Shocks provide resistance by forcing hydraulic fluid (oil) through valves in the piston as it moves up and down. Because the oil cannot be compressed, only a certain amount of fluid can be forced through these valves, which creates resistance to vehicle movement.
Struts integrate numerous suspension parts into one compact assembly, including the coil spring, spring seats, shock absorber, strut bearing, and steering knuckle. Its spring can support the weight of the vehicle, while moving to adapt to road irregularities. The internal shock absorber dampens movement of the spring as it compresses and rebounds during vehicle travel. The strut housing serves as a structural part of the suspension system and connects the upper strut bearing to the lower ball joint so that the entire assembly can pivot when the steering wheel is turned.