This question already has an answer here:
First of all, I tell you that I know there is same question available which is already answered, but no answer cleared my doubt, that's why I am asking the question in more detail.
Let there be a collision between two bodies with velocity in same direction before and after the collision. During the collision of two bodies, heat energy is produced, so particles of the bodies start vibrating rapidly about there positions, due to transfer of kinetic energy of the bodies to constituent particles. This must lead to reduce in velocity of the two bodies, and consequently reduce in total momentum.
Thus, I am saying there may be loss of kinetic energy, but there should be loss of momentum too.
Please tell me where I am wrong.
Also please, don't state the law of conservation of momentum or its modified form and try to explain in practical terms.