elastic that they can be approximated as such. In this case, the coefficient of restitution equals one. An inelastic collision is one in which part of the kinetic energy is changed to some other form of energy in the collision. Momentum is conserved in inelastic collisions (as it is for elastic collisions), but one cannot track the kinetic energy through the collision since some of it is converted to other forms of energy. In this case, coefficient of restitution is not equal to one. In any type of collision there is a phase when for a moment colliding bodies have the same velocity along the line of impact. Then the kinetic energy of bodies reduces to its minimum during this phase and may be called a maximum deformation phase for which momentarily the coefficient of restitution becomes one. Collisions in ideal gases approach perfectly elastic collisions, as do scattering interactions of sub-atomic particles which are deflected by the electromagnetic force. Some large-scale interactions like the slingshot type gravitational interactions between satellites and planets are almost perfectly elastic. Collisions between hard spheres may be nearly elastic, so it is useful to calculate the limiting case of an elastic collision. The assumption of conservation of momentum as well as the conservation of kinetic energy makes possible the calculation of the final velocities in two-body collisions. Allision In maritime law, it is occasionally desirable to distinguish between the situation of a vessel striking a moving object, and that of it striking a stationary object. The word "allision" is then used to mean the striking of a stationary object, while "collision" is used to mean the striking of a moving object. Thus, when two vessels run against each other, courts typically use the term collision whereas when one vessel runs against another, they typically use the term allision. The fixed object could also be a bridge or dock. While there is no great difference between the two terms and often they are even used interchangeably, determining the difference helps clarify the circumstances of emergencies and adapt accordingly. In the case of Vane Line Bunkering, Inc. v. Natalie D M/V, it was established that there was the presumption that the moving vessel is at fault, stating that "presumption derives from the common-sense observation that moving vessels do not usually collide with stationary objects unless the [moving] vessel is mishandled in some way". This is also