buoyancy

buoyant +‎ -cy or buoy +‎ -ancy.

• (UK, US) IPA^(key): /ˈbɔɪ.ən.si/

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buoyancy (countable and uncountable, plural buoyancies)

1. (physics) The upward force on a body immersed or partly immersed in a fluid.
2. The ability of an object to stay afloat in a fluid.
3. (by extension) Resilience or cheerfulness.
   • 1834, L[etitia] E[lizabeth] L[andon], Francesca Carrara. […], volume III, London: Richard Bentley, […], (successor to Henry Colburn), OCLC 630079698, page 82:

     With how much lighter a step, with how much brighter an eye, did Francesca wander through the forest, even in the last desolation of autumn, than she did in all the bloom and buoyancy of spring!

• buoyant
• buoy
• buoy up

• Archimedes' principle