What is collision???

Please do not give any link!!!

The collision between 2 objects is defined as that interactions due to which the momentum kinetic energy of both the objects changes.

it is not necessary in the process of collision that the objects makes the contact with each other

for ex : in the collision of a bus and a car both of them makes contact with each other but in the collision of light particles , like electron, proton the particles does not touches to each other.

there are two types of collision

1) elastic

2) in- elastic