Empirical Earth · Gravity, Buoyancy & the Air

What you’d weigh on other worlds — gravity, not density

The claim

“Things fall because of density, not gravity.”

What is measured

What you weigh on a world is set by its surface gravity, g = G·M÷R 2, which depends on its mass and radius, not its density. The same person weighs about a sixth as much on the Moon, more than twice as much on Jupiter, and twenty-eight times as much on the Sun, while the gravitational constant G itself never changes.

What would show this is wrong

showing a world whose measured surface gravity follows its density rather than its mass and radius, like a low-density planet that leaves you nearly weightless, or two bodies of equal mass and radius but different surface gravity. None exists: every measured value across the Solar System obeys g = G·M÷R 2 to within measurement error.

Sources

  1. Surface gravity and density across the Solar System. NASA’s planetary fact sheet gives each body’s surface gravity, mean density and gravity ratio to Earth — e.g. Moon 1.6 m/s 2 (0.17×), Jup link
  2. Neutron-star surface gravity and density. A neutron star packs ~1.4 solar masses into a ~10 km radius, giving a surface gravity of ~10 12 –10 13 m/s 2 (more than 10 11 × Earth) and a density link
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