If only springs are used to absorb shocks, the oscillations of springs continue even after the vehicle has passed over a bump. The oscillations cause the wheels the jumps up and fall down till the oscillations die out. Thus, dampers or shock absorbers are used to arrest the oscillation of springs after the vehicle passes over irregular road surface.Shock absorbers are necessary used with coil springs. In case of leaf springs, the friction between leaves provides some dampening effect. However, this is not sufficient sometimes, depending upon friction between leaves. Hence, shock absorbers are necessarily used as additional damping devices.

As explained earlier, the function of the shock absorber is to dampen the vibrations of coil and leaf springs used in the suspension system. These vibrations are generated when vehicle passes over a road bump.

In modern cars, hydraulic shock absorbers are used. These absorbers use a piston and a cylinder where cylinder is filled with a suitable oil. The oil is used to dampen the oscillations of piston by a suitable arrangement. The construction of a telescopic type shock absorber has been shown in Figure

The telescopic shock absorber, mainly consists of a piston a cylinder tube and a reservoir tube. The piston has been provided with through orifices or opening so that fluid can pass from top to bottom or from bottom to top reservoir.Figure  shows the condition when absorber is compressed. This happens when vehicle passes over a bump. Under this condition the shock absorber becomes short in length. The piston rod forces the piston down into cylinder tube.Therefore, fluid under the piston is compressed to high pressure. The fluid passes forcefully through small orifices (in piston) into the moves ahead of bump or drops into a depression in the road, the shock absorber expands. Under this condition the piston moves up in the cylinder tube. Because of this, fluid is forced from upper part of cylinder tube to the lower part through the orifices provided in the piston.In both the cases, i.e. expansion and compression, fluid is forced through orifices.Because of this the motion of the piston is slowed down. This puts restriction over the spring action and vibrations of the frame are arrested in shortest time. In this way, shocks (of bump and depression of road) are absorbed by the shock absorber. It also prevents excessive oscillations of wheel when it passes over a bump and depression on the road.Shock absorbers are always provided along with springs in the suspension system of automobiles to prevent oscillations of springs.