Final answer:
A frictionless collision that is completely elastic is called a perfectly elastic collision, where both kinetic energy and momentum are conserved. In contrast, inelastic collisions, including perfectly inelastic collisions, involve kinetic energy not being fully conserved.
Step-by-step explanation:
In a frictionless collision where the collision is completely elastic, the type of collision occurring is a perfectly elastic collision. This type of collision is characterized by the conservation of both kinetic energy and momentum; there are no losses in kinetic energy due to the collision, which is the criteria for an event to be classified as elastic.
An inelastic collision, on the other hand, is one where kinetic energy is not conserved. A perfectly inelastic collision is the most extreme case, where the colliding objects stick together after the impact. In both inelastic and perfectly inelastic collisions, some of the kinetic energy is transformed into other forms of energy, such as heat or sound.
Interestingly, while perfectly elastic collisions are rare in macroscopic settings due to various forms of energy dissipation, such collisions can occur at a subatomic level where two particles can collide without losing any kinetic energy.