Spring, can you imagine? Press down and loosen your hand, and the spring will come back after a moment's swoop. This is called free rebound. The shock absorber has a cylinder with a piston inside. When the shock is compressed and springs out, the piston will move in the cylinder. Because the piston moves toward which end, it compresses the space at which end. In this way, the oil pressure at that end rises, and the piston has several small holes. The oil will flow from the small hole through the piston to the end where the space becomes larger. Because the hole is small, there is resistance when the oil flows through. This will make the damping no matter whether it is pressed down or extended. And slower, it has a very soft shock absorption effect, it will not be the appearance of the bounced down.