📚 Making Parachutes: Investigating Air Resistance and Gravity | 制作降落伞：探究空气阻力与重力
A parachute slows down a falling object by increasing air resistance. In KS3 Science, making parachutes is a practical way to explore forces, drag, and fair testing. This article explains how to design, carry out, and evaluate a parachute investigation for CIE KS3.
降落伞通过增大空气阻力来减慢下落物体的速度。在 KS3 科学课中，制作降落伞是探究力、阻力和公平实验的实践活动。本文将讲解如何为 CIE KS3 设计、实施和评估降落伞实验。
1. What is a Parachute? | 什么是降落伞？
A parachute is a large canopy made of light material, such as plastic, fabric, or paper. When attached to a load, it opens during descent and traps air underneath. This creates a large upward drag force that opposes the downward pull of gravity. Without a parachute, a falling object accelerates quickly; with one, it reaches a much lower terminal velocity.
降落伞是由塑料、布料或纸等轻质材料制成的大型伞面。它与重物相连，下降时展开并兜住伞下的空气。这会产生一个向上的巨大阻力，与向下的重力相对抗。没有降落伞时，下落物体加速很快；有降落伞时，它会达到低得多的终端速度。
In everyday language, a parachute 'catches' air. Scientifically, the canopy increases the surface area that collides with air molecules, so more upward force is produced. This is why even a light plastic sheet can slow a metal washer.
日常语言中说降落伞会 ' 兜住 ' 空气。科学地说，伞面增大了与空气分子碰撞的表面积，因此产生更大的向上力。这就是为什么即使是一片轻塑料膜也能减慢金属垫圈的下落。
2. Forces Acting on a Parachute | 作用在降落伞上的力
Two main forces act on a falling parachute: weight (gravity) pulling down and air resistance (drag) pushing up. Weight is caused by the mass of the parachute and its payload. Air resistance depends on surface area, shape, speed, and air density. When drag equals weight, the parachute stops accelerating and falls at a steady speed called terminal velocity.
作用在降落伞上的主要力有两个：重力向下拉，空气阻力向上推。重力由降落伞和载荷的质量引起。空气阻力取决于表面积、形状、速度和空气密度。当阻力等于重力时，降落伞不再加速，以稳定速度下落，这个速度称为终端速度。
You can write the weight force as:
重力可以写作：
W = m × g
where W is weight in newtons, m is mass in kilograms, and g is 10 N/kg on Earth. The drag force is not constant; it increases as the parachute falls faster or uses a larger canopy area.
其中 W 是重力，单位是牛顿；m 是质量，单位是千克；g 在地球上为 10 N/kg。阻力不是恒定的，当降落伞下落更快或伞面面积更大时，阻力会增大。
3. Aim and Hypothesis | 实验目的与假设
The aim is to investigate how the size of a parachute canopy affects the time it takes to fall to the ground. A possible hypothesis is: 'If the canopy area is larger, then the parachute will take longer to land because air resistance increases.' The independent variable is canopy size, while the dependent variable is descent time.
实验目的是探究降落伞伞面大小如何影响其落地时间。可提出的假设是：' 如果伞面面积越大，降落伞落地时间越长，因为空气阻力增大。' 自变量是伞面大小，因变量是下降时间。
A hypothesis should be testable and based on scientific reasoning. It is not simply a guess. For example, linking area to air resistance and then air resistance to slower motion shows clear cause and effect.
假设应当可检验并基于科学推理，而不是随便猜测。例如，将面积与空气阻力联系，再将空气阻力与更慢的运动联系，就体现了清晰的因果关系。
4. Variables in the Experiment | 实验变量
Independent variable: canopy surface area, changed by using squares of different side lengths e.g. 20 cm, 30 cm, 40 cm, 50 cm. Dependent variable: time taken to fall a fixed height. Control variables: mass of the load, length of strings, material of canopy, drop height, and shape of canopy. Controlling these makes the test fair.
自变量：伞面表面积，通过使用不同边长的正方形来改变，例如 20 厘米、30 厘米、40 厘米、50 厘米。因变量：从固定高度下落所需的时间。控制变量：负载质量、绳子长度、伞面材料、下落高度和伞面形状。控制这些变量使实验公平。
If you do not control the mass, a heavier load might fall faster even with the same canopy. That would make your results invalid because two variables would change at once. Always keep the same load and the same drop height.
如果不控制质量，较重的负载即使伞面相同也可能下落更快。这会使结果无效，因为同时改变了两个变量。务必保持相同的负载和相同的下落高度。
5. Materials and Equipment | 材料与设备
- Plastic bags or bin liners, scissors, ruler, string, small masses or washers, stopwatch, metre ruler or tape measure, electronic balance, sticky tape.
