A collision is said to occur between two bodies, either if they physically collide against each other or if the path of one is affected by the force exerted by the other. For a collision to take place, the actual physical contact is not necessary. In Rutherford’s scattering experiment, α-particles get scattered due to the electrostatic repulsion between the α-particle and the nucleus from a distance. The α-particle is said to have suffered collision with the nucleus.
The collisions between particles are of following types :
1. Elastic collision
If there is no loss of kinetic energy during a collision, it is called an elastic collision.
Characteristics of elastic collisions:
(i) The momentum is conserved.
(ii) Total energy is conserved.
(iii) The kinetic energy is conserved.
(iv) Forces involved during the collision are conservative.
(v) The mechanical energy is not converted into heat, light, sound, etc.
Examples:
Collision between subatomic particles, collision between glass balls, etc.
2. Inelastic collision:
If there is a loss of kinetic energy during a collision, it is called an inelastic collision.
Characteristics of inelastic collisions:
(i) The momentum is conserved.
(ii) Total energy is conserved.
(iii) The kinetic energy is not conserved.
(iv) Some or all of the forces involved are non- conservative.
(v) A part of the mechanical energy is converted into heat, light, sound, etc.
Examples:
Collision between two vehicles, collision between a ball and floor.
3. Perfectly inelastic collision:
If two bodies stick together after the collision and move as a single body with a common velocity, then the collision is said to be perfectly inelastic collision. In such collisions, momentum is conserved, but the loss of kinetic energy is maximum.
Examples:
Mud thrown on a wall and sticking to it, a man jumping into a moving trolley, a bullet fired into a wooden block and remaining embedded in it, etc.
4. Superelastic or explosive collision:
In such a collision, there is an increase in kinetic energy. This occurs if there is a release of potential energy on an impact.
Examples:
Bursting of a cracker when it hits the floor forcefully, the collision of a trolley with another may release a compressed spring and thereby releasing the energy stored in the spring.
5. Head-on or one-dimensional collision:
It is the collision in which the colliding bodies move along the same straight-line path before and after the collision.
Example:
Collision between two railway compartments.
6. Oblique or two-dimensional collision:
If two bodies do not move along the same straight-line path but lie in the s me plane before and after the collision, the collision is said to be oblique or two-dimensional collision.
Example:
Collision between two carrom coins.
Some Important Points Regarding Collisions:
- Total linear momentum is conserved at each instant of every collision.
- Total energy is conserved in all collisions.
- The total kinetic energy may or may not be conserved during a collision.
- Even for an elastic collision, the kinetic energy conservation holds after the collision is over and does not hold at every instant of the collision.
- When two bodies collide; they get deformed and may be momentarily at rest with respect to each other.
- The impact and deformation during a collision may convert part of the initial kinetic energy into heat and sound.