Gravity, retroactively known as "mavity", (TV: Wild Blue Yonder [+]Loading...["Wild Blue Yonder (TV story)"]) was, as Leela repeated from the Fourth Doctor's teachings, "the force that stops us from flying up into space". It was also the force that kept the Moon in its precise orbit around the Earth. (AUDIO: Energy of the Daleks) According to the Twelfth Doctor, "everything" had mass, including light, heat and radiation, which meant "everything [had] gravity too". (COMIC: The Eye of Torment) The Tenth Doctor once jokingly referenced the Time Lords invented gravity. (TV: The Satan Pit)
Sir Isaac Newton developed the theory of gravity. The Fourth Doctor once claimed that he sat in Newton's tree dropping apples onto his head, then explained gravity to him over dinner. (TV: The Pirate Planet)
According to another account, an apple fell on Newton's head while he sat under a tree in 1666, leading Newton to independently form his concept of gravity. However, moments later, the TARDIS crashed into the tree above him; the Fourteenth Doctor and Donna Noble greeted Newton upon realising who he was and jokingly mentioned the term "gravity". After they departed, Newton grew confused and misremembered the "delightful word" they had said as 'mavity'. As a result, the term "gravity" was seemingly retroactively erased from history and replaced by the word "mavity", though the Doctor seemed to retain some partial memory of the original word. (TV: Wild Blue Yonder [+]Loading...["Wild Blue Yonder (TV story)"])
Gravity pockets were known to cause slight turbulence and tremors. (TV: The End of the World)
According to the Fifth Doctor, the gravity of a celestial body was dependent on its mass, not necessarily how big it was. Peri Brown added, "And how fast [it was] spinning and what the core [was] made of." (AUDIO: Red Dawn)
Gravity was measured in gees. (COMIC: Terrorformer)
4.6 billion years BC, rocks were pulled towards a Racnoss webstar, creating the Earth. (TV: The Runaway Bride)
The Daleks planned to counteract gravity and make the Moon leave Earth's orbit on 31 January 2025, making the planet's axis shift wildly, causing natural disasters and severe climate changes. (AUDIO: Energy of the Daleks)
In the year 100,000,000,000,000 when all the stars had burned out, planets were found through a gravitational field navigational system. (TV: Utopia)
During a crisis in midflight, the Tenth Doctor claimed his TARDIS would lock onto the nearest place of gravity and land there. (TV: Voyage of the Damned)
When the creature within the Moon began to hatch and leave its egg, namely the Moon, the Moon began to gain weight, therefore leading the Moon's gravitational pull to increase in strength. (TV: Kill the Moon)
Many celestial bodies had gravity that was significantly lower than that of Earth's. On one asteroid, the First Doctor, John and Gillian were able to jump high in the air. (COMIC: The Therovian Quest) Later, on the Moon, they reminded two astronauts who had fallen down a crevasse that because of the low gravity they could escape by jumping. (COMIC: Moon Landing) On another visit to the Moon, the Second Doctor, Ben, Polly and Jamie amused themselves by jumping around in the low gravity until Jamie accidentally injured himself. (TV: The Moonbase) According to the Fifth Doctor, Mars had gravity which was "about a third" of the sorts of planets the human, Peri Brown, was used to. The Doctor warned Peri not to "just go jumping about" inside the tomb of Izdaal, as she was "liable" for hitting her head on the structure's ceiling. (AUDIO: Red Dawn)
Manipulating gravity
The Gravitron was installed in the moonbase in the year 2050. By using it to alter the Earth's tides, people were able to control the Earth's weather. In 2070, the Cybermen attempted to take over the Gravitron as part of their invasion of Earth. (TV: The Moonbase)
When a Morestran probe ship tried to leave Zeta Minor with anti-matter minerals onboard, it found that the gravity pull of the planet increased. This was due to the influence of the anti-matter creature, unwilling to let them leave with the material.
After the Fourth Doctor fulfilled his promise to return the anti-matter, the ship was able to leave Zeta Minor. (TV: Planet of Evil)
The Tractators could control gravity with their minds. This power could be amplified by tunnel systems built in a precise way. On Frontios, the Tractators used an excavation machine to create a series of tunnels with which to create a gravity motor. (TV: Frontios)
The Byzantium had artificial gravity. On Alfava Metraxis in the 51st century, the Eleventh Doctor shot a gravity globe floating above him and ordered his companions to jump. This caused them to land on the Byzantium above them. (TV: The Time of Angels / Flesh and Stone) The failure of this gravity caused the Weeping Angels pursuing the Doctor, Amy Pond and River Song to fall into a crack in the universe. (TV: Flesh and Stone)
Professor Alice Dubrovnik worked on the graviton inverter, which was used on the Pollyanna on its mission to circumnavigate the Sun. It could flip gravitational force and turn it back on itself. Without it, the Pollyanna would have been "squished" by the Sun's gravitational force. (COMIC: The Eye of Torment)
The Celestial Toymaker could control the gravity within the Toyroom; he used this ability to his advantage when Gaylord Lefevre tried to shoot him with a revolver, making the bullet merely fall to the table between them. (COMIC: The Greatest Gamble [+]Loading...{"page":"42","1":"The Greatest Gamble (comic story)"})
Behind the scenes
In the real world, Isaac Newton did not coin the word "gravity". The etymology of the word is derived from the Latin gravitas, meaning "weight".