The rearview mirror outside the driver's cab is a convex mirror.
Using the divergent function of convex mirror to light, as well as the characteristics of upright, narrow and virtual image, the objects you see are small and the observation range is wider, thus ensuring driving safety.
Another example is as follows:
Spiced tea eggs are very popular with people, especially when it is hot. Careful people will find that when the eggs are just taken out of the boiling gravy, if they are eager to shell and eat them, it is inevitable to peel them off with the "meat". To solve this problem, there is a trick, that is, soak the eggs just out of the pot in cold water for a while, and then peel them, so that the eggshells can be peeled easily.
General substances (with a few exceptions) have the characteristics of thermal expansion and cold contraction. However, when different substances are heated or cooled, the speed and amplitude of expansion and contraction are different. Generally speaking, substances with low density are easier to expand and contract than substances with high density, and substances with fast heat transfer are easier to expand and contract than substances with slow heat transfer. An egg consists of a hard shell, a soft protein and a yolk, and their expansion and contraction are different. When the temperature changes slightly or slowly and evenly, nothing can be displayed; Once the temperature changes dramatically, the expansion and contraction speeds of eggshells and protein are inconsistent. When the boiled egg is immediately immersed in cold water, the temperature of the eggshell will decrease and shrink rapidly, while protein is still at its original temperature and does not shrink. At this time, a small part of protein will be squeezed into the short position of the egg by the eggshell. Then, due to the decrease of temperature, protein gradually contracted. By this time, the contraction of the eggshell was already very slow, and protein was separated from the eggshell. Therefore, when peeling, the shell and the "meat" will not come off together.
It is very useful for us to understand this truth. If all things that need to undergo great temperature changes are made of two different materials together, their thermal expansion performance must be considered when selecting materials, and the closer they are, the better. Reinforced concrete is widely used when engineers design houses and bridges. Because the expansion degree of steel bars and concrete is similar. Although the temperature is different in spring, summer, autumn and winter, it will not produce harmful forces, so reinforced concrete buildings are very strong.
In addition, some electrical components are made of two metals with very different thermal expansion characteristics. For example, the thermal expansion of copper sheet is greater than that of iron sheet, and the bimetal nailed together by copper sheet and iron sheet will bend due to different expansion degrees when heated under the same conditions. Using this characteristic, many automatic control devices and instruments have been manufactured. There is a small bimetal in the "starter" of the fluorescent lamp, which can automatically expand and contract with the change of temperature, thus playing the role of automatically turning on the fluorescent lamp.
There are countless examples of this. Physics is a practical science, which is closely related to industrial and agricultural production and daily life. Physical laws themselves are generalizations and abstractions of natural phenomena.
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, constantly increasing 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.
Today, all the amazing scientific and technological achievements of mankind, such as sheep cloning, internet, nuclear power plants, aviation technology and so on. All of them are based on the observation and research of trivial things around scientists in the early years. In learning, students should establish scientific consciousness, focus on the big picture, start with small things, experience observation, thinking, practice, innovation and other activities, gradually master scientific learning methods and train scientific thinking methods, and soon you will have the mind of a scientist, laying a solid foundation for your amazing development and beautiful life in the future.