- 塑料袋或垃圾袋、剪刀、尺子、细绳、小质量块或垫圈、秒表、米尺或卷尺、电子天平、胶带。
- You may also use a clamp stand or step ladder to ensure a fixed drop height and a clear landing area.
- 你还可以使用铁架台或梯子保证固定的下落高度，并准备一个无障碍的着陆区。
Choose similar plastic bags so the material thickness is constant. Cut squares carefully, because uneven edges can change how the canopy opens and affect air resistance.
选择相似的塑料袋以保持材料厚度一致。裁剪正方形时要仔细，因为边缘不齐会改变伞面展开方式并影响空气阻力。
6. Method: Step by Step | 实验步骤
1. Cut a square canopy from the plastic bag. 2. Attach four equal lengths of string to the corners with tape. 3. Tie the free ends of the strings to the mass. 4. Measure and record the mass of the load. 5. Drop the parachute from a marked height and time its fall. 6. Repeat three times for each canopy size and calculate the average time.
1. 从塑料袋剪出一个正方形伞面。2. 用胶带在四角各系一根等长细绳。3. 将绳子的自由端绑在质量块上。4. 测量并记录负载质量。5. 从标记高度释放降落伞并计时。6. 每个伞面尺寸重复三次，计算平均时间。
Start the stopwatch when the parachute leaves your hand, and stop it when the load touches the floor. The same person should time all drops if possible to reduce reaction-time error.
当降落伞离开手的瞬间开始计时，当负载接触地面时停止计时。如果可能，应由同一个人完成所有计时，以减少反应时间误差。
Repeat trials are essential. One drop can be affected by a random gust of air or a canopy that does not open fully. Averaging three or more trials reduces the effect of random errors.
重复试验非常重要。一次下落可能受到随机气流或伞面未完全展开的影响。取三次或更多次试验的平均值可以减少随机误差的影响。
7. Recording Results: Data Table | 记录结果：数据表
Use a table with columns: canopy side length (cm), canopy area (cm²), time 1 (s), time 2 (s), time 3 (s), average time (s). For example, side length 20 cm gives area 400 cm²; 30 cm gives 900 cm²; 40 cm gives 1600 cm²; 50 cm gives 2500 cm². Include units in headings.
使用表格记录，栏目包括：伞面边长（cm）、伞面面积（cm²）、时间 1（s）、时间 2（s）、时间 3（s）、平均时间（s）。例如边长 20 cm 对应面积 400 cm²；30 cm 对应 900 cm²；40 cm 对应 1600 cm²；50 cm 对应 2500 cm²。表头要写单位。
| Side length (cm) | Area (cm²) | Trial 1 (s) | Trial 2 (s) | Trial 3 (s) | Average time (s) |
| 20 | 400 | 1.1 | 1.3 | 1.2 | 1.2 |
| 30 | 900 | 1.7 | 1.9 | 1.8 | 1.8 |
| 40 | 1600 | 2.2 | 2.4 | 2.3 | 2.3 |
| 50 | 2500 | 2.5 | 2.8 | 2.6 | 2.6 |
Always calculate averages to one more decimal place than the raw data if possible. In the example above, time 1, time 2 and time 3 are recorded to one decimal place, so the average is also written to one decimal place.
如果可能，平均值通常比原始数据多保留一位小数。在上述示例中，时间 1、时间 2 和时间 3 记录到一位小数，因此平均值也保留一位小数。
8. Graph and Analysis | 图表与分析
Plot average time on the y-axis against canopy area on the x-axis. The expected shape is a curve rising and then levelling off because drag becomes large but time cannot increase forever. Describe the trend: as area increases, descent time increases. Use the graph to identify anomalies and compare repeats.
将平均时间画在 y 轴，伞面面积画在 x 轴。预期曲线先上升后趋于平缓，因为阻力变大，但降落时间不可能无限增加。描述趋势：面积增大时下降时间增加。利用图表识别异常数据并比较重复实验。
If one point lies far from the line of best fit, it may be an anomaly. Do not ignore it; try to explain it. Perhaps the canopy did not open properly in that trial, or the stopwatch was started late.
如果某个点远离最佳拟合线，它可能是异常数据。不要忽略它，而要尝试解释原因。可能是该次实验中伞面没有正常展开，或者秒表启动晚了。
For a fair comparison, the line graph must start the x-axis at zero. If the axis is broken, differences can appear larger than they really are, which is misleading.
为了公平比较，折线图的 x 轴必须从零开始。如果坐标轴被截断，差异会显得比实际更大，从而产生误导。
9. Conclusion and Evaluation | 结论与评估
State whether the results support the hypothesis. Refer to data, e.g. 'The average time increased from 1.2 s at 400 cm² to 2.6 s at 2500 cm², so larger canopies fall more slowly.' Evaluate sources of error such as release timing, canopy not opening fully, or air currents. Suggest improvements like using a video timer or releasing with a mechanism.
