What Is Elastic Collision?

Alex Paul

An elastic collision occurs when the total kinetic energy, or movement energy, of two or more objects is the same after a collision as before the collision. Unlike an inelastic collision, no energy is transformed into another type. Completely elastic collisions don’t usually happen in the real world, aside from between subatomic particles, but the collision between two billiard balls is a close approximation.

Billiard balls colliding offers a good idea of elastic collision.
Billiard balls colliding offers a good idea of elastic collision.

There are two types of collisions. The first is an inelastic collision, which is more common in everyday life. During an inelastic collision, some of the kinetic energy, or movement energy, is lost on impact. This energy is converted into another type of energy, such as sound or heat. In an elastic collision, all of the kinetic energy of the two objects is retained during impact.

Before two objects collide, they each have a certain amount of kinetic energy and momentum. The amount of kinetic energy is dependent on the mass and speed of each of the objects. As a result of the fundamental law of conservation of energy, which states that energy can never be destroyed, the total energy after two objects collide must be the same as it was before the collision. If it is an elastic collision, then all of the energy remains as kinetic energy and is just moved from one object to another.

In reality, no collision between large objects is ever truly an elastic collision. This is because, when large objects hit each other, some of the kinetic energy is always lost to various other types of energy, such as sound, heat or compression of the object. In the microscopic world, such as the magnetic interaction of atoms or electrons, there is a chance that the collision is elastic, because there is no physical contact between the objects. Gravitational interactions between planets also are sometimes classed as perfectly elastic collisions.

An example of an almost elastic collision in the real world is the interaction between two billiards balls. When the white ball is struck, it gains a certain amount of kinetic energy, which it then transfers during the collision with another ball. If the collision occurs in a straight line, then all of the kinetic energy is transferred to the target ball, meaning the white ball stops dead and the target ball moves off at exactly the same speed. If the balls hit at an angle, then the kinetic energy is divided between the two.

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