Physics in life 600 composition 1:
(1) Why can ultraviolet rays kill bacteria?
Ultraviolet light is an invisible light wave that exists outside the ultraviolet end of the spectrum, so it is called ultraviolet light. According to different wavelength ranges, it is divided into three bands: A, B and C. Among them, the wavelength of C-band ultraviolet light is between 240 and 260 nm, which is the most effective sterilization band, and the strongest wavelength point in the band is 253.7nm. Modern ultraviolet disinfection technology is based on modern epidemic prevention, optics, biology and physical chemistry. It uses a specially designed C-band ultraviolet generator with high efficiency, high intensity and long life to generate strong ultraviolet C light to irradiate water. When all kinds of bacteria, viruses, parasites, algae and other pathogens in water, air and the surface of objects are irradiated by a certain dose of ultraviolet C light, the dna structure in their cells is destroyed, so
(2) Why should we prevent ultraviolet rays?
In recent years, a large number of halogen-containing compounds, such as freon, remain over the earth, which are decomposed by ultraviolet rays to generate active chlorine, and then react with ozone to destroy the ozone layer, making short-wave ultraviolet rays possible.
Reach the ground. Long-term exposure to ultraviolet rays will bring different degrees of harm to human body, such as increasing the number of cataract patients, reducing human immune function and hindering the growth and development of plants and marine animals. Therefore, people have developed a kind of fiber to prevent ultraviolet rays from penetrating, commonly known as? Ultraviolet resistant fiber? The fabric woven with this fiber has the function of preventing ultraviolet rays, which can prevent people who work in the field for a long time in summer, such as soldiers, traffic police, geologists, construction workers and so on. Wear clothes made of this fabric. The automobile interior cloth made of ultraviolet resistant fiber can reduce the fading caused by ultraviolet radiation and prolong the aging time.
(3) In ancient wars, why did soldiers sleep on the ground with quiver?
As we all know, sound travels much faster in solid than in air. The speed of sound in the air is about 340m/s, while the speed of sound in the solid is above1000 m/s. At night, the sound of cavalry marching is generally less than 2,000m, so it only takes a few seconds to know from the earth that the sound of the opposing army marching is faster than that in the air. This is not the main reason why soldiers slept with quiver in ancient wars.
The reason why soldiers sleep with quiver is to consider two points from the propagation of quiver and sound in the earth:
1. When horses and soldiers are marching on the road, it is much farther for people to lie on the ground than to hear the sound of marching from the air. The author has done such an experiment. Take a piece of wood 6 meters long. A is at one end of the wood and B is at the other end. A taps the wood with his finger and adjusts the strength of his finger so that B can just hear it from the air at the other end. At this time, if B gets down and puts his ear close to the wood, A still beats the wood with his original strength. A The loudness of the sound heard is much louder than that heard from the air. It shows that the sound generated by knocking on a solid travels farther directly from the solid than from the air, so soldiers can hear the sound of troops marching farther away through the earth, so that soldiers can find the enemy's marching action earlier.
2. Analysis from rocket launchers. Let's first look at the tuning fork and the * * * sound box in the acoustic experiment. When doing the sound experiment, it is best to align the mouths of two sound boxes. * * The sound box plays the role of collecting sound waves, so does our auricle. Let's analyze the ancient rocket launcher. It is made of leather, which is very hard and strong after drying. Rocket launchers on the ground also play a role in collecting sound waves. The same sound source emits sound in the same place. At a proper distance from the sound source, the sound heard on the quiver is louder than that heard in the air. I have done such an experiment. There are two independent houses separated by a wall, but there are no doors and windows on the wall. We are in this room, and there is a lot of noise next door, so we can't hear clearly here. If you take a porcelain jar, put the bottom close to the walls of two rooms and put your ear close to the mouth of the jar, you can clearly hear the sound next door. It shows that the cylinder also plays a role in collecting sound waves. From this point of view, soldiers can hear the noise coming from a distance when sleeping with their quiver on their pillow, and they can find out the enemy's situation as soon as possible.
There is learning everywhere in life.
Physics in Life 600 Papers 2:
Friction phenomenon in life
Last Sunday, my cousin came to my house, looking very proud, and I didn't know what medicine she was selling. After dinner, my cousin said, Sunny, these two books can't be put together separately. Can you believe it? Stop bragging! The two books are not bonded. How can they be inseparable? If you don't believe me, let's try! ?
I saw my cousin holding a book in one hand, turning a page and inserting a page. In a short time, the two books were stacked together. Cousin, let me try. I thought it was not easy, so I picked up the book and touched it gently, but it didn't move. Now I'm angry, sucking milk desperately, and the book is still there? Without a scratch? . Cousin smiled and said:? Do you want me to help you? As she spoke, she picked up the book, and we both retreated like tug-of-war, but the more we pulled, the harder the book became. Hug? The tighter you hold it. I froze. What's going on here? Do you want to know? Cousin asked. I nodded hard.
