Forces and Motion: Key Exam Points for IB & WJEC Science | 力与运动：IB/WJEC科学考点精讲

📚 Forces and Motion: Key Exam Points for IB & WJEC Science | 力与运动：IB/WJEC科学考点精讲

Force and motion form the cornerstone of mechanics in both IB Physics and WJEC Science specifications. Understanding these concepts is vital for tackling exam questions, from interpreting graphs to applying Newton’s laws. This article distills key exam points, common pitfalls, and essential equations. Let’s dive in.

力与运动是IB物理和WJEC科学课程中力学的基石。理解这些概念对于解答从图像分析到牛顿定律应用的考试题目至关重要。本文提炼了核心考点、常见错误和必备公式，让我们开始吧。

1. Scalar and Vector Quantities | 标量和矢量

Scalars are quantities that have magnitude only. Examples include distance, speed, mass, energy, and time. Vectors have both magnitude and direction. Examples are displacement, velocity, acceleration, force, and momentum. In exams, always distinguish between distance (scalar) and displacement (vector). When adding vectors, use the tip-to-tail method or resolve into components. For perpendicular vectors, use Pythagoras’ theorem to find the resultant magnitude and trigonometry for direction.

标量是只有大小的量，如距离、速率、质量、能量和时间。矢量既有大小又有方向，如位移、速度、加速度、力和动量。考试中务必区分距离（标量）与位移（矢量）。矢量相加可采用三角形法则（首尾相接法）或正交分解。对于相互垂直的矢量，用勾股定理求合矢量的大小，用三角函数求方向。

Remember that the direction of a vector can be described by an angle relative to a reference line, e.g., 30° above the horizontal.

记住矢量的方向可用与参考线的夹角表示，例如与水平线成30°。

2. Speed, Velocity and Acceleration | 速度、速率和加速度

Speed is the rate of change of distance: average speed = total distance / time. Velocity is the rate of change of displacement: v = Δs / Δt. Acceleration is the rate of change of velocity: a = Δv / Δt. In IB and WJEC questions, you may be asked to calculate average acceleration from a velocity-time graph. Uniform acceleration means constant acceleration, such as free fall near Earth’s surface (g ≈ 9.8 m s⁻²). Note that deceleration is negative acceleration.

速率是距离的变化率：平均速率 = 总距离 / 时间。速度是位移的变化率：v = Δs / Δt。加速度是速度的变化率：a = Δv / Δt。在IB和WJEC题目中，常需根据速度-时间图像计算平均加速度。匀加速指加速度不变，如近地表面的自由落体（g ≈ 9.8 m s⁻²）。注意减速是负加速度。

Make sure to use SI units: metres (m), seconds (s), metres per second (m s⁻¹), and metres per second squared (m s⁻²).

务必使用国际单位：米（m）、秒（s）、米每秒（m s⁻¹）和米每二次方秒（m s⁻²）。Published by TutorHao | IB Science Revision Series | aleveler.com

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