Elastic scattering occurs when two or more particles collide without any loss of energy. This means that while the directions of the particles may change, the total kinetic energy of the system, or movement energy, is always conserved. The term elastic scattering is typically used in particle physics, which is the study of microscopic particles, but an elastic collision can also take place between macroscopic objects. An inelastic collision occurs when energy is lost during the collision.
The term elastic scattering comes from scattering theory, which is a set of rules and equations which describe how particles and waves interact. In the macroscopic world, when two objects collide it is usually through a physical collision. In particle physics, however, the objects may collide through other forces, including electromagnetic collisions. An elastic collision can occur between any objects and in any type of collision.
Elastic scattering is very important in particle physics. When electrons collide with other particles, for example, the collision is elastic as no energy is lost. This is known as Rutherford scattering and is a phenomenon that led to the discovery of the structure of the atom.
In the macroscopic or physical world, it is exceptionally unlikely for a true elastic collision to occur between two large objects. This is due to surrounding forces as well as the vibrations that occur inside large objects. There are some situations, however, where a collision can be approximated as elastic. This is useful as it allows for the predicted speed and direction of two objects after a collision to be estimated using simpler methods.
A common example of elastic scattering in the physical world is the collision of two billiard balls. Although a small amount of energy will be lost in this collision due to friction, this is small enough to be negligible. When two billiard balls collide, the second ball gains almost exactly the amount of energy that the first ball loses, so the total kinetic energy of the system is conserved.
Inelastic scattering occurs when the total energy of the two or more colliding objects is not conserved. In collisions between real world objects, inelastic collisions are much more common. This is mainly due to the extra vibrations which will occur when a large object collides with another, as these vibrations take up energy that would have been used for movement. Momentum, however, is always conserved in both elastic and inelastic collisions.