📚 Year 9 OCR Science: Experiment & Practical Assessment Key Points | Year 9 OCR 科学：实验/实践考核要点
Practical assessments are a core component of Year 9 OCR Science, building the investigative skills needed for GCSE success. Understanding how to design fair tests, collect reliable data, and critically evaluate experiments is just as important as knowing the theory. This guide covers the key points you must master for your practical exams and coursework.
实践考核是 Year 9 OCR 科学的核心组成部分，培养 GCSE 成功所需的研究技能。理解如何设计公平测试、收集可靠数据以及批判性评价实验，与掌握理论知识同样重要。本指南涵盖你在实践考试和课程作业中必须掌握的关键要点。
1. Understanding Variables and Fair Testing | 理解变量与公平测试
In any experiment, the independent variable (IV) is the one you change, while the dependent variable (DV) is what you measure or observe. All other variables must be kept constant as control variables (CV) to ensure a fair test.
在任何实验中，自变量（IV）是你改变的变量，而因变量（DV）是你测量或观察的变量。所有其他变量必须作为控制变量（CV）保持不变，以确保公平测试。
For example, when investigating how temperature affects the rate of dissolving sugar, temperature (IV) is varied, the time taken to dissolve (DV) is recorded, and the volume of water and mass of sugar (CVs) are kept the same.
例如，在研究温度如何影响糖的溶解速率时，改变温度（IV），记录溶解所需时间（DV），同时保持水的体积和糖的质量（CV）相同。
Always list variables before starting the experiment and decide on a suitable range for the independent variable.
开始实验前务必列出所有变量，并决定自变量的合适范围。
2. Laboratory Safety and Risk Assessment | 实验室安全与风险评估
Safety is the first priority in any practical. You must wear safety goggles, tie back long hair, and tuck in loose clothing. Never eat or drink in the lab.
在任何实验中，安全是第一位。你必须佩戴护目镜，束好长发，并将宽松的衣物塞好。绝对不在实验室饮食。
A risk assessment identifies possible hazards (like hot apparatus, corrosive chemicals) and states precautions to reduce risk. For example, when heating with a Bunsen burner, use a heat-proof mat, keep flammable materials away, and know the location of the fire blanket.
风险评估识别可能的危险（如热仪器、腐蚀性化学品）并列出减少风险的预防措施。例如，使用本生灯加热时，要使用耐热垫，远离易燃物，并知晓灭火毯的位置。
Always check equipment for damage before use, and report any accidents immediately to your teacher.
使用前始终检查设备是否损坏，如有任何事故立即报告老师。
3. Making Accurate Measurements | 进行精确测量
Accurate measurements are crucial for reliable results. When using a measuring cylinder, read the volume at the bottom of the meniscus, with your eye level at the mark. For rulers and thermometers, always estimate one extra digit after the smallest scale division (e.g., 2.5 cm on a ruler marked in cm, but better to use mm ruler and estimate to 0.5 mm).
准确的测量对于可靠的结果至关重要。使用量筒时，在弯月面底部且视线与刻度齐平读取体积。对于尺子和温度计，总是在最小刻度之后估读一位（例如，在以厘米标记的尺子上读为2.5厘米，但最好使用毫米尺并估读到0.5毫米）。
Electronic balances should be tared (zeroed) before measuring mass. Repeat measurements and calculate the mean to improve reliability, but first exclude any anomalous readings (outliers that don’t fit the pattern).
电子天平在测量质量前应调零（去皮）。重复测量并计算平均值以提高可靠性，但首先排除任何异常读数（不符合模式的数据点）。
Use the most appropriate instrument for the job—e.g., a micrometer for very small lengths, a pipette for precise liquid volumes.
使用最合适的仪器——例如，用千分尺测量极小长度，用移液管量取精确液体体积。
4. Recording Data in Tables | 用表格记录数据
Data must be recorded in a clear table with ruled columns and rows. Each column heading must include the measured quantity and its unit, such as 'Time (s)' or 'Temperature (°C)'.
数据必须记录在带有横线行和列的清晰表格中。每个列标题必须包含测量量和单位，如“时间（s）”或“温度（°C）”。
Record data to the appropriate number of decimal places, consistent with the precision of the instrument. Use decimals, not fractions. A repeated readings column (e.g., Trial 1, Trial 2, Trial 3) shows that you collected multiple data sets.
记录数据时应保留与仪器精度一致的小数位数。使用小数而非分数。重复读数列（例如，试验1，试验2，试验3）显示你收集了多组数据。
If you calculate an average, include it in a separate column labelled 'Mean (unit)'. Anomalies should be bracketed or marked and not included in the average.
如果计算平均值，请将其放在标有“平均值（单位）”的单独列中。异常值应加括号或标记，并不纳入平均值的计算。
5. Drawing and Interpreting Graphs | 绘制与解读图表
Graphs allow you to visualise the relationship between variables. Always plot the independent variable on the x-axis and the dependent variable on the y-axis. Label axes with quantity and unit (e.g., Temperature (°C)).
图表让你直观地看到变量之间的关系。始终将自变量画在x轴上，因变量画在y轴上。用数量和单位标记坐标轴（例如，温度（°C））。
cale that uses more than half the graph paper and rises in equal increments (e.g., 2, 4, 6… not 3, 5, 7…). Plot points with a small, sharp cross '×'. Draw a line of best fit— or a straight line, based on the data trend. Do not connect dot-to-dot unless instructed.
选择使用超过一半图表的刻度，并以相等的增量递增（如2，4，6……而不是3，5，7……）。用尖细的小叉号“×”标记数据点。基于数据趋势画出最佳拟合线——平滑曲线或直线。除非特别要求，不要逐点连线。
Interpret the graph by describing the pattern: linear, directly proportional, inversely proportional, or no correlation. Use the line to make predictions within the data range (interpolation) and cautiously beyond (extrapolation).
通过描述图形模式来解读：线性、正比例、反比例或无相关性。利用拟合线在数据范围内进行预测（内插），并谨慎地进行范围外的推断（外推）。
6. Identifying and Minimising Errors | 识别并减少误差
There are two main types of error. Systematic errors shift all results by a fixed amount, often due to faulty equipment or poor technique (e.g., a zero error on a balance). Random errors cause scatter, arising from unpredictable changes (e.g., slight variations in reading a scale).
主要有两类误差。系统误差使所有结果偏移一个固定
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