Physics

This article discusses why there are no diving competitions from heights above 10 meters in competitive sports. It introduces the classification of diving events and height settings, explains that the impact force upon entering the water will increase sharply with the height of the dive due to the "liquid toughening" phenomenon, and that 10 meters is the scientifically verified and practically proven maximum safe height for competitive diving. It also states that diving from higher heights belongs to extreme sports in high altitude rather than competitive sports events.

This article focuses on the question of "why the violin can play beautiful music", and elaborates on the composition of musical sounds and the principles of determining pitch and timbre. It explains the mechanism of the violin's complex vibration and sound production, the resonance effect of the sound box, as well as factors such as string tension, the quality of the bridge, bowing technique, and the performer's skills, to explain why the violin can produce beautiful music.

This article focuses on the question of "why do wound-up clocks and watches accurately keep time", introducing the discovery of the isochronism of pendulums, the working principle and application history of escapement mechanisms, and explaining the reason why wound-up clocks and watches can accurately keep time based on the laws of conservation of work and energy in physics.

This article explains the structure and mechanical principles of the freely rotating wheels of supermarket shopping carts, and compares them with the relevant design of bicycle forks to illustrate the important role of the position of the rotating axis in ensuring the stability of the movement.

This article focuses on the question of "why both shuttlecocks and badminton rackets are equipped with feathers", introducing the history of shuttlecocks, their manufacturing methods, and various kicking techniques. It explains the principle that feathers can generate torque through air resistance to keep the shuttlecock stable with its base facing downward. At the same time, it demonstrates that badminton rackets and arrows also utilize the aerodynamic effect of hard feathers to achieve flight stability. This aerodynamic stabilization principle is also applied to tail-fin weapons in modern warfare.

This article takes the theme of "Why lotus leaves grow out of mud without being stained", first cites the ancient poems and articles of Wei Yingwu and Zhou Dunyi to illustrate the cultural implication of lotus leaves, then introduces the research findings of German scholars, explains the principle that the micro-nano structure and wax-like protrusions on the surface of lotus leaves can make droplets carry pollutants and achieve self-cleaning, and finally mentions the characteristics of super-hydrophobic surfaces, similar structures in nature, and related bionic research and application results.

This article focuses on the question of "why soap water can blow bubbles while ordinary water cannot", introducing the definition of surface tension of liquids and related phenomena. Through experimental comparison, it demonstrates that the surface tension of soap water is lower than that of pure water, and explains the principle that soap dissolved in water reduces the surface tension of water, making it easier to blow bubbles.

This article focuses on the question of "why geese flying in a line can save energy", and introduces the formation of geese flying in a line during migration. Combined with the principle of induced vortices in aircraft flight, it explains why geese flying in a line can save energy, and at the same time, it shows that the lead goose flies the hardest, and the geese will take turns to replace the lead goose to ensure that all members reach their destination.

This article focuses on the question of "why golf balls are covered with small dimples", and introduces the development and evolution of golf balls. Combined with related concepts in fluid mechanics such as ideal fluids, d'Alembert's paradox, and boundary layer separation, it explains the principle that the "pitted" golf balls with small dimples on their surfaces can reduce the drag caused by the pressure difference between the front and back sides by delaying the boundary layer separation point and reducing the vortex zone, thus flying farther than smooth golf balls.

This article focuses on the issue of setting up safety lines in subway stations. By recounting the tragic incident at the Olonets Station in Russia in 1905, it uses Bernoulli's principle to explain the reason for setting up safety yellow lines on platforms, namely to prevent the pressure difference generated by high-speed trains from pushing people towards the trains and to ensure the safety of waiting passengers.

This article explains the reasons why foam occurs when opening a beer bottle: Beer is a supersaturated solution containing carbon dioxide. After opening the bottle, the pressure is reduced so that carbon dioxide escapes and forms bubbles; at the same time, polypeptides and proteins contained in malt and other ingredients in beer can be used as surfactants to stabilize bubbles. Due to this kind of substance, beer forms a rich and stable foam, which is relatively easy to burst compared with cola foam.

This article explains the principle that tree roots send water to treetops, explains the osmotic pressure phenomenon through U-shaped tube semi-permeable membrane experiment, introduces the selectivity of semi-permeable membrane, mentions Nolay's early experiments and Van Thoff's 1877 quantitative study on osmotic pressure, pointing out that root osmotic pressure combined with transpiration and capillarity can transport water to the treetops tens of meters high.