Physics

This article focuses on the phenomenon that the whistle of a train becomes sharper when it approaches and quieter when it moves away, and introduces the origin of the discovery of the Doppler effect, its working principle, the Mach number parameter that affects its intensity, and the application of this effect in fields such as traffic speed measurement and medical blood flow detection.

This article focuses on the question of "why ants can fall from a height without getting hurt", and, based on the relevant principles of air resistance, explains the reasons why ants can fall from a height without getting hurt: air resistance can easily balance with the ant's gravity, making its falling speed slow; it suffers less impact from the ground; and since ants are small in size and have relatively high physical strength, the ground's impact force does little harm to them.

This article combines the event of Ko Shuangliang, who was honored as "the first flying man in Asia", driving a car to fly over the Hukou Waterfall of the Yellow River in 1997. It explains the principle of how a car can fly over the Yellow River from the perspective of the mechanics of inclined throwing, introduces the preparatory measures and safety design for the flight, and points out that the success of the flight also requires the performer to have excellent skills and great courage.

This article focuses on the issue that heavier slabs are actually safer in the "crushing a large stone on one's chest" performance, introduces the common forms and related cases of this acrobatic performance, explains the physical principles and other safety measures involved, and reminds non-professionals not to attempt it lightly.

This article focuses on the reason why geckos can climb on smooth walls, introduces the process of excluding past related hypotheses, and points out that geckos mainly rely on the Van der Waals force between the bristles on their feet and the surface of objects to achieve adhesion. Their rapid movement is related to the rapid formation and disappearance of the Van der Waals force. In addition, the adjustment of the angle of the bristles, muscle and nerve regulation, and capillary action also have an impact on their adhesion and climbing. At the same time, it mentions that there are still many mysteries of gecko feet that have not been unraveled, and that there are problems such as mutual adhesion and difficulty in converting between adhesion and detachment in current artificial bristle imitations.

This article takes Adili, a tightrope walker who is renowned as the "High-altitude Prince" of China, as an example to explain, from a mechanical perspective, why tightrope walkers hold long poles. That is, by adjusting the position of the long pole to adjust the center of gravity, the line of human gravity always passes through the supporting surface of the tightrope, thus maintaining body balance.

This article focuses on the topic of "why singing can shatter glass". Through the cases of Vitas breaking the crystal chandelier on the roof of the Kremlin during his performance and Naomi Watts shattering the glass on the hotel balcony with her screams, it explains the reason why high-pitched singing can shatter glass based on the physical principle of resonance, and introduces the definition of resonance, the factors affecting the natural vibration frequency of objects, and the relevant conditions under which glass can be shattered by singing.

This article focuses on the question of why a jack can lift a car, introduces the principles of slope-based force saving and self-locking, explains the working mechanism of mechanical jacks that use a spirally coiled slope combined with the lever principle to generate large lifting force, and also mentions that hydraulic jacks use hydraulic transmission principles. It demonstrates that the working principles of different types of jacks are basically the same.

This article focuses on the question of whether the water flow in toilets in the Northern Hemisphere always rotates counterclockwise. It introduces the definition and principle of the Coriolis force (Earth's rotational force), points out that the Coriolis force effect is weak on a small scale, and the direction of the toilet vortex is mainly determined by its own structure. At the same time, it elaborates on the significant role of the Coriolis force in large-scale and long-term processes such as river erosion, railroad wear, and typhoon structure

This article focuses on the question of "why running the same distance is more exhausting than cycling". Through semi-quantitative physical estimates and exercise physiological measurements, the article analyzes aspects such as overcoming external dissipative forces, the energy consumption of the vertical movement of the center of gravity during running, and overcoming internal friction forces. It explains why cycling is much more energy-efficient than running over the same distance.

This article focuses on the issue of why a unicycle with a high center of gravity can stand upright without falling over. It explains the principle that relies on the driver controlling the pedals to generate ground friction torque to balance the overturning torque, and introduces the structure and application of the Segway (a powered scooter) based on the same balancing principle and using an automatic control system.

This article focuses on answering the question of "why is it harder to ride a bicycle with underinflated tires?" It points out that the reason why cycling is more difficult is not because of increased friction (friction is unrelated to the contact area, and the friction force of the bicycle's rear wheel is forward, which should make cycling easier). The real reason is that after the tire is deflated, the point of support on the ground and the point of gravity are separated. The torque generated by gravity will "resist" the torque generated by the chain, resulting in harder cycling, and the more deflated the tire is, the harder it is to ride the bicycle.