Physics

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Reduced Mass Calculator.

Calculate two-body reduced mass.

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Reduced mass: 0.666667 kg

Reduced mass

0.666667kg

Results update automatically as you type.

Use Cases

Orbital mechanics calculations

Use reduced mass to analyze the relative motion of two celestial bodies, such as a planet and a star, simplifying the two-body problem into an equivalent one-body problem.

Example: Calculate the reduced mass of Earth (5.972×10^24 kg) and the Moon (7.342×10^22 kg).

Molecular vibration analysis

In chemistry and physics, reduced mass is used to determine the vibrational frequency of diatomic molecules, which depends on the masses of the two atoms.

Example: Find the reduced mass of a hydrogen chloride (HCl) molecule using masses of hydrogen and chlorine.

Frequently Asked Questions

What is reduced mass?
Reduced mass is an effective inertial mass used in two-body problems. It is calculated as the product of the two masses divided by their sum. It simplifies the motion of two interacting bodies into a single-body problem.
How do I use this calculator?
Enter the mass of the first object (Mass 1) and the mass of the second object (Mass 2) in kilograms. The calculator will compute the reduced mass using the formula μ = (m1*m2)/(m1+m2).
What are the units of reduced mass?
The reduced mass is expressed in kilograms (kg), the same unit as the input masses. This is because the formula divides the product of two masses (kg²) by the sum (kg), resulting in kg.

Tips & Common Mistakes

Tips

  • Ensure both masses are entered in kilograms (kg) for consistent results.
  • If you have masses in other units, convert them to kilograms first (1 g = 0.001 kg, 1 tonne = 1000 kg).
  • The reduced mass is always less than the smaller of the two masses, so use that as a sanity check.
  • For equal masses, the reduced mass is half of one mass.

Common Mistakes to Avoid

  • Forgetting to convert masses to kilograms before entering them, leading to incorrect reduced mass values.
  • Using the formula incorrectly, such as adding masses instead of multiplying them in the numerator.
  • Confusing reduced mass with center-of-mass mass; reduced mass is for relative motion, not total mass.

Last updated: August 13, 2026