Bicycles are common means of transportation in our daily life, such as ordinary heavy bicycles, light bicycles, mountain bikes, baby carriages, racing cars and electric bicycles. It is simple in structure, convenient and practical. Common bicycles involve a lot of physical knowledge, including mechanical, thermal and optical knowledge such as lever, axle, friction, pressure and energy conversion. Here is a comprehensive introduction to the knowledge about bicycles. 1. Mechanical knowledge 1. Friction (1) bicycle tires, handlebars, pedals and brake pads are engraved with some patterns. Increase the roughness of the contact surface and increase the friction. (2) Always apply some lubricating oil on the axle to reduce the roughness of the contact surface and reduce the friction. (3) Each shaft is equipped with balls, which changes sliding friction into rolling friction, reduces friction and facilitates rotation. (4) When braking, it is necessary to tighten the brake handle to increase the pressure between the brake pad and the rim, thus increasing the friction. (5) Push the bicycle tightly. When a bicycle moves forward by inertia, the friction between the front and rear wheels is backward, and these two forces are the resistance of the bicycle. 2. Pressure (1) In general, the landing area of adequately inflated bicycle tires is about S = 2×10 cm× 5 cm =100× cm2. When an ordinary adult rides a bicycle forward, the pressure of the bicycle on the ground is about F=(500N+ 150N)=650N, and it can be calculated that the pressure of the bicycle on the ground is 6.5× 104 Pa. (2) A washer should be added at the nut of the shaft to increase the stress area and reduce the pressure. (3) The pedal of the bicycle should be flattened to increase the pressure. (4) The inner tube of the bicycle should be full of air. When the volume and temperature of the gas are constant, the greater the mass of the gas, the greater the pressure. (5) Make the bicycle seat flat to increase the stress area, thus reducing its pressure on the body. 3. Axle (1) The handlebar of a bicycle is equivalent to the axle, the handlebar is equivalent to the wheel, and the front axle is the axle. As shown in figure 3. (2) The pedal and the central axle of a bicycle are also equivalent to an axle, which is essentially a labor-saving lever. (3) The flywheel of a bicycle is also equivalent to a labor-saving axle. (4) In terms of lever, the brake handle of bicycle is equivalent to a labor-saving lever. (5) Inertia (1) When a person rides a bicycle forward, the bicycle still moves forward after stopping pedaling. Because it has inertia. (2) When a person rides a bicycle forward, if there is an emergency, under normal circumstances, the brakes should be tightened first, then the front brakes, or tightened together before and after to prevent people from flying forward due to inertia. 6. Energy conversion (1) When a person rides a bicycle downhill, the speed is getting faster and faster. It is because the gravitational potential energy of people and bicycles is converted into kinetic energy of people and bicycles when going downhill. (2) When riding a bicycle uphill, people should pedal several times more to increase the speed and kinetic energy of people and bicycles, so that the kinetic energy can be converted into gravitational potential energy when climbing uphill, so as to climb higher. (3) There is a spring hanging on the bicycle ladder. When the spring bounces, its elastic potential energy is converted into kinetic energy. The ladder will spring up automatically. 7. Acoustics (1) The sound of bicycle metal stirrups is caused by the constant vibration of the bell cover, while the sound of the whistle is caused by the constant vibration of the gas in the whistle. 8. In gear transmission (1), as shown in Figure 5, if the gear edge line speed is V and the gear radius is R, then V = Ω R. Second, the knowledge that bicycle tires can't be filled with too much heat in summer, in order to prevent bicycle tires from bursting, because for a certain mass and volume of gas, the higher the temperature, the greater the pressure. When the pressure reaches a certain level, if it exceeds the tire, Third, the knowledge of optics. In daily life, a reflector is installed at the back of the bicycle, and its design is very clever. As shown in fig. 6, it is a three-dimensional right angle composed of three plane mirrors perpendicular to each other, and its inner surface is called a corner reflector. When the light is aimed at the taillight from any angle, it can be "reversely reflected". When the light is aimed at the reflector, it will be easy for people behind to see. At night, when the car light shines on the front bicycle taillight, the reflected light can be reflected to the car regardless of the incident direction. Its light intensity is far greater than the general diffuse light, just like a red light, enough for car drivers to observe. Fourthly, in terms of electricity, some bicycles are equipped with small power generation devices, which use friction to rotate, just like the hand-cranked generators we see in the laboratory. The generated electric energy is used to supply lights to work and play a certain lighting role.