Physics

This article focuses on the problem that bicycles are prone to tip over when braking the front brake abruptly, and explains its principle: When the bicycle is traveling at a high speed, braking the front brake abruptly will cause the front wheel to lock, and the static friction between the front wheel and the ground will turn into sliding friction. The rolling friction of the rear wheel is much smaller than the sliding friction and can be ignored. Due to the inertia of the bicycle, when taking the bicycle as the reference frame, if the torque generated by the inertial force is equal to or greater than the torque of the gravity acting on the bicycle and the rider as a whole, the rear wheel will tilt forward, and the faster the braking, the more likely the bicycle will tip over.

This article focuses on the phenomenon that the hoop can automatically return after being thrown in the artistic gymnastics hoop routine, introduces the equipment parameters and performance action types of hoop routine, analyzes the translational and rotational forms of the hoop through physical ideal models such as point and rigid body, and combines the action of sliding friction to explain the three possible situations of the hoop's movement and the physical principle of its automatic return.

This article introduces the origin and development of the high jump. By explaining the mechanical principles of the high jump, the movement methods and technical characteristics of the back-over style high jump, it explains why world-class high jump athletes adopt the back-over style. The reason is that when they cross the bar, the center of gravity of the human body can pass under the bar, which has more advantages than other high jump postures

This article focuses on the question of "why cats can freely turn over in mid-air", introducing the phenomenon that cats can quickly turn over and land on all fours during a high-altitude fall, and describing the process of proposing and refuting the "tail-turning" theory, as well as the content, verification basis, and related principles of the currently accepted "curved spine" theory.

This article takes the phenomenon of children holding dumbbells and sitting on a swivel chair with accelerated arm rotation speed, and the principle of door rotation force as examples to explain the law of conservation of angular momentum (the law of conservation of momentum), and to explain the reason why figure skaters contract their bodies when spinning quickly.

This article explains the question of "why martial artists can make flying needles penetrate glass", pointing out that the speed of about 30 meters per second required for a steel needle to penetrate glass can generally be achieved by adults. The key to flying needles penetrating glass lies in the steel needle hitting the glass vertically. Sharpening the needle tip can also help it penetrate. At the same time, the examples of bullets bouncing off helmets and Li Guang shooting stones demonstrate the importance of angle. It is explained that martial artists, through long-term training, can simultaneously ensure the speed of the steel needle and control the angle of impact, thus achieving the effect of flying needles penetrating glass.

This article introduces the concept of pressure in physics through a comparative experiment between carrying a schoolbag and holding a thin string, and explains the principle that the pressure exerted on the wooden board is much greater than that exerted on the hand because the contact area between the pinhead and the wooden board is much smaller than that between the pinhead and the hand. Therefore, it's easy to push the pin into the wooden board with your hand.

This article, based on the scenario of water skiing, uses Newton's Third Law to explain why water skiers don't sink on the board. It points out that skiers rely on their skills to control the tilt angle of the board, so that the vertical component of the water's reaction force can balance their own weight, allowing them to slide quickly on the water surface.

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.