Collisions can be categorized into two main types: elastic and inelastic. In an elastic collision, both momentum and kinetic energy are conserved. This means that after the collision, the total energy and momentum of the objects involved remain the same as before the collision. A common example is the collision of two billiard balls. In contrast, an inelastic collision occurs when momentum is conserved, but kinetic energy is not. This type of collision often results in some energy being transformed into other forms, such as heat or sound. A typical example is a car crash, where the vehicles crumple and stick together, losing kinetic energy in the process.