The event or the process, in which two bodies either coming in contact with each other or due to mutual interaction at distance apart, affect each other motion (velocity, momentum, energy or direction of motion) is defined as a collision.
`text(Changes during collision/Impact :)`
(a) During impact each of the colliding bodies experiences a strong force, hence during impact each of the bodies changes its momentum, but as a whole, the total momentum of the system does not change.
(b) Impact is practically followed by emission of light, sound, heat etc. Therefore, during an impact or collision, the mechanical energy of the system does not remain constant whereas the total energy of the system remains unchanged.
(c) In ideal case of collision such as collision between gas molecules, atoms, electrons etc., the K.E. of the system of colliding particles remains constant before and after the impact. This type of collision is known as perfectly elastic collision. Remember that, during collision, the K.E. of the particles changes due to large impulsive force.
(d) In some collisions, the K.E. of the system changes. This type of collision cannot be called as perfectly elastic.
(e) For perfectly elastic collision, the K.E. of the system at the beginning and at the end of the impact must remain constant, but not during the impact.
(f) If the colliding particles/bodies stick together, they move together with same velocity. This type of collision is known as perfectly inelastic collision. In this process some times K.E. is lost completely. For example, in dropping a stone into mud, the stone loses its total K.E. Some times, K.E. is fractionally lost, for example, the collision of a bullet with a hanging target.
(g) Relative velocity of the bodies just after the collision ( velocity of separation) may or may not be equal to that before the collision along the line of impact (velocity of approach)
`text(Insight into collision :)`
Consider two balls moving as shown in the fig(1.a). If `v_1 > v_2`, both the balls will eventually collide. Just at the instant of collision the point of contact A has a larger velocity ( `v_1`) compared to the contact point B . Let us assume that the two bodies interact (remain in contact) for a small time `Deltat` , for this period points A and B must move through equal distance. This is possible only if the contact point gets deformed. The deformation is maximum when the two balls have equal velocities. A fraction of total kinetic energy gets converted into elastic potential energy. If the balls are made of elastic material, they regain their original shape and gets separated with changed velocities. During the entire process both the ball keep on pushing each other, as a result of which, the velocity of first ball decreases from `v_1` and that of second ball increases from `v_2`. If the balls regain their original shape, the entire elastic potential energy is converted back to kinetic energy. Remember that we are neglecting energy loss on account of heat developed, noise produced etc. If the material of the bodies are perfectly inelastic, they continue to move with the deformed shape. In this case both the bodies have a common velocity (when their deformation is maximum) and they move together. Collision is said to be perfectly inelastic in this case. For partially inelastic material, the deformed body tries to regain its shape but is capable of achieving it partially. Some kinetic energy is still lost and remains in form of elastic potential energy.
The event or the process, in which two bodies either coming in contact with each other or due to mutual interaction at distance apart, affect each other motion (velocity, momentum, energy or direction of motion) is defined as a collision.
`text(Changes during collision/Impact :)`
(a) During impact each of the colliding bodies experiences a strong force, hence during impact each of the bodies changes its momentum, but as a whole, the total momentum of the system does not change.
(b) Impact is practically followed by emission of light, sound, heat etc. Therefore, during an impact or collision, the mechanical energy of the system does not remain constant whereas the total energy of the system remains unchanged.
(c) In ideal case of collision such as collision between gas molecules, atoms, electrons etc., the K.E. of the system of colliding particles remains constant before and after the impact. This type of collision is known as perfectly elastic collision. Remember that, during collision, the K.E. of the particles changes due to large impulsive force.
(d) In some collisions, the K.E. of the system changes. This type of collision cannot be called as perfectly elastic.
(e) For perfectly elastic collision, the K.E. of the system at the beginning and at the end of the impact must remain constant, but not during the impact.
(f) If the colliding particles/bodies stick together, they move together with same velocity. This type of collision is known as perfectly inelastic collision. In this process some times K.E. is lost completely. For example, in dropping a stone into mud, the stone loses its total K.E. Some times, K.E. is fractionally lost, for example, the collision of a bullet with a hanging target.
(g) Relative velocity of the bodies just after the collision ( velocity of separation) may or may not be equal to that before the collision along the line of impact (velocity of approach)
`text(Insight into collision :)`
Consider two balls moving as shown in the fig(1.a). If `v_1 > v_2`, both the balls will eventually collide. Just at the instant of collision the point of contact A has a larger velocity ( `v_1`) compared to the contact point B . Let us assume that the two bodies interact (remain in contact) for a small time `Deltat` , for this period points A and B must move through equal distance. This is possible only if the contact point gets deformed. The deformation is maximum when the two balls have equal velocities. A fraction of total kinetic energy gets converted into elastic potential energy. If the balls are made of elastic material, they regain their original shape and gets separated with changed velocities. During the entire process both the ball keep on pushing each other, as a result of which, the velocity of first ball decreases from `v_1` and that of second ball increases from `v_2`. If the balls regain their original shape, the entire elastic potential energy is converted back to kinetic energy. Remember that we are neglecting energy loss on account of heat developed, noise produced etc. If the material of the bodies are perfectly inelastic, they continue to move with the deformed shape. In this case both the bodies have a common velocity (when their deformation is maximum) and they move together. Collision is said to be perfectly inelastic in this case. For partially inelastic material, the deformed body tries to regain its shape but is capable of achieving it partially. Some kinetic energy is still lost and remains in form of elastic potential energy.
