What is the principle of bicycle shock absorber?

When the frame (or car body) vibrates with the axle, the piston in the shock absorber moves up and down, and the oil in the shock absorber cavity repeatedly flows from one cavity to another through different small holes. At this time, the friction between the hole wall and the engine oil and the internal friction between the engine oil molecules form a damping force on the vibration, so that the vibration energy of the automobile is converted into engine oil heat energy, which is absorbed by the shock absorber and radiated to the atmosphere. When the oil channel section and other factors are constant, the damping force increases or decreases with the relative movement speed of the frame and axle (or wheel), and it is related to the viscosity of oil.