1. Silent World Silent World Imagine what a silent world would be like in our colorful world. Sound plays an important role. What would the world be like without sound? Let's imagine what kind of world it would be. Is it interesting? Cold? Quiet? Or ... man is the master of the world. What effect will sound have on human beings first? Then let's talk about the influence of sound on human beings first! What will happen to human beings if there is no sound? If there is no sound, people can't make a sound when they speak, just like people who lose their voices speak in sign language. Why do people need ears? There is no sound to listen to. Is it for decoration? How can there be such beautiful music now? If there is no sound, what is the point of the whole world dying in a dead universe? If there is no sound, how can students study and read at school? How can there be music, English, information ... courses? How will you express what you want to express? Do you rely on sign language? I really can't imagine what teaching would be like at that time. Pangu, the ancestor of China, created human beings because he thought that the world was too quiet and lifeless. Now, if there was no sound, there would be no laughter. Then why are there humans? What's the point of having humans? We are not Beethoven, nor do we have Beethoven's skills. Even if we can't hear, we can bite a stick with our teeth and feel the sound according to the vibrating skull. But if there is no sound, not even sound waves, even Beethoven can't feel the sound, let alone play the piano. If there is no sound, how can there be a telephone now? If relatives are far away, how will they talk? Can you sign language after such a long distance? If … if … if too much, I think these ifs are impossible. In short, human beings need sound. It's hard to imagine how human beings would survive without sound! Of course, this is not just human beings; Animals also need sound, and even animals can't live without sound; For example! Bats can be said to be a special kind of animals. Although it has a pair of eyes, it can always see if it can't hear, but do you know it is called "blind" in the animal kingdom? Its eyes are not worthy of the name, because it relies on its ears. Listen to ultrasonic waves with your ears to identify positions and avoid obstacles. If there is no sound, the bat can't hear the sound, can't catch the food and can't fly, then does it still have a chance to survive? Of course, bats are not the only animals, and other animals cannot do without sound. Here is an example to emphasize that "the earth cannot live without sound". Without sound, people seem to live in a vacuum, quiet and silent. There is no wind, no rain, no reading, but more birds, songs and laughter. Therefore, the universe in which human beings live now has no color and no sound. 2.5. Introduce the working principle of the camera. Generally speaking, it applies the optical imaging principle to image the object on the photosensitive material through the photographic lens. The following will briefly introduce the principle of photographic optical imaging: human understanding of the nature of light, the propagation of light and the principle of lens imaging. Human understanding of the nature of light has gone through a long and tortuous process. In the whole18th century, the particle flow theory of light is still dominant in optics. It is generally believed that light is composed of tiny particles, which are emitted from point light sources and radiate in all directions in a straight line. /kloc-At the beginning of the 9th century, the works of Yang and Fresnel gradually developed into today's wave optical system. Now, the understanding of the essence of light is that light, like physical objects, is a kind of substance, which has both the properties of wave and particle (quantum), but as a whole, it is neither wave nor particle, nor a mixture of the two. In essence, light is no different from ordinary radio waves. Like electromagnetic waves, light is a shear wave, that is, the vibration direction of the wave is perpendicular to the propagation direction. Luminous body is the emission source of electromagnetic wave, and the electromagnetic wave emitted by luminous body propagates to the surrounding space, similar to the wave generated by water wave fluctuation. The distance between two points with maximum or minimum intensity is called wavelength, which is denoted by λ. The time required to propagate a wavelength is called a period, which is represented by t, and the period is the time required for a particle to complete a vibration. The number of vibrations in 1 sec is called frequency, which is expressed by nu. The distance that vibration travels through 1s is called velocity, which is represented by "v". There are the following relationships among wavelength, frequency, period and speed: v=λ/T, ν= 1/T, and v=λν. Therefore, the wavelength of light is inversely proportional to the frequency. In fact, light waves only account for a small part of the entire electromagnetic wave band. The electromagnetic wave with the wavelength of 400 ~ 700 nm can be felt by human eyes, which is called visible light. Beyond this range, the human eye will not feel it. Different wavelengths of visible light produce different color sensations in our eyes. According to the wavelength from long to short, the color of light is red, orange, yellow, green, cyan, blue and purple. The propagation speed of electromagnetic waves with different wavelengths in vacuum is exactly the same, and the value is c = 300,000 km/s. Here are some basic laws of geometric optics-the law of light propagation: (1) The law of light propagation