📚 Experimental Determination of Velocity and Acceleration | 实验测定速度与加速度
Measuring the velocity and acceleration of moving objects is one of the most fundamental practical skills in A-Level Physics. In the CIE syllabus, students must understand how to use ticker tape timers, light gates, and motion sensors, and how to analyse the data they produce with appropriate equations and graphical methods.
测量运动物体的速度与加速度是A-Level物理中最基本的实验技能之一。在CIE考纲中，学生必须掌握如何使用打点计时器、光电门和运动传感器，并学会用相应的公式和图解法分析所获得的实验数据。
1. Core Principles of Motion Measurement | 运动测量的核心原理
All motion measurements reduce to two basic quantities: displacement and time. Velocity is displacement per unit time, and acceleration is the rate of change of velocity. Therefore, every experimental method in this topic is a way of measuring distances and time intervals as accurately as possible.
一切运动测量归根结底都归结为两个基本物理量：位移和时间。速度是单位时间内的位移，加速度是速度的变化率。因此，本主题中的每一种实验方法都是尽可能精确地测量距离和时间间隔的方式。
When choosing equipment, we consider resolution, timing accuracy, and whether the measurement disturbs the motion being studied. For instance, optical methods do not touch the object and therefore introduce no friction, while mechanical methods such as ticker tape do add a small resistive drag.
选择仪器时，我们需要考虑分辨度、计时精度以及测量是否干扰被研究的运动。例如，光学方法不接触物体，因此不会引入摩擦力；而打点计时器这类机械方法则会附加微小的阻力。
2. The Ticker Tape Timer | 打点计时器
records the motion. The time interval between two adjacent dots is exactly 1/50 = 0.02 s.
打点计时器是一种每秒在纸带上打出50个点的电子设备。当纸带被运动的小车拖过计时器时，相邻点之间的距离便记录了物体的运动情况。相邻两点之间的时间间隔恰好为1/50 = 0.02 s。
If the dots are equally spaced, the tape is moving at constant velocity. If the spacing increases, the tape is speeding up
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