🥢 光的折射：筷子在水里“折断”了🥢 Refraction: the chopstick that “snaps” in water
上一片里，光照到镜面会被弹回来。可要是光不是撞上镜子，而是斜着钻进水里呢？筷子看起来断了，鱼看起来变浅了——这一片看光怎么“拐弯”。Last leaf, light bounced off mirrors. But what if light doesn’t hit a mirror — what if it slips into water at an angle? Then a chopstick looks snapped and fish look shallower. This leaf is about how light bends.
第 1 步：筷子“断”了，光拐弯了Step 1: The chopstick “snaps” — light bends
先把最奇怪的现象看清楚：筷子明明没有折。Start with the strangest sight: the chopstick is not broken at all.
筷子伸进水里，在水面处看起来像被“折断”了。其实筷子笔直，是光从水里射向空气时拐了弯；眼睛顺着拐弯后的光线看过去，就把水下的部分“看歪”了。Push a chopstick into a glass of water and at the surface it looks “snapped”. The chopstick is perfectly straight — it’s the light leaving the water that bends. Your eyes follow the bent rays and see the underwater half in the wrong place.
好端端的光，为什么一进水就拐弯？But why would light suddenly bend when it enters water?
第 2 步：为什么光会拐弯Step 2: Why light bends at all
光在水里跑得比在空气里慢。斜着进入水面时，光线的一边先“踩进慢地”，整条光线就被拽着拐向法线——入射角越大，折射角也越大，但水里那一侧永远更靠近法线；垂直射入时两边同时减速，光不拐弯，笔直穿过。Light travels more slowly in water than in air. Coming in at an angle, one edge of the beam “steps into the slow zone” first, so the whole beam is dragged toward the normal. The bigger the angle of incidence, the bigger the angle of refraction — yet inside the water it always stays closer to the normal. Straight in? Both edges slow down together, and the light passes without bending at all.
这个“拐弯”在生活里会玩出什么花样？So what tricks does this bending play in real life?
第 3 步：海市蜃楼与“变浅”的水Step 3: Mirages and “shallower” water
沙漠里，贴地面的空气又热又稀，光一层一层地拐弯，把远处的绿洲“搬”到你眼前——这就是海市蜃楼。还有一个安全提醒：池水看起来比实际浅，是光骗了你的眼睛。千万别凭肉眼判断水深就往下跳。In the desert, air near the ground is hot and thin. Light bends layer by layer and carries a distant oasis right to your eyes — that’s a mirage. And a safety note: a pool looks shallower than it really is, because light fools your eyes. Never judge the depth by sight alone before jumping in.
🎮 你来调激光（30 秒）🎮 Your turn: aim the laser (30 seconds)
拖动滑块，把激光射入水中，看入射角和折射角一起怎么变；再过 4 关观察挑战。Drag the slider to shoot the laser into the water and watch both angles change together; then clear 4 observation challenges.
一句话记住它：光从一种介质斜射入另一种时会拐弯（折射）；垂直射入不拐弯；空气→水里，光线朝法线靠。Remember it in one line: light bends (refracts) when it crosses into another medium at an angle; straight in, no bend; going air→water it leans toward the normal.
斜射入水会拐弯，筷子“折断”、鱼“变浅”都是它干的Bending at the surface makes chopsticks “snap” and fish look shallower入射角越大，折射角也越大，但水里那侧总更靠近法线Bigger angle in → bigger angle out, but the water side always hugs the normal海市蜃楼 = 光在冷热不均的空气里一路拐弯；池水看起来比实际浅A mirage is light bending through hot and cool air; pools look shallower than they are
内容参考 OpenStax 等公开教材，多来源核对 · AI 生成、人工审核 · 发现错误欢迎指正，帮这片叶子长得更好。Based on OpenStax and other open textbooks, cross-checked across sources · AI-generated, human-reviewed · Spotted a mistake? Tell us — help this leaf grow.
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