1A mechanical spring — a component made by coiling or twisting metal so it stores energy and returns to its original shape. Found everywhere: watches, cars, furniture, toys. The kanji 発条 / 弾機 / 撥条 are non-jōyō and almost never seen today. In writing, カタカナ バネ tends to be used in engineering/mechanical contexts, while ひらがな ばね is preferred in softer prose and figurative uses. The same word read as ぜんまい specifically refers to a wound mainspring (as in clocks and music boxes).
腕時計の中には精密なバネがいくつも組み込まれている。
Several precision springs are built into a wristwatch.
古いソファのばねがへたって、座るとお尻が沈み込む。
The springs in the old sofa have worn out, and you sink in when you sit down.
車のサスペンションに使われるバネは、走行中の衝撃を吸収する。
The springs in a car's suspension absorb shocks while driving.
ボールペンを分解したら、中から小さなバネが飛び出した。
When I took the ballpoint pen apart, a tiny spring popped out.
2Spring or bounce — the elastic, springy power in someone's legs or body that lets them move lightly. A figurative expression often used to describe athletes' leg strength or someone's youthful, agile movement, as in 「バネがある」 ("has spring/bounce") or 「ばねの利いた動き」 ("a movement with good spring"). This sense only applies to the readings ばね/バネ, not to ぜんまい.
あのバスケ選手は脚にバネがあって、軽々とリングまで届く。
That basketball player has real spring in his legs — he reaches the rim with ease.
彼の走り方には独特のばねがあって、見ていて気持ちがいい。
His running has a distinctive spring to it that's a pleasure to watch.
年とともに体のバネがなくなってきた気がする。
With age, I feel like my body is losing its spring.
3A springboard or driving impetus — something that provides momentum or a launching point toward growth, success, or a new challenge. Used in phrases like 「飛躍のばね」 ("a springboard for a leap forward") or 「悔しさをばねにする」 ("turn frustration into motivation"). Usually positive in tone, but commonly used for converting negative emotions into drive. Like sense 2, this only applies to the readings ばね/バネ.
若い頃の失敗を、その後の成長のばねにした。
I turned the failures of my youth into a springboard for later growth.
予選敗退の悔しさをバネに、来年こそ優勝を狙いたい。
Using my frustration at being knocked out in the prelims as fuel, I want to aim for the title next year.
海外留学が、彼女のキャリアを大きく伸ばすばねとなった。
Studying abroad became the springboard that propelled her career forward.