There are two kinds of collision; elastic collision and inelastic collision. In an elastic collision, both momentum and kinetic energy are conserved.
However, in an inelastic collision, kinetic energy is not conserved. So, when the bumper of two cars collide, the cars come to a stop because the collision is inelastic.
No you can't cuz,if you put water instead of clock oil in Millikan oil drop your experiment will fail and it won't turn out the way you wanted it to be
