How does a shock absorber reduce bouncing?

A vehicle’s suspension lets its wheels move up and down relative to the body. A spring supports the body and changes shape as the wheel moves over a bump. Compressing the spring stores energy. As the spring expands again, it can return that energy to moving parts, producing repeated bouncing.

A conventional shock absorber is a damper: a device that resists movement and reduces this repeated motion. Its piston moves through oil inside a cylinder. Oil must pass through small valve passages as the piston moves. Resistance to that flow produces a force opposing the relative movement between the damper’s ends.

The spring and damper therefore do different jobs. The spring stores and returns energy; the damper transfers some mechanical energy into thermal energy in the oil and surrounding parts. Heat then spreads to the surroundings. Damping acts during both compression and extension, although real valves often provide different resistance in the two directions.

The spring responds to how far it is compressed, while an ideal damper responds to how quickly its ends move relative to each other. At rest, the damper’s force is zero even though the compressed spring still pushes. Faster relative movement produces a larger opposing force in a simple damper model. Actual suspension movement also depends on the body, wheels, road and other forces.