in a straight line in a uniform medium, that is, light is a straight line in a uniform medium. The phenomenon of linear propagation of light can be seen anytime and anywhere in daily life, such as objects turning into shadows after being irradiated by light, pinhole imaging and so on. The linear propagation of light leads to the concept of light. (2) The Law of Independent Propagation of Light The propagation of light is independent. When different rays pass through a certain point in the medium from different directions, they do not affect each other. When two rays converge at a certain point in space, its function is simply superposition. This characteristic of light makes the light from all points of the object enter the camera lens without affecting each other, forming an image on the imaging plane. (3) Law of Reflection of Light When light propagates to the interface of two different media, it will change the propagation direction and reflect the light. The law of light reflection points out: ① The normal lines of incident light, reflected light and the projection points of light on the interface are in the same plane, and the incident light and reflected light are located on both sides of the normal line respectively. ② The shooting angle and reflection angle are equal. The angle between the incident light and the normal n is recorded as the incident angle, which is expressed by I; The angle between the reflected light and the normal n is recorded as the reflection angle, which is expressed by α. Then i=α. The reflection of light is also reversible. If light is incident on the interface against the original reflected light, it will be reflected against the original incident light. According to different interfaces, reflection can be divided into directional reflection and diffuse reflection. Light is incident on a bright plane mirror from one direction, all incident points fall on the same plane, and all reflections are in the same direction, which is called directional reflection. When light is projected from one direction onto a rough surface (such as ground glass surface), because the rough surface can be regarded as composed of many facets with different angles, the light is reflected from different directions, which is called diffuse reflection. However, it should be noted that in the diffuse reflection phenomenon, every ray still follows the reflection law. The reflection of light plays a very important role in photography. For example, people themselves do not emit light, but when light shines on people from all angles, it can be reflected from all angles. We often use reflected light to take pictures, which is to follow the reflection law of light. 3. Physics exists around physicists. Galileo, an observant Italian physicist, took great interest in the swing of the copper chandelier hanging in the air in Pisa Cathedral when he was attending church. Later, after repeated observation and research, he invented the synchronization of the pendulum. In order to understand the essence of "God's wrath", Franklin, an American physicist who is brave in practice, risked his life to bring "God's fire" to the world with an ordinary kite on a day of lightning, thunder and rain, and invented the lightning rod. Henry Achar, a British innovative scientist, went to the post office to handle affairs. At that time, a foreigner next to me took out a large edition of new stamps to cut and post on the envelope, but he didn't have a knife. I borrowed it from Aga, and Aga didn't have it. The foreigner had a brainwave, took off the pin on the suit and tie, neatly pierced a circle of holes around the stamp, and then neatly tore it off. When the outsiders left, they left Aga with a series of profound thoughts, and therefore invented the stamp punching machine, and the stamps with tooth patterns were born. Archimedes discovered Archimedes principle in ancient Greece; German physicist roentgen discovered x-rays; ..... There are countless examples of physicists who have made great achievements in studying trivial matters around them. Physics also exists around students. After learning the basic knowledge of measurement, the students began to make soft rulers. A classmate is ingenious, wrapping the kraft paper soft ruler with transparent glue, which is more firm. Then a box wrapped in bubble gum is used as the shell of the soft ruler, the center of the box is made of iron wire, and the end of the soft ruler is fixed on the shaft, thus a tape measure that can be cleaned and reused is born. At the same time, inspired by the soft ruler, this student solved an exercise through experiments: when measuring the length of an object with a soft ruler, if the soft ruler is lengthened, is the measured value too large or too small? He did such a simulation experiment: draw a straight line on a white paper, mark it with a scale, then stick it with transparent glue, and then pull it down to make a "soft ruler". With the "soft ruler", he not only found the answer to the above questions, but also clearly saw that the graduation value became larger, and he knew why. After learning the knowledge of electricity, the students explored the maximum voltage that the earthworm can bear: when a voltage of 1.5V is applied to it, the earthworm quickly secretes mucus and struggles to jump out of the bottle. Earthworms are electrically divided into two parts when a voltage of 3V is applied. When measuring the power of "2.4V, 0.5A" small bulb and studying its luminous situation, some students are not satisfied with adding 2.4V voltage to the bulb, but do destructive experiments with their own small bulbs, and constantly increase the voltage at both ends of the bulb until the voltage reaches 9V, and the filament of the bulb burns out. When some students are learning the knowledge of evaporation, they take pains to sit at the table and observe the same two drops of water (one of which is flat), and then observe them carefully, and then analyze and compare them to get the factors that affect evaporation; ..... It is not uncommon for students to capture trivial things around them and explore. 