📚 KS3 CIE Distance-Time Graphs: Mark Scheme Essentials | KS3 CIE 距离-时间图：评分标准要点
Distance-time graphs are a core part of the KS3 CIE science syllabus, and examiners use a consistent mark scheme to award marks for reading, interpreting and calculating from these graphs. In this revision guide, you will learn exactly what the mark scheme expects, how to structure answers, and which keywords and units earn full marks.
距离-时间图是 KS3 CIE 科学课程的核心内容，考官会依据统一的评分标准对读图、解释和计算进行给分。在本复习指南中，你将准确了解评分标准的要求、如何组织答案，以及哪些关键词和单位能获得满分。
1. What a Distance-Time Graph Shows | 距离-时间图表示什么
A distance-time graph plots distance travelled on the vertical y-axis against time taken on the horizontal x-axis. The mark scheme rewards answers that state this relationship clearly, for example ‘distance is plotted against time’.
距离-时间图将行驶距离绘制在纵轴（y 轴）上，将所用时间绘制在横轴（x 轴）上。评分标准奖励能清楚表述这一关系的答案，例如“距离随时间变化”。
In CIE mark schemes, you may be asked to identify which axis shows distance and which shows time. Always check the labels and units on both axes before answering, because using the wrong axis can cost you the first mark.
在 CIE 评分标准中，可能会要求你判断哪个轴表示距离、哪个轴表示时间。答题前一定要先查看两个轴上的标签和单位，因为用错坐标轴可能会丢掉第一分。
Examiners want precise language. Writing ‘the graph shows how far something goes’ is too vague. Instead, say ‘the y-axis shows distance from the start and the x-axis shows time elapsed’.
考官要求精确的语言。写“这张图显示物体走了多远”太模糊。相反，应该说“y 轴表示距起点的距离，x 轴表示经过的时间”。
2. Reading Values from the Axes | 从坐标轴读取数值
To read a value, draw a vertical line from a point on the graph down to the time axis, or a horizontal line across to the distance axis. Mark schemes award one mark for correct reading of the axis, even if the unit is written separately.
读取数值时，从图上的某一点向下画一条垂线到时间轴，或画一条水平线到距离轴。即使单位单独书写，评分标准也会为正确读取坐标轴给一分。
If the scale is not in steps of 1, you must count the subdivisions carefully. For example, if each large square represents 10 m, a point halfway across a square represents 5 m.
如果比例尺不是以 1 为单位，你必须仔细数出小格。例如，如果每个大格代表 10 m，那么一个点位于大格中间就代表 5 m。
Do not forget to include the unit when you write down a reading. A mark scheme may show a point for ’25’ and a separate point for ‘m’, so writing ’25 m’ is safer than writing just ’25’.
写下读数时不要忘记带上单位。评分标准可能会给“25”一分，再给“m”一分，因此写“25 m”比只写“25”更稳妥。
3. Gradient Equals Speed | 斜率等于速度
The gradient (slope) of a distance-time graph gives the speed of the object. The steeper the slope, the greater the speed. This is one of the most frequently credited mark scheme points.
距离-时间图的斜率（坡度）表示物体的速度。坡度越陡，速度越大。这是评分标准中最常给分的要点之一。
You should use the phrase ‘the gradient represents speed’ rather than just ‘the line goes up’, because mark schemes look for the correct scientific keyword.
你应该使用“斜率代表速度”这一表述，而不只是说“线向上走”，因为评分标准要求使用正确的科学关键词。
Mathematically, the gradient is calculated as the vertical change divided by the horizontal change. On a distance-time graph this is written as:
数学上，斜率等于垂直变化量除以水平变化量。在距离-时间图上，这可以写成：
gradient = rise ÷ run = Δd ÷ Δt
Here, Δd means the change in distance and Δt means the change in time. Using this method earns a method mark even if you later make a small arithmetic error.
这里，Δd 表示距离的变化量，Δt 表示时间的变化量。使用这种方法即使后来出现小的计算错误，也能得到方法分。
4. Horizontal Line: Stationary Object | 水平线：静止物体
A horizontal line on a distance-time graph means the object is stationary, because distance is not changing while time continues. Mark schemes typically award one mark for ‘stationary’ or ‘not moving’ and another for saying ‘distance remains constant’.
距离-时间图上的水平线表示物体处于静止状态，因为时间在继续但距离没有变化。评分标准通常给“静止”或“不移动”一分，给“距离保持不变”另一分。
Common wrong answers include ‘the object is moving slowly’ or ‘the object is moving at a constant speed’. These do not receive credit because a horizontal line has zero gradient, so speed is zero.
常见错误答案包括“物体在缓慢移动”或“物体在匀速运动”。这些答案不得分，因为水平线的斜率为零，所以速度为零。
If a question asks ‘what does the flat part of the graph show?’, answer with both the measurement and the scientific meaning: ‘the distance is not changing, so the object is stationary’.
