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Recoil Energy Calculator.

Calculate nonrelativistic recoil kinetic energy from momentum and mass.

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Set your values

Results update as you type.

Energy: 4 J

Energy

4.000000J

Results update automatically as you type.

Use Cases

Firearm Recoil Estimation

Estimate the kinetic energy of a firearm's recoil using the momentum of the ejecta and the mass of the gun.

Example: A rifle with a mass of 4 kg and ejecta momentum of 8 kg·m/s gives recoil energy of 8 J.

Physics Problem Solving

Quickly compute kinetic energy from momentum and mass for homework or lab exercises in classical mechanics.

Example: Given p = 10 kg·m/s and m = 2 kg, KE = 25 J.

Frequently Asked Questions

How is recoil energy calculated?
The calculator uses the nonrelativistic formula KE = p² / (2m), where p is momentum in kg·m/s and m is the recoiling mass in kg. It assumes speeds much less than the speed of light.
What units are used for the inputs and output?
Momentum is entered in kg·m/s, mass in kg, and the resulting recoil kinetic energy is given in joules (J).
Can I use this for relativistic speeds?
No, this calculator is specifically for nonrelativistic cases. For speeds approaching the speed of light, relativistic formulas are required.

Tips & Common Mistakes

Tips

  • Ensure momentum and mass are in the correct units (kg·m/s and kg) before calculating.
  • For accurate results, use the mass of the entire recoiling object, not just a part.
  • Remember that this calculator is for nonrelativistic speeds; for high-speed particles, use relativistic formulas.
  • Double-check your momentum value: it is the product of mass and velocity of the ejecta.

Common Mistakes to Avoid

  • Using mass in grams instead of kilograms without converting.
  • Confusing momentum with kinetic energy; they are different quantities.
  • Applying this nonrelativistic formula to objects moving at relativistic speeds.

Last updated: August 13, 2026