水裡的那股往上頂
這一組就是核心畫面本身，只是從兩個方向看同一件事：從水看，是水在推；從東西看，是它浮得起來。
noun · B2
The power of a liquid to push an object upwards so that it floats; in science, the upward force that a fluid puts on anything placed in it.
浮力
核心畫面
You can think of buoyancy as the push that water gives back. Hold a ball under the surface and you can feel the water working against your hand; let go, and the ball comes straight up. Every use of the word keeps two parts of that picture: there is something pressing down, and there is a steadier force answering it from below. Which part the word points at depends on the sentence — sometimes the push itself, sometimes the object that the push keeps up, and sometimes a person or a market that goes under for a while and then rises again.
buoyancy 可以想成水回推的那股力。把球按進水裡，你的手會感覺到水在頂回來。一放手，球就直接浮上去。這個字的每…更多收起
buoyancy 可以想成水回推的那股力。把球按進水裡，你的手會感覺到水在頂回來。一放手，球就直接浮上去。這個字的每一個用法，都留著這個畫面的兩半：一邊有東西在往下壓，另一邊有一股力穩穩地從下面頂回來。字指的是哪一半，要看句子。有時候指那股力本身。有時候指被頂住、所以會浮的那個東西。有時候指一個人或一個市場：先沉下去一陣子，然後又升回來。From the word’s history
Wiktionary derives buoyancy from buoyant plus -cy, or from buoy plus -ancy. A buoy is the marker that sits on the surface and will not stay pushed under; the suffix turns that behaviour into something you can name and measure.
Wiktionary 記 buoyancy 來自 buoyant（會浮的）加 -cy，或 buoy（浮標）加 -ancy。浮標就是那個永遠壓不下去、總是留在水面上的東西。字尾 -cy／-ancy 把這種行為變成一個名詞，於是「會浮」這件事就成了可以談、可以量的性質。
Wiktionary entry for buoyancy (kaikki extract, source_ref kaikki:3f6f69a190036ae4:926980649): From buoyant + -cy or buoy + -ancy.
Two branches
被壓下去又浮回來
水上的畫面被借去講看不見的東西。重點從「會浮」變成「壓不住」：先有一件事把人或數字壓下去，然後它自己又升回來。所以這一組的句子裡，幾乎一定找得到那個先前的低潮。
noun · C1
A cheerful, hopeful mood, together with the feeling that problems will not keep you down for long.
開朗；樂觀有韌性