📈 加速度：速度变化的快慢📈 Acceleration: how fast speed changes

上一片里，小火箭学会了用「速度」描述跑得多快。可它发现：有的车越跑越快，有的越跑越慢——速度自己也在变。这一片就看：速度变化的快慢，怎么量。 Last leaf, the little rocket learned to describe motion with speed. But speed itself changes — some things speed up, some slow down. This leaf measures how fast the speed itself changes.

第 1 步：加速度不是「快」，是「越变越快」Step 1: Acceleration is not “fast” — it's “getting faster”

先纠正一个误会：加速度大，不代表跑得快，它量的是速度的变化。First, clear up a mix-up: a big acceleration doesn't mean fast — it measures how the speed changes.

跑车与高铁起步对比：谁加速度大 — 跑车 5 秒从 0 加到 30 m/s，每秒加 6；高铁 20 秒才从 50 加到 60，每秒只加 0.5。高铁明明更快，加速度却小得多——因为比的是「每一秒速度变多少」。它的单位是 m/s²（米每二次方秒）：速度（m/s）再除以时间（s）。 The sports car goes 0 to 30 m/s in 5 s: +6 every second. The train takes 20 s to go 50 to 60: only +0.5 per second. The train is faster yet accelerates far less — because we compare the change per second. Its unit is m/s²: speed (m/s) divided by time (s).

那加速度在车速上长什么样？看看仪表盘。So what does acceleration look like on the dashboard?

第 2 步：指针猛爬 = 加速；往下掉 = 减速Step 2: Needle climbing = speeding up; sinking = slowing down

速度表指针快速爬升 — 指针 5 秒从 0 爬到 30 m/s，就是每秒 +6 m/s，写作 a = 6 m/s²，车在加速。如果指针每秒往下掉 4 格？那就是 a = -4 m/s²：负号不是「更小」，是「减速」，也就是刹车。a = 0 呢？指针不动，匀速行驶。 The needle sweeps from 0 to 30 m/s in 5 s — that's +6 m/s each second, written a = 6 m/s²: speeding up. If the needle sinks 4 notches every second, then a = -4 m/s²: the minus sign means slowing down, i.e. braking. And a = 0 keeps the needle still — steady speed.

有没有一眼看穿加速度大小的办法？把它画成图。Is there a way to see acceleration at a glance? Draw it.

第 3 步：v-t 图上，越陡加速度越大Step 3: On a v-t graph, steeper means bigger acceleration

v-t 图上陡缓两条线 — 把速度随时间画成图：陡的那条线，速度涨得猛，加速度大；缓的那条，速度慢慢涨，加速度小。线往下斜？速度在掉，那就是减速。以后看到 v-t 图，先看陡不陡，加速度多大心里就有数了。 Plot speed against time: the steep line gains speed fast — large acceleration; the gentle one gains slowly — small acceleration. A line sloping down means speed is dropping: slowing down. On any v-t graph, check the steepness first to read the acceleration.

🎮 你来当试车员（30 秒）🎮 Your turn: test driver (30 seconds)

先拖动油门滑块、点「点火」，看车速每秒怎么变；再完成 4 个挑战。Drag the throttle, hit “Ignite” and watch the speed change each second — then pass 4 challenges.

一句话记住它：加速度 = 速度每秒的变化量。不是「快」，是「越变越快」；正号加速，负号减速，a = 0 匀速。 Remember it in one line: acceleration = how much speed changes each second. Not “fast”, but “getting faster” — positive speeds up, negative slows down, zero holds steady.

加速度 = 每秒速度变化多少，单位 m/s²；跑车猛不猛看它，不看最高速Acceleration = speed change per second, in m/s²; read it — not top speed — to judge a launch a > 0 越来越快；a < 0 越来越慢（刹车）；a = 0 匀速a > 0 speeds up; a < 0 slows down (braking); a = 0 is steady v-t 图上，线越陡加速度越大；向下斜就是减速On a v-t graph, steeper = larger acceleration; sloping down = slowing

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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.