说明结果是否支持假设。引用数据，例如 ' 平均时间从 400 cm² 时的 1.2 秒增加到 2500 cm² 时的 2.6 秒，因此更大的伞面下落更慢。' 评估误差来源，如释放计时不准、伞面未完全展开或气流影响。提出改进方法，如使用视频计时或机械释放装置。
A good evaluation considers accuracy and reliability. Accuracy asks how close results are to the true value, while reliability asks whether repeats are consistent. If the three trials for each canopy are close together, the data are reliable.
好的评估要同时考虑准确性和可靠性。准确性指结果与真实值的接近程度，可靠性指重复实验是否一致。如果每个伞面的三次试验数据接近，就说明数据可靠。
You could also calculate the range of the repeats. A small range shows random errors are small. If the range is large, identify and control more variables, or increase the number of trials.
你还可以计算重复数据的极差。极差小说明随机误差小。如果极差大，应找出并控制更多变量，或增加试验次数。
10. Real-World Applications | 实际应用
Parachutes are used in skydiving, emergency evacuation from aircraft, spacecraft landing capsules, and cargo drops. In all cases, engineers design canopy area, material, and vent holes to control drag and stability. A larger canopy is used for heavy loads to keep landing speed safe.
降落伞用于跳伞、飞机紧急逃生、航天器着陆舱和货物空投。工程师设计伞面面积、材料和排气孔来控制阻力和稳定性。重型载荷使用更大伞面以保持安全着陆速度。
Spacecraft returning to Earth use multiple parachutes and retrorockets. Air resistance alone is not enough to slow a heavy capsule from orbital speed, so extra drag devices are staged.
返回地球的航天器使用多个降落伞和反推火箭。仅靠空气阻力不足以使重型返回舱从轨道速度减慢，因此会分级使用额外的减速装置。
Understanding parachute forces also helps engineers design umbrellas, airbags, and even seeds that spin as they fall. Rotating seeds such as sycamore use drag to fall more slowly, which gives the wind more time to carry them away from the parent tree.
理解降落伞受力还有助于工程师设计雨伞、安全气囊，甚至旋转下落的种子。枫树等旋转种子利用阻力使下落更慢，让风有更多时间把它们带离母树。
11. Common Mistakes and Safety | 常见错误与安全
Common mistakes: changing more than one variable, using different drop heights, measuring time from the wrong point, and not repeating trials. Also, some students attach strings of unequal length, which makes the canopy tilt and lose air.
常见错误：改变多个变量、使用不同下落高度、计时起点错误、不重复实验。此外，有些学生系了长度不等的绳子，使伞面倾斜并漏气。
Safety: stand on a stable platform, keep fingers clear of strings, do not drop heavy masses from high places near people, and ensure the landing area is clear. Always follow school rules for practical work.
安全：站在稳定的平台上，手指远离绳子，不要在高处向人群附近抛下重物，确保着陆区无障碍。进行实验时必须遵守学校的安全规则。
If you use scissors, cut away from your body. If you stand on a chair or ladder, ask a partner to steady it. Do not run in the laboratory to catch a falling parachute.
使用剪刀时要朝远离身体的方向剪。如果站在椅子或梯子上，请同伴扶稳。不要为了接住下落的降落伞而在实验室里奔跑。
12. Extension Ideas | 拓展思路
Investigate how string length, payload mass, canopy material, or canopy shape affects fall time. Find the terminal velocity by measuring speed over the last metre. Use a data logger with a motion sensor to record velocity-time graphs. Compare a parachute with a streamer or different number of strings.
拓展：探究绳长、载荷质量、伞面材料或伞面形状如何影响下落时间。通过测量最后一米的速度求出终端速度。使用带运动传感器的数据记录仪记录速度-时间图像。比较降落伞与飘带或不同绳数的效果。
You can also change the canopy shape from a square to a circle or hexagon while keeping the area constant. This tests whether shape alone affects drag and stability during descent.
你还可以在保持面积不变的情况下把伞面从正方形改成圆形或六边形。这样可以检验形状本身是否影响下降过程中的阻力和稳定性。
Another extension is to calculate the average speed using the equation:
另一个拓展是利用以下公式计算平均速度：
speed = distance ÷ time
Measure the exact drop distance in metres and the average fall time in seconds. Then compare average speeds for different canopy sizes and discuss why a larger canopy gives a smaller speed.
以米为单位测量准确下落距离，以秒为单位测量平均下落时间。然后比较不同伞面尺寸的平均速度，讨论为什么更大的伞面产生更小的速度。
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