Shock absorber

Shock absorber, any mechanism used to lessen impact in vehicles, aircraft, or stable structures. Most shock absorbers are hydraulic: They operate by forcing liquid through a small opening, an action that sets up resistance to both contraction and expansion of the spring mountings. In automobiles, shock absorbers control up-and-down vibrations and absorb impact on the car body. They are made of a piston inside an oil-filled cylinder. When the piston slides, it allows the fluid to flow through a spring-loaded valve.