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Gravitational constant G
Beginner
A tiny constant measured first by Cavendish.
G = 6.67×10⁻¹¹ N·m²/kg²G = 6.67×10⁻¹¹ N·m²/kg² sets the strength of gravity. It is tiny, which is why gravity is only noticeable for huge masses. Cavendish measured it in 1798 with a torsion balance.
Two 1 kg masses 1 m apart attract with 6.7×10⁻¹¹ N.
G is a constant everywhere, g is not.
In more detail
The gravitational constant G is about 6.67 × 10⁻¹¹ N m² kg⁻². It sets the strength of gravity and was first measured by Cavendish using a torsion balance.
Real-world uses
- G is needed to compute the mass of planets and stars from their orbits.
- Precision measurements of G are an active area of research.
- Precision gravity measurements and tests of general relativity rely on G, which must be known to a high accuracy.
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Frequently asked questions
Why is G so small?
Because gravity is extremely weak compared with electromagnetism at everyday scales.
Who measured G first?
Henry Cavendish, in 1798, using a torsion balance.
Why was G so hard to measure?
Gravity is extremely weak between laboratory-sized masses, so Cavendish needed a torsion balance to detect the tiny force.
Related topics in Gravitation & Orbits
Universal law of gravitation · Acceleration due to gravity · Variation of g with altitude · Variation of g with depth