Gravity Calculator
Frequently Asked Questions
What is the gravitational constant G and why does it matter?
G = 6.674 × 10⁻¹¹ N·m²/kg² is the universal gravitational constant that appears in Newton's formula F = Gm₁m₂/r². It determines the overall strength of gravity. Without G, the formula would give dimensionally inconsistent results. Its small value explains why gravity between everyday objects is imperceptibly weak.
What is the difference between mass and weight in gravity calculations?
Mass is the amount of matter in an object, measured in kilograms, and does not change with location. Weight is the gravitational force on that mass, measured in Newtons, and varies by planet. A 70 kg person weighs 686 N on Earth but only 113 N on the Moon, even though their mass stays exactly 70 kg everywhere.
How do I calculate how long it takes an object to fall a given distance?
Use the free-fall formula: time = √(2 × height / g), where g is the local gravitational acceleration. On Earth with g = 9.81 m/s², an object dropped from 20 meters takes √(2 × 20 / 9.81) ≈ 2.02 seconds to reach the ground. This assumes no air resistance — actual times are slightly longer due to drag.
Why does gravity decrease with altitude?
Newton's law shows gravitational acceleration g = GM/r², where r is distance from the planet's center. As altitude increases, r gets larger, so g decreases by the square of that distance. At 400 km altitude (ISS orbit), Earth's gravity is still about 88% of its surface value — astronauts feel weightless because they are in continuous free fall, not because gravity is absent.
Can I use this calculator for gravity between two small objects?
Yes, but the forces will be extremely tiny. Two 1 kg masses separated by 1 meter exert only about 6.67 × 10⁻¹¹ N on each other — far too small to measure without laboratory equipment. This is why we only notice gravity from massive bodies like Earth, the Moon, or the Sun in everyday life.
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