Gravity Calculator
Use these tools to calculate weight under different gravity and gravitational force between two masses.
1) Weight from Mass
Formula: W = m × g
2) Force Between Two Masses
Formula: F = G × m₁ × m₂ / r²
What Is Gravity?
Gravity is the attractive force between masses. It keeps planets in orbit, pulls objects toward the ground, and gives your body its weight. In daily life, we notice gravity as the force that makes things fall. In physics, gravity is one of the fundamental interactions in nature.
Two Useful Gravity Calculations
Weight on a Planet or Moon
Weight is not the same as mass. Your mass stays constant, but your weight changes with local gravitational acceleration. On Earth, gravity is about 9.81 m/s², while on the Moon it is only about 1.62 m/s². That is why astronauts appear lighter on the Moon.
- Mass: amount of matter (kg)
- Weight: force due to gravity (newtons, N)
- Equation: W = m × g
Gravitational Force Between Two Objects
Newton's law of universal gravitation describes the attraction between any two masses. The force increases when masses increase and decreases quickly as distance grows.
- Equation: F = G × m₁ × m₂ / r²
- G: gravitational constant = 6.67430 × 10⁻¹¹ N·m²/kg²
- r: distance between object centers (meters)
How to Use This Calculator
Weight Calculator Steps
- Enter your mass in kilograms.
- Choose a preset planet/moon gravity, or select custom.
- Click Calculate Weight to see weight in newtons and kilogram-force.
Force Calculator Steps
- Enter two masses in kilograms.
- Enter the center-to-center distance in meters.
- Click Calculate Force to compute gravitational attraction.
Practical Examples
If your mass is 70 kg, your Earth weight is roughly 686.7 N. On the Moon, the same mass would weigh only about 113.4 N. For engineering and space science, these conversions matter for structural design, launch planning, robotics, and astronaut safety.
The universal gravitation formula is also foundational for orbital mechanics. Satellites, space stations, and interplanetary probes rely on accurate gravity calculations to predict trajectories and fuel requirements.
Common Mistakes to Avoid
- Mixing up mass (kg) and weight (N).
- Entering distance as surface-to-surface instead of center-to-center.
- Using negative or zero distance values.
- Forgetting that small changes in distance can strongly affect force (inverse-square law).
Final Thoughts
A good gravity calculator is simple but powerful: it helps students learn physics, supports practical engineering estimates, and builds intuition for how motion in the universe works. Use the calculator above to experiment with different masses, gravities, and distances to better understand gravitational behavior.