Collision

In physics, a collision is any event in which two or more bodies exert forces on each other in a relatively short time.

Comparing this with the latter equation gives va2•vb2 = 0, so they are perpendicular unless va2 is the zero vector (which occurs if and only if the collision is head-on).

In a perfect inelastic collision, i.e., a zero coefficient of restitution, the colliding particles coalesce.

Collisions of an animal's foot or paw with the underlying substrate are generally termed ground reaction forces.

An important research topic in prosthetics is quantifying the forces generated during the foot-ground collisions associated with both disabled and non-disabled gait.

In particular, hypervelocity is velocity so high that the strength of materials upon impact is very small compared to inertial stresses.

An impact under extreme hypervelocity results in vaporization of the impactor and target.

A 3D simulation demonstrating collision with a ball knocking over some blocks.
A 3D simulation demonstrating a collision with a ball knocking over a bunch of blocks
Deflection happens when an object hits a plane surface. If the kinetic energy after impact is the same as before impact, it is an elastic collision. If kinetic energy is lost, it is an inelastic collision. The diagram does not show whether the illustrated collision was elastic or inelastic, because no velocities are provided. The most one can say is that the collision was not perfectly inelastic, because in that case the ball would have stuck to the wall.
Video of the hypervelocity impact of NASA’s Deep Impact probe on comet Tempel 1 .