如果题目问“图的水平部分表示什么？”，回答时要同时给出测量结果和科学含义：“距离没有变化，所以物体是静止的”。
5. Steepness and Comparing Speeds | 陡峭程度与速度比较
When comparing two lines on the same axes, the steeper line represents the faster object. The mark scheme expects you to compare gradients, not just say ‘one is higher’ unless that directly refers to steepness.
在同一坐标系中比较两条线时，较陡的线代表较快的物体。评分标准希望你能比较斜率，而不只是说“一条线更高”，除非这直接表示陡峭程度。
For example, if line A has a steeper slope than line B, you should write ‘A moves faster than B because A has a greater gradient’. A mark may be lost if you only say ‘A is ahead’.
例如，如果 A 线比 B 线更陡，你应该写“A 比 B 移动得快，因为 A 的斜率更大”。如果你只说“A 在前面”，可能会丢分。
If two lines are parallel on a distance-time graph, they have the same gradient. This means both objects are moving at the same speed, even if one has travelled a greater distance.
如果距离-时间图上的两条线互相平行，它们具有相同的斜率。这意味着两个物体以相同的速度运动，即使其中一个行驶的距离更远。
6. Straight Sloping Line: Constant Speed | 倾斜直线：匀速运动
A straight sloping line on a distance-time graph indicates constant speed. The distance increases by equal amounts in equal time intervals, so the gradient does not change.
距离-时间图上的倾斜直线表示匀速运动。距离在相等的时间间隔内增加相等的量，因此斜率不变。
When asked to describe the motion, the mark scheme often gives one mark for ‘constant speed’ and another for quoting the value if calculated. Always state that the speed is constant before giving a numerical value.
当要求描述运动时，评分标准通常给“匀速”一分，如果计算出数值再给一分。一定要先说明速度是恒定的，再给出数值。
For instance, a correct answer might be: ‘Between 0 s and 10 s the object moves at a constant speed of 4 m/s.’ This includes both the motion type and the value with its unit.
例如，一个正确答案可能是：“在 0 s 到 10 s 之间，物体以 4 m/s 的恒定速度运动。”这同时包含了运动类型和带单位的数值。
7. Curved Line: Acceleration and Deceleration | 曲线：加速与减速
A curve on a distance-time graph means the speed is changing. If the curve gets steeper, the object is accelerating (speeding up). If the curve gets less steep, the object is decelerating (slowing down).
距离-时间图上的曲线表示速度正在变化。如果曲线越来越陡，物体在加速（越来越快）。如果曲线越来越平缓，物体在减速（越来越慢）。
In KS3 CIE mark schemes, you may be asked to identify which part of a curved graph shows acceleration and which shows deceleration. Use the terms ‘gradient is increasing’ and ‘gradient is decreasing’ to secure marks.
在 KS3 CIE 评分标准中，可能会要求你指出曲线的哪一部分表示加速、哪一部分表示减速。使用“斜率在增大”和“斜率在减小”这些术语可以确保得分。
A curve that becomes vertical would mean an infinite speed, which is not physically possible for ordinary objects. In practice, all curved sections on KS3 graphs show gradual speeding up or slowing down.
变成垂直的曲线意味着无限大的速度，这对普通物体来说在物理上是不可能的。实际上，KS3 图中的所有曲线段都表示逐渐加速或逐渐减速。
8. Calculating Speed from a Graph | 从图中计算速度
To calculate speed from a straight-line section, choose two points on the line and use the formula: speed = distance ÷ time, or speed = change in distance ÷ change in time. Mark schemes award one mark for the correct method and one mark for the correct answer with units.
要从直线段计算速度，在线上选择两个点，并使用公式：速度 = 距离 ÷ 时间，或速度 = 距离变化量 ÷ 时间变化量。评分标准给正确的方法一分，给正确的答案和单位一分。
speed = distance ÷ time
If the graph shows a distance of 100 m covered in 20 s, then speed = 100 ÷ 20 = 5 m/s. You must include the unit m/s; a bare number without units usually loses a mark.
如果图显示 100 m 的距离在 20 s 内完成，则速度 = 100 ÷ 20 = 5 m/s。你必须写上单位 m/s；没有单位的数字通常会丢一分。
Always show your working clearly. Write the formula, substitute the numbers, and then give the answer. This means if your final answer is wrong, you can still earn method marks.
一定要清楚地展示你的计算过程。写出公式，代入数字，然后给出答案。这样即使最终答案错误，你仍然可以获得方法分。
9. Common Mark Scheme Command Words | 常见评分标准指令词
CIE mark schemes use command words such as ‘state’, ‘describe’, ‘calculate’ and ‘explain’. Each requires a different depth of answer.
CIE 评分标准使用诸如“state（陈述）”、“describe（描述）”、“calculate（计算）”和“explain（解释）”等指令词。每种指令词要求不同的答题深度。
| Command word | Meaning | Example for distance-time graph |
|---|---|---|
| State | Give a short answer without explanation | State the speed shown by the horizontal line. Answer: 0 m/s |
| Describe | Say what
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