My cousin showed me two things, one is a big wheel and the other is rubber-soled shoes. Cousin said:? On muddy roads or snow, in order to avoid wheel slipping, it is necessary to increase the friction between the wheel and the ground. The general method is to rough the contact surface, sprinkle sand or cinder on the ground, or wrap a chain around the wheel of the car. The pattern on rubber-soled shoes is also specially designed to increase friction and avoid slipping. ? oh ? I see, it turns out that everything is just friction! The more overlap, the greater the friction, which is why I can't open these two books. Friction is amazing!
Physics in life 600 papers 3:
How was Flying Monkey King made? The Journey to the West is a well-known and deeply loved TV series, in which the Monkey King left a good impression, but thoughtful viewers will definitely ask, the Monkey King's? Walking in the clouds? How was it filmed? Let's talk about this problem. We know that at ordinary times, what we call motion and stillness are relative, which is relative to the reference object we assume to be motionless. If we sit in a closed train car, we won't know whether the train is stationary or moving at a constant speed. Only by opening the curtains and seeing the reference objects such as trees and villages beside the railway tracks can we judge whether their positions have changed. Using the relativity of motion, you can shoot the Monkey King's? Walking in the clouds? The camera is off. Like the Monkey King? Is Yun Teng far away? The Monkey King's action shot and scenery shot were taken first, and then two sets of pictures were put in? Stunt machine? When overlapping, the white clouds and mountains, rivers, lakes and seas in the background move rapidly as reference objects and are photographed with a camera. When watching TV, the audience takes white clouds, mountains, rivers, lakes and seas as the reference objects, thus producing? Is Yun Teng far away? Effect.
Why are there strips on the back window of the car? In winter, the temperature difference between the inside and outside of the car is relatively large, which is hot inside and cold outside. The water vapor emitted from the people sitting in the car often condenses on the window glass, forming a layer of frost. So you can't see the scenery outside the car clearly. But drivers need to know the situation behind the car at any time when driving and reversing. What do we do? People make the rear window glass of a car into a double layer, and a film is stuck inside, and there are resistance wires on the film. After the resistance wire is electrified, the frosted flowers condensed on the glass will melt and evaporate with the increase of glass temperature. Therefore, the thin strip on the back window of the car is actually a special electric heater. With it, even if the weather is cold again, you can look back from the car and see the scenery outside at a glance.
Do you need electricity to do EEG? In order to diagnose patients' brain diseases, doctors often give patients EEG. Is it necessary to electrify the brain when doing EEG? Actually, it is not. It turns out that the brain itself can generate electricity like a generator, but the voltage generated is too weak, only about 1 microvolt, which is difficult to measure. Therefore, when doing EEG, doctors always use brain motor to amplify the patient's brain voltage by more than one million times, which is about 1 volt, which is close to the voltage of dry battery, and then draw the amplified brain voltage on recording paper to get the brain voltage curve, which is called EEG.
Will it change? Weight? Students who have studied physics may know that the weight of the object itself is not static, that is, sometimes? Weightlessness? ; Sometimes? Overweight? . What causes the change in the weight of an object? Don't worry, let's look at the following story first: once upon a time, there was a story: a businessman bought 5000 tons of herring from a Dutch fisherman and shipped it from a Dutch city to an African city near the equator? Go to the port of maga. When I got there, I weighed it and found that the herring was nearly 19 tons short. Strange! Where did it go? It can't be stolen because the ship didn't call all the way. At that time, no one could reveal the secret, but now we finally know the reason: it turned out that this was a joke played by gravity. Because the earth is slightly oval, its radius of north and south poles is 20 kilometers smaller than that of equator. The smaller the radius, the greater the attraction; Or conversely, Dallas goes to the auditorium. Therefore, when 5000 tons of Dutch herring are transported near the equator, the weight of herring naturally changes? Light? Yes In addition, the weight of the object changes a lot! If you are on a high mountain, it is lighter than on the flat ground; The equator is lighter than the poles; It is much lighter in water than on land, and so on. As you can imagine, if you fly to a high altitude area where the gravity of the earth can't reach, there is no weight at all, because the gravity of the earth is very small. However, no matter how it changes, the quality of the object will not change!
Well, now everyone knows the truth! In fact, there are many similar problems around us. As long as we can find it in time and combine it with theory, we can find the correct answer. I believe that when you encounter similar problems in the future, don't? Nothing to do? Oh!