Final answer:
When two objects hit each other, a collision occurs. There are inelastic collisions, where the objects stick together and form a single composite object, and elastic collisions, where the objects bounce off each other and move away at the same relative speed.
Step-by-step explanation:
When two objects hit each other, a collision occurs. There are different types of collisions depending on what happens to the objects after the collision.
If the objects stick together and form a single composite object, it is called an inelastic collision. In an inelastic collision, the total mass of the composite object is the sum of the masses of the original objects, and the new object moves with a velocity determined by the conservation of momentum.
On the other hand, if the objects bounce off each other and move away at the same relative speed at which they approached each other, it is called an elastic collision. In an elastic collision, the total kinetic energy of the system is conserved.