One way to hold this word: a weight hanging on a long string. Let it go and it swings to one side, then back to the other, then back again. Each swing takes about the same time and covers about the same ground. It is not travelling anywhere — it stays in one place and keeps crossing between two sides. Everything else the word does is that same weight with something else hung in its place: a price, a mood, or an electric current.
The word was taken into English in the 1720s from Latin ōscillō, meaning to swing, which comes from ōscillum, a swing. So the swinging picture is not a teaching invention — it sits in the word's own history.
這個字大約在一七二〇年代進入英文，來自拉丁文 ōscillō「擺盪」，而 ōscillō 又來自 ōscillum「一個鞦韆」。所以「來回擺盪」這個畫面不是後來想出來的比喻，它本來就在這個字的來歷裡。
Wiktionary 'oscillate' (packet evidence, source_ref kaikki:3f6f69a190036ae4:825976018:15825)
From the picture
數值與心情的來回
把線上掛的重物換成一個數字或一種感覺。來回的動作完全沒變，只是改在看不見的地方發生，所以句子還是要說出兩個端點：oscillate between A and B。
verb · C1
If an amount, a price, or a level oscillates, it keeps going up and down between a high point and a low point, instead of staying at one steady value.
上下波動
電流的來回（專業用法）
一樣是來回，只是發生在電線裡，而且快到看不見：電流往一個方向流，再翻過來往反方向流，一秒重複很多次。
verb · C2
When an electric current oscillates, it keeps changing direction — one way, then the other way — in a regular pattern, and it does this very many times each second.
（電流）振盪
verb · C1
To move from one side to the other and back again, over and over, in a regular repeating way.
來回擺動