inseparable from the change in water density.

When the water temperature gradually decreases to 3.980°C, the temperature on the water surface decreases first, and their density increases accordingly.

When the density of the water in the upper layer becomes higher, it will slowly sink to the bottom of the water. The density of the water in the bottom layer is relatively low, so it starts to float up.In this way, convection is formed.

If the temperature continues to drop below 3.980°C, the lower the water temperature is, the smaller their density will be. In this way, the water temperature on the water surface is already low, and their density is also small, so the water with low water temperature can only stay on the water surface. On the surface, and the convective movement is gone, the only way for them to conduct heat is conduction. To transfer heat through conduction is to cool down in disguise, so the water temperature on the water surface is getting lower and lower. When the temperature reaches 0°C, the water will It's starting to freeze.

At this time, the water with the highest density still sinks in the bottom layer, and their temperature is also 3.980°C, which has not reached the freezing point, so it will not freeze.

The final word: If the water freezes in pieces as soon as it freezes, then all kinds of creatures in the water will have no way out in winter.Perhaps it is precisely because of this characteristic of water that so many aquatic animals have survived to this day.

*Which one is easier to fry when heated, a thin glass or a thick glass?
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Interesting: ★★★

In the cold winter, being able to hold a cup of hot water is really comfortable.But if you use a glass to hold hot water, it is likely to cause the water glass to burst, but is it easier to fry a thin cup, or is it easier to fry a thick cup?

Most people should think that the thin cup must be fried first. After all, the cup is relatively thin, and it is the weaker one no matter how you look at it.

But the fact is not what we think. Compared with thin glass, thick glass is easier to fry.The reason for such a contrast actually has a lot to do with the heat transfer coefficient of the glass.

The small heat transfer coefficient of glass also means that glass transfers heat very slowly.If hot water is poured into the glass, the inner wall of the glass will touch the hot water first, and the temperature will rise sharply.However, due to the small heat transfer coefficient, the outer wall of the glass can feel the heat after a long delay.

There is a time difference in the middle, and the thicker the glass, the greater the time difference.Under the action of thermal expansion and contraction, the inner wall of the glass with high temperature begins to expand first.But the outer wall of the glass has not absorbed enough heat, and it may still be maintained at the original temperature.The expansion coefficients of the inner and outer walls are not equal, causing the glass to burst.

The greater the difference in expansion coefficient, the greater the probability of the glass bursting, so the thicker the glass, the easier it is to burst, because the heat transfer is too slow and the temperature difference between the inner and outer walls is too large.

The final word: Thin cups have low glass thickness, relatively uniform heat transfer, and the probability of bursting is much smaller than that of thick cups.

* Is the more foam, the stronger the cleaning power?

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Whether it is washing clothes or washing dishes, there will be a lot of foam. If there is no foam, I always feel uneasy and not clean. Is there really a relationship between the amount of foam and the cleaning ability?

In fact, when we use various detergents to remove stains, it is not the foam that plays a role, but the surfactant in the detergent.It can be said that the foam is just an accessory, and has no direct connection with the cleaning ability of the detergent.

What are surfactants?As the name suggests, it is something that can make the surface of the liquid more "dynamic".Surfactants break down the tension on the surface of a liquid.

For example, when we gently drop a drop of water on the table, the drop will still maintain a "ball" shape, and the water droplets will gather in a small area and will not flow away. This is the effect of the surface tension of the liquid.

But the biggest role of surfactants is to break this tension.After adding a surfactant to the water, the water will "spread" in a large area, fully penetrate into the dirt, and trap all the dirt inside.Then as long as you rinse with clean water, you can wash away the water wrapped in dirt.

When the surfactant is working, it will produce a certain amount of foam, but these foams have no effect on the "working ability" of the surfactant.

Some surfactants produce a lot of foam when they work, but there are also surfactants with a small foam production, but this does not mean that their "working ability" is low.

The final word: The decontamination ability of the detergent depends only on the surfactant, and has no direct relationship with the foam.Foam is only an accessory produced when surfactants work, and does not reflect the detergency of surfactants.

* How harmful is the radiation hazard of fluorescent materials?

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If you go to an idol's concert, fluorescent sticks are an indispensable standard equipment, but there are rumors that fluorescent materials such as fluorescent sticks have a certain amount of radiation on the human body, it is better to avoid contact with them. How strong is the radiation of fluorescent materials? ?

The reason why fluorescent materials can emit light is that they have been irradiated by electron beams or rays during the production process. After some materials have been treated in this way, they will absorb part of the light energy and emit a visible light, which then becomes familiar to us. fluorescent material.

There are probably several types of fluorescent materials that we usually come into contact with:

The first is the luminous paint that can emit light at night. Some paints have added radioactive substances during the production process, so there will indeed be a certain amount of radiation, but it must be judged according to the composition of the paint.

The second type is the various signs seen on the road. Most of these fluorescent materials have no radiation, and the specific composition depends on the composition.

The third type is the fluorescent sticks that everyone is more concerned about. The reason why they glow is because of the fluorescent dye contained in the fluorescent sticks. This kind of thing is not radioactive and does not harm the human body.However, the liquid in the glow stick is irritating to the skin, so try to avoid direct contact.

