📚 Year 9 OCR Physics: Formula & Theorem Quick Reference Handbook | 九年级 OCR 物理：公式定理速查手册
This quick reference handbook compiles the essential formulas and theorems for Year 9 OCR Physics. Each section presents a key formula, explains its components, and highlights important units. Use this guide to reinforce your understanding and prepare for assessments with confidence.
本速查手册汇编了九年级 OCR 物理的关键公式和定理。每节呈现一个核心公式，解释其组成部分并强调重要单位。使用本指南加深理解并从容备考。
1. Speed and Velocity | 速度与速率
where v represents speed (in metres per second, m/s), d is distance (in metres, m), and t is time (in seconds, s). Speed is a scalar quantity, which means it has magnitude but no direction.
v = d / t
物体的平均速度等于总行驶距离除以总时间。关系式写作 v = d / t，其中 v 代表速度（单位米每秒，m/s），d 为距离（米，m），t 为时间（秒，s）。速度是标量，即只有大小没有方向。
Velocity is speed in a given direction; it is therefore a vector quantity. If the direction of motion changes, the velocity changes even if the speed remains constant. For example, a car going around a roundabout at a steady 20 mph has a constantly changing velocity.
速率是具有方向的速度，因此是矢量。如果运动方向改变，即使速率不变，速度也会改变。例如，一辆车以恒定的 20 mph 绕行环形交叉路口，其速度一直在变化。
2. Acceleration | 加速度
a is acceleration (in metres per second squared, m/s²), v is final velocity (m/s), u is initial velocity (m/s), and t is time (s). Acceleration is also a vector.
a = (v − u) / t
加速度衡量物体速度变化的快慢。定义式为 a = (v − u) / t，其中 a 为加速度（米每二次方秒，m/s²），v 为末速度，u 为初速度，t 为时间。加速度也是矢量。
it is slowing down. For a car braking from 30 m/s to 10 m/s in 5 seconds, the acceleration is (10 − 30)/5 = −4 m/s².
正加速度表示物体沿选定方向加速，而负加速度（常称为减速）表示物体在减速。一辆车在 5 秒内从 30 m/s 刹车到 10 m/s，加速度为 (10 − 30)/5 = −4 m/s²。
3. Newton's Second Law | 牛顿第二定律
Newton' force (in newtons, N), m is the mass (in kilograms, kg), and a is the acceleration (m/s²). The law explains that a greater force produces a greater acceleration, and a larger mass requires a larger force to achieve the same acceleration.
F = m a
牛顿第二定律将作用在物体上的合力与其质量和加速度联系起来：F = m a。其中 F 为合力（牛顿，N），m 为质量（千克，kg），a 为加速度（m/s²）。该定律表明，力越大加速度越大，质量越大需要越大的力才能产生相同的加速度。
problems, you will balance multiple forces to find the net force before applying F = m a.
1 牛顿的定义是使 1 千克质量产生 1 m/s² 加速度所需的力。在许多问题中，需要先平衡多个力得出合力，再应用 F = m a。
4. Weight and Mass | 重量与质量
m is mass (kg), and g is the gravitational field strength. On Earth, g is approximately 9.8 N/kg but is often rounded to 10 N/kg for simplicity. Weight is a vector directed towards the centre of the planet.
W = m g
重量是物体所受的重力。计算公式为 W = m g，其中 W 为重量（N），m 为质量（kg），g 为重力场强度。地球表面 g 约等于 9.8 N/kg，通常简化为 10 N/kg。重量是指向地心的矢量。
Mass is the amount of matter in an object and remains the same everywhere. Weight, however, varies with the gravitational field strength — an astronaut has the same mass on the Moon but weighs only about one sixth as much because the Moon's g is about 1.6 N/kg.
质量是物体所含物质的多少，在任何地方都一样。而重量随引力场强变化——宇航员在月球上质量不变，但重量只有地球的约六分之一，因为月球 g 约为 1.6 N/kg。
5. Pressure | 压强
/ A, where P is pressure (pascals, Pa, equivalent to N/m²), F is the normal force (N), and A is the area over which the force acts (m²). A concentrated force over a small area creates high pressure.
P = F / A
压强是作用在表面单位面积上的力。公式为 P = F / A，其中 P 为压强（帕斯卡，Pa，等于 N/m²），F 为垂直力（N），A 为受力面积（m²）。力集中作用在小面积上会形成高压强。
Everyday applications rely on changing area to alter pressure. A sharp knife has a very small edge area, producing high pressure to cut easily. Snowshoes use a large area to reduce pressure, preventing the wearer from sinking into the snow.
Published by TutorHao | Year 9 Physics Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图