4. Factors affecting the size of friction In human life and production, friction is everywhere. Friction can be divided into sliding friction, static friction and rolling friction according to its nature. Different friction forces have different factors that affect their magnitude. Our group chose sliding friction and static friction to study, and roughly studied the friction of objects moving in fluid. So far, some achievements have been made. First of all, for sliding friction, we know from textbooks that it is directly proportional to the positive pressure. Our team members used the control variable method to accurately verify the conclusion that the sliding friction is proportional to the positive pressure when the dynamic friction coefficient is constant through experiments. However, because the dynamic friction coefficient is difficult to control, the conclusion that sliding friction is proportional to the dynamic friction coefficient is only roughly verified under the condition of constant positive pressure. From this, we can still get the formula f = μ n. So what determines the dynamic friction coefficient? As we know, the dynamic friction coefficient reflects the roughness of the object surface, which in turn determines the dynamic friction coefficient, which is the interaction between two objects with unsmooth contact and relative motion, so the dynamic friction coefficient is not determined by the roughness of one object surface alone, but by the roughness of the contact surface of two objects with interactive friction. If we take a pen and a short piece of rope and wind the rope around the pen, we will find that the more times the rope is wound, the harder it is to pull, especially where there is overlap between the ropes. Are there any other factors that affect friction? We come to the conclusion that every time the rope wraps around the pen, there will be one more contact point between the rope and the pen, and there will be countless interactions between the two, that is, there will be more places where friction is generated. All the friction forces together increase the resultant force. If the ropes overlap, not only will there be interaction between the rope and the pen, but there will also be interaction between the rope and the rope, which will hinder each other's movement. At this time, the pressure between the rope and the pen includes not only the pressure between the rope and the pen, but also the pressure between the rope and the pen, so the friction increases sharply and it is difficult to pull the rope. In life, when ships dock, they always tie the piles to the shore with ropes, and also use the rope to wind several times to increase friction. But this does not include other factors that affect friction besides positive pressure and dynamic friction coefficient. For static friction, the reason is that there is a tendency of relative motion between objects. The reason for the trend of relative motion is external force. Therefore, the conditions of static friction include not only unsmooth contact surface and positive pressure, but also external force. Under the condition of not exceeding the maximum static friction, the greater the external force, the greater the static friction. Once the maximum static friction is exceeded, the object begins to move, and the static friction becomes sliding friction. So what is the maximum static friction related to? Experiments show that fmax=μN indicates that the maximum static friction force is directly proportional to the static friction factor and the positive pressure, and the static friction factor is slightly larger than the dynamic friction factor, because when the external force is equal to the dynamic friction force, the force on the object is still balanced, and the external force must be increased to make the object move. As for the movement of an object in a fluid, it is mainly caused by the resistance of the fluid when it displaces the fluid, but the friction of the fluid on the side of the object can not be ignored. For the resistance when discharging fluid, we can reduce it by converting the moving object into streamline, or increase it by the opposite method. As for the friction on the side when an object moves, we know that when an object moves, it will drive the nearby fluid to move together, while the fluid a little farther away is still in a static state. In this way, according to the Bernoulli equation "= constant", the static fluid will exert pressure on the object, and the contact between the object and the fluid will not be smooth, resulting in friction. Moreover, with the increase of speed, the pressure of moving fluid decreases, while the pressure of static fluid remains unchanged, so the pressure difference and pressure increase and the friction increases; Through similar analysis, it can be concluded that the friction increases with the increase of depth. The factors that affect the magnitude of friction are fixed and few, but their manifestations are very diverse and complicated. Only by fully understanding and controlling these factors can we make full use of beneficial friction, avoid harmful friction and improve production and life to the maximum extent.

Please accept it, thank you!