Impacts can be classified in various forms, primarily under two subgroups: central impact and oblique impact. A central impact occurs when two objects collide head-on, possessing opposite velocities aligned along the line of impact. Conversely, an oblique impact occurs when two objects collide at an angle, resulting in a modification of both direction and velocity.

The coefficient of restitution is a metric for understanding the dynamics of impacts. It quantifies the ratio of relative velocity after the impact to that before the impact, reflecting the elasticity of the collision. This coefficient ranges from zero to one, with a value of one indicating a perfectly elastic impact where no kinetic energy is lost. However, achieving absolute elasticity is unattainable, as some kinetic energy is inevitably dissipated during the collision.

Several factors influence the coefficient of restitution, including impact velocity, as well as the size and shape of the colliding bodies. When the coefficient is zero, the impact is termed a plastic impact, where colliding particles adhere together and move with a shared velocity post-collision. The coefficient of restitution essentially determines the bounce-back behavior of an object, with higher values indicating a more pronounced rebound to the original speed. In practical terms, a perfectly elastic impact remains an idealized scenario, while the coefficient of restitution serves as a pivotal parameter in gauging the impact's bounciness.