What is Coefficient of Restitution? Explain

Learn the significance of the coefficient of restitution in physics and mechanics. Discover its formula, examples, case studies, and statistics in this comprehensive article.


The coefficient of restitution is a fundamental concept in physics and mechanics that measures the ratio of velocities before and after a collision between two objects. It is a crucial parameter in understanding the kinetic energy transfer during collisions.


The coefficient of restitution, denoted as e, is defined as the ratio of the relative velocity of separation and the relative velocity of approach of two objects during a collision.


The formula for calculating the coefficient of restitution is: e = (v2f – v1f) / (v1i – v2i), where v1i and v2i are the initial velocities of the two objects, and v1f and v2f are their final velocities.


The coefficient of restitution helps determine whether a collision is elastic (e = 1), inelastic (0 < e < 1), or completely inelastic (e = 0). It provides valuable information on how much kinetic energy is conserved during a collision.


  • An example of a perfectly elastic collision is two billiard balls striking each other, where no kinetic energy is lost.
  • A common example of an inelastic collision is a car crash, where some kinetic energy is converted into other forms like heat and sound.

Case Studies

In sports like basketball and volleyball, understanding the coefficient of restitution helps players predict the trajectory of the ball after a bounce, enabling better coordination and gameplay.


Studies have shown that the coefficient of restitution plays a crucial role in designing efficient energy-absorbing materials for car bumpers and sports equipment to minimize injuries during collisions.

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