📚 Movement & Position | 运动与位置
This article covers the essential concepts of movement and position for Edexcel IGCSE Physics. You will learn to distinguish between scalar and vector quantities, calculate speed and acceleration, and interpret motion graphs with confidence. These fundamental topics appear in almost every exam paper, so mastering them is critical for achieving a high grade.
本文涵盖 Edexcel IGCSE 物理中运动与位置的核心概念。你将学会区分标量与矢量、计算速率与加速度，并自信地解读运动图像。这些基础性主题几乎出现在每份试卷中，掌握它们对于取得高分至关重要。
1. Distance vs Displacement | 距离与位移
Distance is a scalar quantity that describes how much ground an object has covered, regardless of direction. Displacement is a vector quantity that describes the object’s change in position, including direction. Both are measured in metres (m) in the SI system.
距离是标量，描述物体总共经过了多少路径，与方向无关。位移是矢量，描述物体位置的变化，并包含方向。两者在国际单位制（SI）中的单位均为米（m）。
For example, if a runner completes one lap of a 400 m track and returns to the starting point, the distance travelled is 400 m, but the displacement is zero because the final position is identical to the initial position.
例如，如果一名跑步者沿 400 米的跑道跑完一圈回到起点，则经过的距离为 400 米，但位移为零，因为末位置与初位置完全相同。
displacement = final position – initial position
位移 = 末位置 – 初位置
In exam questions, pay close attention to whether the question asks for distance or displacement. A question that asks for the distance travelled requires you to add all path lengths, while a question that asks for displacement requires you to consider only the straight line from start to finish.
在考试题目中，要特别注意题目问的是距离还是位移。如果题目要求”经过的距离”，你需要把所有路径长度相加；如果问的是”位移”，你只需考虑从起点到终点的直线变化。
2. Speed vs Velocity | 速率与速度
Speed is the distance travelled per unit time, and it is a scalar quantity. Velocity is the displacement per unit time, and it is a vector quantity. The SI unit for both is metres per second (m/s), though km/h is sometimes used in everyday contexts.
速率是单位时间内经过的距离，属于标量。速度是单位时间内的位移，属于矢量。两者的 SI 单位均为米每秒（m/s），日常中有时也使用千米每小时（km/h）。
The key difference is that velocity must include direction. A car travelling north at 20 m/s and a car travelling south at 20 m/s have the same speed but different velocities. In physics problems, velocities are written with direction or sign conventions, such as +20 m/s and -20 m/s along a chosen axis.
关键区别在于速度必须包含方向。一辆以 20 m/s 向北行驶的汽车和一辆以 20 m/s 向南行驶的汽车具有相同的速率，但速度不同。在物理题目中，速度需要标注方向或正负号，例如沿选定轴的 +20 m/s 与 -20 m/s。
To convert from km/h to m/s, divide by 3.6. For example, 72 km/h = 72 ÷ 3.6 = 20 m/s. This conversion appears frequently in examination questions, so memorise it.
将 km/h 换算为 m/s 时，除以 3.6。例如，72 km/h = 72 ÷ 3.6 = 20 m/s。这种换算在考试中经常出现，务必牢记。
3. Calculating Speed, Distance and Time | 计算速率、距离与时间
The fundamental equation linking speed, distance and time is:
连接速率、距离与时间的基本方程为：
speed = distance ÷ time
速率 = 距离 ÷ 时间
From this equation, we can rearrange to find distance or time:
由该方程可以变形求出距离或时间：
distance = speed × time and time = distance ÷ speed
距离 = 速率 × 时间 以及 时间 = 距离 ÷ 速率
Average speed is calculated using the total distance travelled divided by the total time taken. Instantaneous speed, on the other hand, is the speed at a specific moment, often measured with a speedometer. The speedometer of a car shows instantaneous speed, while a journey’s total distance divided by total time gives average speed.
平均速率等于总路程除以总时间。瞬时速率则是某一特定时刻的速率，通常用速度表测量。汽车速度表显示的是瞬时速率，而一段行程的总距离除以总时间得到的是平均速率。
When solving numerical problems, always check that your units are consistent. If distance is in kilometres and time is in hours, the speed will be in km/h. In IGCSE physics, it is usually safer to convert everything to metres and seconds before calculating.
解数值计算题时，务必检查单位是否一致。如果距离单位为千米、时间单位为小时，则速率单位为 km/h。在 IGCSE 物理中，通常建议先把所有量换算为米和秒再进行计算。
Consider a worked example: A cyclist travels 240 m in 30 seconds. The average speed is 240 ÷ 30 = 8 m/s. Now suppose the cyclist continues at this speed for another 2 minutes. The additional distance travelled is 8 × 120 = 960 m.
看一个例题：一名骑车人在 30 秒内行驶了 240 米。平均速率为 240 ÷ 30 = 8 m/s。假设该骑车人以此速率再骑行 2 分钟，则额外行驶的距离为 8 × 120 = 960 米。
4. Acceleration | 加速度
Acceleration is the rate of change of velocity. It is a vector quantity and is calculated using the equation:
加速度是速度的变化率，属于矢量，用以下公式计算：
acceleration = (final velocity – initial velocity) ÷ time
加速度 = （末速度 – 初速度）÷ 时间
The SI unit of acceleration is metres per second squared (m/s²). A positive acceleration means the object is speeding up in the chosen positive direction, while a negative acceleration, often called deceleration or retardation, means it is slowing down.
加速度的 SI 单位为米每二次方秒（m/s²）。加速度为正值表示物体沿选定正方向加速；加速度为负值（
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