Fourth, in fact, the A4 paper we usually use may also have fluorescent agents added, because this can make the paper look whiter.This kind also has no radiation, as long as the paper is not eaten into the stomach, it will not harm the human body.

Finally, there are fluorescent lamps. The main reason for the glow of fluorescent lamps is the phosphorus in the lamp tube. Phosphorus can emit fluorescence after absorbing ultraviolet rays, and it has nothing to do with radiation.

The final word: Common fluorescent materials are not radioactive, but some manufacturers add radioactive substances to the materials in order to create a fluorescent effect, but the probability of this is very small, and generally regular manufacturers will not do this.

* High altitude radiation can cause cancer, is it true?

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"You can't fly often! If you fly too much, you will get a lot of high-altitude radiation. After a long time, you will get cancer!" Seeing this news, it is estimated that many people who often travel by plane have to worry. High-altitude radiation is really so serious. is it serious?
The air at high altitude is thin, and without the barrier of air, the intensity of radiation will be greatly increased, which will directly affect the health of the human body, and even cause cancer in serious cases. This sounds logical, but it is not the case.

If it is true as the news said, wouldn't the captains and flight attendants who work on the plane every day be in danger?

It is an undoubted fact that the radiation in the sky is stronger than that on the ground, but it is not so strong that it needs to be so worrying.

Even if we don’t fly, we are exposed to ionizing radiation from every corner every day. There are many radioactive minerals in the ground under our feet, and there are rays from the universe in the air. Even the food we depend on has There is some ionizing radiation.As long as we live on Earth, we will be exposed to ionizing radiation all the time.Some research institutions have done related investigations, and adults will absorb about 2.4mSv of radiation a year.Among them, the proportion of cosmic rays that everyone thinks will be greatly increased in flight accounts for less than 1/10.

According to data from the National Oceanic and Atmospheric Administration of the United States, the radiation at an altitude of 2.44 meters is about 300 times higher than that on the ground. Two hundred times as much.

Although this multiple of increase sounds scary, in fact the specific value is still very small, completely within the radiation range that the human body can accept.According to the radiation safety value published by the International Commission on Radiation Protection, it is very safe to receive radiation below 20mSv every year.

Even professional doctors who are often exposed to strong radiation X-rays receive a yearly dose of radiation within a controllable range, let alone a high-altitude flight that can only add a few tenths of mSv?

The final word: The radiation in the high altitude is indeed stronger than the ground, but it is not as scary as the rumors. Flying a few times a year does not increase the risk of cancer.

*Can a human voice really shatter glass?

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We probably all know a thing or two about the allusion of "Hedong Lion's Roar", but some people have practiced the lion's roar to the point of proficiency, and can even shatter glass. Is this just for show or really strong?

In theory, a human voice can indeed shatter glass.Everything in the world has a vibration frequency, and glass is of course no exception.If the frequency of the human voice is exactly the same as that of the glass, the sound waves emitted by the human will drive the surrounding air to vibrate together, and the glass will also vibrate accordingly, and the two will reach a state of "resonance".

Glass in this case will increase the magnitude of the shock.When the amplitude of the vibration exceeds the limit value that the glass can withstand, the glass will shatter.

If the human voice is loud enough, it can indeed make the glass vibrate, but it is still very difficult to break the glass, because the breaking of the glass does not only depend on the vibration frequency, but also has a very critical relationship with the defects inside the glass. .

If there are cracks or breaks inside the glass, their "pressure resistance" ability will be greatly reduced. Although sometimes human eyes cannot capture these small "defects", this is another key to broken glass factor.

The final word: If the human voice can match the vibration frequency of the glass, the sound waves emitted by the human will drive the surrounding air to vibrate together, thereby prompting the glass to vibrate accordingly. If the glass has defects such as cracks, the probability of glass breaking will increase greatly. .

*Is it true that unusual behavior of animals can predict earthquakes?

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On the eve of an earthquake, many animals often exhibit abnormal behavior collectively. Over time, many people think that the abnormal behavior of animals may indicate that an earthquake is coming. Is this really the case?

In fact, the abnormal behavior of animals should be a necessary and insufficient condition for an earthquake to occur, that is, if an earthquake occurs, animals will have abnormal behaviors, but it does not mean that an earthquake will occur once an animal has abnormal behavior.

There is indeed a correlation between earthquakes and abnormal behavior of animals. During several large earthquakes in the 19s, animals became abnormal before each earthquake. This is called "macroscopic anomaly".

Because before a major earthquake comes, the magnetic field and gravity water level near the epicenter may be abnormal, and generally there will be small earthquakes to "step on the spot" first. Some animals can perceive these relatively small earthquakes, so they start from their own The nest escaped, accompanied by various abnormal phenomena.

But it is not only earthquakes that make animals abnormal. For example, dogs can hear ultrasonic waves, whales can hear infrasound waves, and vipers can feel infrared rays. These are things that humans cannot feel. If there are abnormalities in these, even It is not caused by earthquakes, and these sensitive animals will also appear abnormal.

Climate reasons and life cycle may cause animals to become abnormal, not necessarily related to earthquakes.

The final word: The reasons why animals become abnormal are complex, and earthquakes are just one of them. The two are correlated, but not causal.

(End of this chapter)