COLLISION ,TYPES OF COLLISIONS
Collision
Collision is an isolated event in which a strong force acts between two or more bodies for a short time as a result of which the energy and momentum of the interacting particle change.
In collision particles may or may not come in real touch e.g. in collision between two billiard balls or a ball and bat, there is physical contact while in collision of alpha particle by a nucleus (i.e. Rutherford scattering experiment) there is no physical contact.
(1) Stages of collision : There are three distinct identifiable stages in collision, namely, before, during and after. In the before and after stage the interaction forces are zero. Between these two stages, the interaction forces are very large and often the dominating forces governing the motion of bodies. The magnitude of the interacting force is often unknown, therefore, Newton’s second law cannot be used, the law of conservation of momentum is useful in relating the initial and final velocities.
(2) Momentum and energy conservation in collision
(i) Momentum conservation : In a collision, the effect of external forces such as gravity or friction are not taken into account as due to small duration of collision (Dt) average impulsive force responsible for collision is much larger than external force acting on the system and since this impulsive force is 'Internal' therefore the total momentum of system always remains conserved.
(ii) Energy conservation : In a collision 'total energy' is also always conserved. Here total energy includes all forms of energy such as mechanical energy, internal energy, excitation energy, radiant energy or even mass energy.
These laws are the fundamental laws of physics and applicable for any type of collision but this is not true for conservation of kinetic energy.
(3) Types of collision : (i) On the basis of conservation of kinetic energy.
(ii) On the basis of the direction of colliding bodies