Elastic Collision Calculator

Enter the masses and initial velocities of two objects to calculate final velocities, kinetic energy conservation, and momentum after a perfectly elastic collision.

Created by Luis GonzalezLast updated: May 9, 2026

How to Use This Calculator

1
Enter the mass of object 1 (m₁)
Input the mass of the first object in kilograms. This must be a positive value.
2
Enter the initial velocity of object 1 (v₁)
Input the velocity of object 1 before the collision. Use negative values for motion to the left.
3
Enter the mass of object 2 (m₂)
Input the mass of the second object in kilograms. This must be a positive value.
4
Enter the initial velocity of object 2 (v₂)
Input the velocity of object 2 before the collision. Use negative values for motion to the left, or 0 if stationary.
5
Review the post-collision velocities and energy metrics
Examine the final velocities of both objects, initial and final kinetic energies, momentum, and the coefficient of restitution.

Example Calculation

A 2 kg object moving right at 5 m/s collides elastically with a stationary 3 kg object.

Mass 1 (m₁)

Initial Velocity of Object 1 (v₁)

Mass 2 (m₂)

Initial Velocity of Object 2 (v₂)

Results

-1.0000 m/s

Tips

Direction Matters

Always use positive values for motion to the right and negative values for motion to the left. Incorrect signs will lead to incorrect final velocities and momentum calculations.

Conservation Laws

In a perfectly elastic collision, both momentum and kinetic energy are conserved. The calculator's output for initial and final kinetic energy and momentum should reflect this equality.

Coefficient of Restitution (e)

For perfectly elastic collisions, the coefficient of restitution (e) is always 1. If 'e' is less than 1, the collision is inelastic, meaning some kinetic energy was lost.

Analyzing Impacts with the Elastic Collision Calculator

The Elastic Collision Calculator provides a detailed analysis of one-dimensional, perfectly elastic collisions, computing post-collision velocities, kinetic energy, momentum, and the coefficient of restitution. This tool is fundamental to physics, where elastic collisions serve as an idealized model for understanding interactions between objects, such as billiard balls or gas molecules. In such collisions, both momentum and kinetic energy are conserved, a principle that underpins many areas of engineering and sports science.

Real-World Manifestations of Elastic Collisions

While perfectly elastic collisions are an idealized model in physics, they are closely approximated in various real-world scenarios, offering valuable insights into the conservation of momentum and kinetic energy. Examples include the collision of billiard balls on a pool table, where minimal energy is lost to heat or sound, or the interactions of gas molecules at high temperatures within a container. The principles derived from elastic collisions are applied in engineering for designing impact absorption systems, such as crumple zones in cars (though these are largely inelastic, the elastic model informs initial impact forces), and in sports science to analyze equipment performance, like the coefficient of restitution for golf balls (which is typically around 0.8-0.9, not a perfect 1). These conservation laws are essential for predicting outcomes in a wide range of physical interactions.

Analyzing Inelastic and Partially Elastic Collisions

While this calculator focuses on perfectly elastic collisions (where the coefficient of restitution, e=1), real-world impacts are often inelastic (e<1) or even perfectly inelastic (e=0). In inelastic collisions, some kinetic energy is lost, typically converted into heat, sound, or deformation of the colliding objects. The formulas for final velocities are modified to incorporate this energy loss. For instance, in a perfectly inelastic collision, objects stick together after impact, and their final velocities are identical. The coefficient of restitution quantifies this energy loss, with values ranging from 0 (perfectly inelastic) to 1 (perfectly elastic). Understanding these variants is crucial for modeling impacts in engineering (e.g., car crashes, where energy absorption is designed for safety), sports equipment design (e.g., how a tennis ball deforms upon impact), and even in astrophysics for planetary collisions.

💡 For analyzing other momentum-based scenarios, our Free Recoil Velocity Calculator can determine the kickback velocity of a firearm or other propelled object.

Calculating a Collision Between Two Objects

Consider a 2 kg object (m₁) moving to the right at 5 m/s (v₁) that collides elastically with a stationary 3 kg object (m₂).

Input Mass 1 (m₁): 2 kg
Input Initial Velocity of Object 1 (v₁): 5 m/s
Input Mass 2 (m₂): 3 kg
Input Initial Velocity of Object 2 (v₂): 0 m/s

The calculator applies the conservation laws of momentum and kinetic energy to find the final velocities:

Final Velocity of Object 1 (v₁f): v1f = ((m1 - m2) / (m1 + m2)) * v1 + ((2 * m2) / (m1 + m2)) * v2 v1f = ((2 - 3) / (2 + 3)) * 5 + ((2 * 3) / (2 + 3)) * 0 v1f = (-1 / 5) * 5 + (6 / 5) * 0 = -1 + 0 = -1 m/s
Final Velocity of Object 2 (v₂f): v2f = ((2 * m1) / (m1 + m2)) * v1 + ((m2 - m1) / (m1 + m2)) * v2 v2f = ((2 * 2) / (2 + 3)) * 5 + ((3 - 2) / (2 + 3)) * 0 v2f = (4 / 5) * 5 + (1 / 5) * 0 = 4 + 0 = 4 m/s

The results are:

Final Velocity of Object 1: -1.0000 m/s (moving left)
Final Velocity of Object 2: 4.0000 m/s (moving right)
Initial Kinetic Energy: 25.0000 J
Final Kinetic Energy: 25.0000 J (conserved)
Momentum: 10.0000 kg·m/s (conserved)
Coefficient of Restitution: 1.0000 (perfectly elastic)

This scenario shows that after the collision, the 2 kg object reverses direction, while the 3 kg object moves forward, with both kinetic energy and momentum perfectly conserved.

💡 To understand how objects behave under gravity before a collision, our Free Fall Distance Calculator can help you determine the distance an object falls over time.

Idealized Models and Conservation Laws in Physics

The concept of a perfectly elastic collision serves as an ideal model in physics, foundational to understanding the unwavering conservation of both momentum and kinetic energy within a closed system. These conservation laws are not merely theoretical constructs but are fundamental principles taught in physics curricula worldwide, from high school AP Physics standards to university-level mechanics. While real-world collisions are often inelastic, the elastic model provides a crucial baseline for analysis and engineering design. For instance, in crash safety systems, engineers use the principles of momentum transfer to design vehicles that absorb impact energy, even if the collision itself is highly inelastic. The elastic model allows physicists to isolate and study the fundamental interactions without the complexities of energy dissipation, enabling a deeper understanding of particle interactions and material properties.

Frequently Asked Questions

What is an elastic collision?

An elastic collision is an idealized type of collision in physics where the total kinetic energy of the system is conserved before and after the collision, in addition to the conservation of momentum. In such collisions, objects bounce off each other without any loss of energy due to deformation, heat, or sound, making it a foundational model for analyzing interactions between particles or billiard balls.

What are the key characteristics of an elastic collision?

The key characteristics of an elastic collision are the conservation of both total momentum and total kinetic energy. This means the sum of the masses times their velocities remains constant, and the sum of 0.5 times mass times velocity squared also remains constant. Additionally, the relative velocity of approach between the objects before the collision equals the negative of their relative velocity of separation after the collision.

How does an elastic collision differ from an inelastic collision?

The fundamental difference between an elastic and an inelastic collision lies in the conservation of kinetic energy. In an elastic collision, kinetic energy is conserved. In contrast, in an inelastic collision, some kinetic energy is lost, typically converted into other forms of energy such as heat, sound, or deformation of the objects. Momentum is conserved in both types of collisions, provided no external forces act on the system.