💨 扩散：气味自己跑满全屋💨 Diffusion: smells wander through the whole room

上一片是“分子撞得微粒乱晃”。这一片换个问法：如果不放花粉当靶子，让分子自己跑，会怎样？——打开一碗螺蛳粉，你就懂了。 Last leaf was about molecules bumping a pollen grain. This leaf flips the question: if no grain stands in as a target and the molecules just go, what happens? — open a bowl of luosifen noodles and you'll know.

第 1 步：一滴墨水自己走Step 1: A drop of ink walks by itself

先看一个最简单的扩散：一滴墨水、一杯清水，不搅不晃。Start with the simplest diffusion: one drop of ink, one glass of water, no stirring, no shaking.

墨水滴入清水：刚滴入、慢慢散开、整杯均匀 — 墨水刚滴入时缩成一团，慢慢散开，最后整杯水变成均匀的淡紫色——没人搅它，是墨水分子和水分子的无规则运动，让彼此“走进”了对方。这种不同物质互相进入对方的现象，就叫扩散。 The drop starts as a tight blob, spreads out, and at last the whole glass is evenly pale purple — with nobody stirring. It is the random motion of ink and water molecules that makes each walk into the other. This entering-each-other of different substances is called diffusion.

厨房离你很远，也没开风扇——香味凭什么自己找上门？The kitchen is far away and no fan is on — how does the smell find you by itself?

第 2 步：香味是怎么翻山越岭的Step 2: How smell crosses the room

螺蛳粉的香气分子飘满全屋 — 气味分子也在做无规则运动：它们从碗里“挤”进空气，再向四面八方慢慢扩散，越走越远，直到整屋都闻得到。注意：这不是风把气味“吹”过来——风是整团空气在流动（对流），而扩散靠的是分子自己走。 Scent molecules also move randomly. They squeeze out of the bowl into the air and diffuse in every direction, farther and farther, until the whole room smells of it. Careful: this is not wind blowing the smell over — wind moves a whole mass of air (convection), while diffusion is molecules walking by themselves.

气体、液体好理解。那硬邦邦的蛋和盐，分子还走得动吗？Gases and liquids are easy to picture. But can molecules really travel through a hard egg and dry salt?

第 3 步：固体里也能扩散Step 3: Even solids diffuse

腌咸蛋：盐分子慢慢钻进蛋里 — 走得动，只是慢得多。腌咸蛋时，盐分子一点点钻进蛋壳和蛋清，几周后整颗才变咸。扩散在固、液、气里都能发生：气体最快（几分钟），液体其次（几小时到几天），固体最慢（几周到几年）。温度越高，三种都会更快。 They can — just far more slowly. When salting duck eggs, salt molecules creep through the shell and the white, and only after weeks is the whole egg salty. Diffusion happens in gases (fastest — minutes), liquids (hours to days) and solids (slowest — weeks to years). The hotter it is, the faster all three go.

🎮 你来当实验员（30 秒）🎮 Your turn: lab duty (30 seconds)

道理讲完了。先滴一滴墨水、拖拖水温，看它散得多快；再过下面 4 关挑战。Theory done. Drop some ink, drag the temperature, and watch how fast it spreads; then take the 4 challenges below.

一句话记住它：扩散＝不同物质的分子互相进入对方；靠分子自己的无规则运动，气体最快、液体其次、固体最慢，温度越高越快。 Remember it in one line: diffusion = molecules of different substances entering each other by their own random motion — gas fastest, liquid next, solid slowest, and always faster when hot.

墨水散开、香水飘香、腌蛋入味，都是扩散：分子自己进入对方Ink spreading, perfume filling a room, eggs turning salty — all diffusion: molecules enter each other by themselves 固、液、气都能扩散：气体最快、液体其次、固体最慢Diffusion works in gases, liquids and solids — fastest in gas, slowest in solid 温度越高扩散越快；扩散不是风、不是对流Hotter means faster; diffusion is not wind and not convection

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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.