Firmament dossier · Observation · 2 min read
Gravity or density?
Why things fall — and why some say "gravity" is unnecessary
The full text of this study is in Portuguese; the summary, key points and official view are in English.
Among researchers of the firmament, it is common to hear that there is no force called gravity: things fall or float because of density. A stone sinks in water and a cork floats; warm air rises and cold air sinks. For them, density and buoyancy would explain everything we see, and Newton’s gravity would be a hypothesis needed only to keep the oceans “stuck” to a moving ball. This dossier presents the argument, the classic experiments and the official answer.
Key points
- Archimedes (3rd century BC) described buoyancy: a submerged body receives a force equal to the weight of the fluid it displaces.
- Newton published the law of universal gravitation in 1687, in the Principia.
- The Cavendish experiment (1797–1798) measured the attraction between lead spheres on a torsion balance.
- In 1971, astronaut David Scott dropped a hammer and a feather on the Moon, during the Apollo 15 mission.
- In vacuum chambers, objects of different densities fall together.
What the official version says
For physics, density explains whether an object floats or sinks in a fluid, but not why it falls: buoyancy depends on gravity (B = ρ·V·g). In a vacuum, objects of different densities fall with the same acceleration, as has been shown in laboratories and on the Moon. The Cavendish experiment has been repeated many times, with different methods, and is used to measure the gravitational constant G.
Keep investigating
- Water always finds its level Lakes, canals and the movement's simplest question
- NASA, composite images and distrust The 1972 Blue Marble, the 2002 and 2012 mosaics and what can be checked
- Horizon, perspective and the boat that comes back with zoom What eyes and cameras show at a distance
Other languages: Português · Español
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