Physics

This article explains why it is necessary to put a large number of stones in the wok when roasting chestnuts, peanuts, or sunflower seeds. By explaining the heat transfer process of roasting chestnuts, it analyzes the fundamental reason why the chestnut shells easily char and catch fire while the kernels are not cooked when roasting directly in an iron wok. It also demonstrates the heat transfer effect of the stones and the help of stirring the stones in achieving uniform heating and improving the heat transfer efficiency.

This article addresses the question of why standing barefoot on tiles feels cooler than standing on a quilt, introduces the concepts of heat conduction and thermal conductivity, and explains that the thermal conductivity of tiles is much higher than that of quilts at the same temperature, allowing them to dissipate heat from the skin more quickly. It also discusses the differences in thermal conductivity among various materials, the factors that influence it, and its practical applications.

This article explains why boiling water does not necessarily reach 100°C, stating that the boiling point of water at standard atmospheric pressure is 100°C. The boiling point of water changes with changes in atmospheric pressure—the lower the atmospheric pressure, the lower the boiling point; the higher the atmospheric pressure, the higher the boiling point. It also cites examples of the low boiling point of water in high-altitude regions and the use of pressure cookers to increase atmospheric pressure and raise the boiling point.

This article focuses on the phenomenon of water droplets appearing on beverage bottles taken out of the refrigerator in summer, introduces the concepts of humid air and saturated air, as well as the relationship between saturated moisture content and temperature, explains that this phenomenon is the condensation of water vapor after the humid air around the beverage bottle reaches saturation when it is cooled, and also explains the reason why the bottle wall will form frost when the beverage in the bottle freezes

This article focuses on the question of "why ice skates are equipped with ice blades", introducing the development history of ice skates, explaining that the reason why ice blades can provide forward momentum during the start and acceleration phases, reduce sliding friction, and maintain stability is that there is a lubricating water film between the ice blade and the ice surface. It also describes the contribution differences of the three mechanisms (high pressure melting, friction heating, and liquid film on the ice surface) in forming the water film at different temperatures.

This article focuses on the question of "why opening the refrigerator door cannot cool down the indoor temperature". It introduces the basic structure of the refrigerator, the types of refrigerants, and the working principle of refrigeration, explaining that the heat released by the condenser is equal to the heat absorbed by the evaporator plus the heat converted by electrical energy. Therefore, opening the refrigerator door not only fails to reduce the indoor temperature, but will also cause the indoor temperature to rise due to the continuous operation of the refrigerator, producing more heat. It is recommended to use the refrigerator to cool drinks and food in summer.

This article focuses on the problem of bicycle tire bursts under summer sun exposure, introduces the characteristics of thermal expansion and contraction and related phenomena in daily life, explains the microscopic nature of gas thermal expansion and contraction and the principle of tire bursts, demonstrates the methods of preventing tire bursts in summer, and lists examples of the application of the principle of thermal expansion and contraction in daily life.

This article takes the phenomenon that ink drops spread out when they fall into water as the entry point, introduces the definition of molecular thermal motion and diffusion examples of the three states of matter (solid, liquid, and gas), and explains the discovery process, manifestation, generation principle, research history, and important scientific significance of Brownian motion in the fields of molecular motion theory and statistical mechanics

This article focuses on why some Africans are accustomed to balancing large pots on their heads, and introduces the relevant research of scientists. It points out that this method of carrying has the advantages of a large bearing area and low pressure in mechanical structure, high friction to prevent objects from slipping, and the gravity axis coinciding with the human body to reduce the effort of muscle balance. Moreover, it has a higher energy utilization efficiency. When the weight carried on the head does not exceed 20% of one's own body weight, the energy consumed is similar to that when no weight is carried. At the same time, it reminds teenagers that their skeletons are not yet fully developed, so they should not try to carry heavy objects on their heads. The whole society should pay attention to the growth of teenagers and reduce the burden on their shoulders.

This article explains the principle of discontinuous dripping from a leaky faucet, namely, the surface tension of the liquid will hold the water leaking from the faucet, and the water will only fall when it accumulates to a level that the surface tension can no longer support. Therefore, the dripping water is discontinuous. It also points out that this phenomenon only exists in environments with gravity, and lists similar water accumulation and release phenomena such as water discharge from public toilet tanks.

This article focuses on the question of "why the cross-section of most animal bones is hollow and ring-shaped", explaining the mechanical principle that animal bones are hollow because they mainly bear bending and pressure, with most stress concentrated at the edges. At the same time, it introduces the application of this principle in the structure of plant stems, as well as in production and daily life fields such as pipe materials and arched buildings.

This article focuses on the issue of "internal injuries" caused by potato falls, and combines the phenomenon that potatoes, apples, pears, and other fruits and vegetables appear to be intact on the surface but have brown and rotten interiors in daily life. It uses the principle of mechanical contact to explain that the maximum shear stress of an elastic sphere when it is compressed is located about 47% of the radius from the surface, rather than the contact surface. It points out that improving packaging and transportation conditions is the fundamental way to avoid potato internal injuries, and mentions that the internal injuries caused by the imperial torture in the Ming Dynasty, which did not leave obvious external injuries, also conform to the same mechanical laws.