In the realm of physics, the study of collisions plays a crucial role in understanding how objects interact. Collisions can be either elastic or inelastic, each with unique characteristics. The key question in the study of inelastic collisions is whether momentum is conserved, despite the apparent loss of kinetic energy.

Woman shrugging
✅ AI Essay Writer ✅ AI Detector ✅ Plagchecker ✅ Paraphraser
✅ Summarizer ✅ Citation Generator

Understanding Inelastic Collisions

In an inelastic collision, unlike an elastic collision, the colliding objects do not retain their kinetic energy. Instead, some of the kinetic energy is transformed into other forms, such as heat or sound, often referred to as internal kinetic energy. A perfectly inelastic collision is an extreme case where the colliding objects stick together post-collision.

Momentum in Collisions

Momentum, defined as the product of an object’s mass and velocity, is a fundamental concept in collisions. According to the law of conservation of momentum, the total momentum of a closed system remains constant if no external forces act upon it. This principle applies to all types of collisions, including inelastic collisions.

In inelastic collisions, even though kinetic energy is not conserved, momentum is conserved. This is because momentum depends solely on the mass and velocity of the objects, and not on how the kinetic energy is distributed or transformed during the collision.

Case Study: Hockey Puck and Goalie

Consider a scenario in ice hockey where a puck collides with a goalie. When the puck, having a certain velocity and kinetic energy, hits the goalie and stops, it appears as though kinetic energy is lost. However, the momentum before and after the collision, when considering both the puck and the goalie, remains the same.

Analyzing the Collision

  1. Before Collision: The puck has a certain momentum, and the goalie is stationary.
  2. After Collision: The system’s total momentum, which includes both the puck and the goalie, is the same as before the collision.

The Role of External Forces

External forces, such as friction, can affect the momentum of the objects involved in the collision. However, in the idealized scenarios often considered in physics, where external forces are negligible, momentum conservation holds true even in inelastic collisions.

Elastic vs. Inelastic Collisions

While momentum is conserved in both elastic and inelastic collisions, the conservation of kinetic energy differentiates them. In elastic collisions, kinetic energy is conserved, while in inelastic collisions, some kinetic energy is converted into other forms of energy.


In conclusion, momentum is indeed conserved in inelastic collisions, regardless of the transformation or loss of kinetic energy. This conservation law remains a cornerstone in understanding the dynamics of collisions, from the simple interactions of hockey pucks and goalies to more complex systems in physics. Understanding the nuances of momentum and energy conservation helps in comprehending the broader principles governing motion and interactions in our physical world.


Is kinetic energy conserved in an inelastic collision?

No, kinetic energy is not conserved in an inelastic collision. In such collisions, a portion of the kinetic energy is transformed into other forms of energy, such as heat, sound, or internal kinetic energy. This transformation results in a decrease in the system’s kinetic energy post-collision, unlike in elastic collisions where kinetic energy is conserved.

What are some real-life examples of inelastic collisions?

Real-life examples of inelastic collisions include:

  1. Vehicle Accidents: When cars collide and crumple upon impact, kinetic energy is converted into other forms of energy, primarily in deforming the vehicles.
  2. Sports Collisions: For instance, a football player tackling another, where both players slow down and energy is dissipated in the form of sound and deformation.
  3. Play-Doh or Clay Impact: When a lump of Play-Doh or clay is thrown against a wall and deforms upon impact, losing its kinetic energy in the process.

How do you calculate the momentum before and after an inelastic collision?

To calculate the momentum before and after an inelastic collision, you consider the mass and velocity of each object involved in the collision. Before the collision, you assess the momentum of each object separately. After the collision, especially in a perfectly inelastic scenario where objects stick together, you consider the combined mass and the new velocity of the merged object or system. The key principle here is that the total momentum of the system before the collision is equal to the total momentum after the collision, following the law of conservation of momentum. This calculation does not require a detailed breakdown of the kinetic energy changes, which is where the inelastic nature of the collision primarily manifests.


Opt out or Contact us anytime. See our Privacy Notice

Follow us on Reddit for more insights and updates.

Comments (0)

Welcome to A*Help comments!

We’re all about debate and discussion at A*Help.

We value the diverse opinions of users, so you may find points of view that you don’t agree with. And that’s cool. However, there are certain things we’re not OK with: attempts to manipulate our data in any way, for example, or the posting of discriminative, offensive, hateful, or disparaging material.

Your email address will not be published. Required fields are marked *


Register | Lost your password?