📚 Cambridge AS Physics: Core Concepts Review | 剑桥AS物理核心知识点梳理
Welcome to the ultimate revision guide for Year 12 Cambridge AS Physics. This article distils the most essential concepts from the Cambridge International AS Level Physics syllabus (9702), providing clear explanations and bilingual support to help you consolidate your knowledge and prepare confidently for your exams.
欢迎阅读Year 12剑桥AS物理终极复习指南。本文提炼了剑桥国际AS物理（9702）大纲中最核心的概念，通过清晰的解释和中英双语支持，帮助你巩固知识，自信应对考试。
1. Physical Quantities and Units | 物理量与单位
All physical quantities can be expressed in terms of base quantities. The SI base units are mass (kg), length (m), time (s), electric current (A), temperature (K), amount of substance (mol), and luminous intensity (cd).
所有物理量都可以用基本量表示。国际单位制基本单位是质量（千克）、长度（米）、时间（秒）、电流（安培）、温度（开尔文）、物质的量（摩尔）和发光强度（坎德拉）。
Derived units are combinations of base units, such as the newton (N = kg m s⁻²) and the joule (J = kg m² s⁻²). Homogeneity of physical equations means that each term must have the same base units.
导出单位是基本单位的组合，例如牛顿（N = kg m s⁻²）和焦耳（J = kg m² s⁻²）。物理方程的同质性意味着每一项都必须具有相同的基本单位。
Scalars have magnitude only, while vectors have both magnitude and direction. Examples of scalars include mass, energy, and speed; examples of vectors include displacement, velocity, and force.
标量只有大小，矢量既有大小又有方向。标量的例子包括质量、能量和速率；矢量的例子包括位移、速度和力。
2. Kinematics | 运动学
Kinematics describes motion without considering its causes. Displacement, velocity, and acceleration are vector quantities; distance and speed are scalars.
运动学描述运动而不考虑其原因。位移、速度和加速度是矢量；距离和速率是标量。
For uniform acceleration, the equations of motion (SUVAT) apply:
v = u + at
s = ut + ½at²
v² = u² + 2as
s = ½(u + v)t
These equations relate initial velocity u, final velocity v, acceleration a, displacement s, and time t. They are valid only when acceleration is constant.
这些方程关联初速度u、末速度v、加速度a、位移s和时间t。它们仅在加速度恒定时成立。
Free fall under gravity has a constant acceleration g = 9.81 m s⁻² (downwards). Projectile motion can be analysed by resolving velocity into horizontal and vertical components; the horizontal component remains constant while the vertical component changes due to gravity.
重力下的自由落体具有恒定的加速度g = 9.81 m s⁻²（向下）。抛体运动可通过将速度分解为水平和竖直分量来分析；水平分量保持不变，竖直分量因重力而变化。
3. Dynamics | 动力学
Newton’s laws of motion form the foundation of dynamics. The first law states that an object remains at rest or in uniform motion unless acted upon by a resultant force.
牛顿运动定律构成了动力学的基础。第一定律指出，除非受到合外力作用，物体将保持静止或匀速直线运动。
The second law relates force, mass, and acceleration: F = ma. The newton is defined as the force that gives a 1 kg mass an acceleration of 1 m s⁻².
第二定律将力、质量和加速度联系起来：F = ma。牛顿被定义为使1千克质量产生1 m s⁻²加速度的力。
The third law states that if body A exerts a force on body B, then body B exerts an equal and opposite force on body A. These forces act on different bodies.
第三定律指出，如果物体A对物体B施加一个力，那么物体B会对物体A施加一个大小相等、方向相反的力。这些力作用在不同物体上。
Linear momentum p = mv. The principle of conservation of momentum states that the total momentum of a closed system remains constant provided no external forces act.
线动量p = mv。动量守恒原理指出，只要没有外力作用，封闭系统的总动量保持不变。
Impulse is the product of force and time (FΔt) and equals the change in momentum. Force–time graphs can be used to calculate impulse as the area under the curve.
冲量是力与时间的乘积（FΔt），等于动量的变化。力-时间图可用于计算冲量，即曲线下的面积。
4. Forces, Density and Pressure | 力、密度与压强
Density ρ = mass / volume. Pressure p = force / area (for a force acting normal to a surface). The unit of pressure is the pascal (Pa = N m⁻²).
密度ρ = 质量/体积。压强p = 力/面积（对于垂直作用于表面的力）。压强单位是帕斯卡（Pa = N m⁻²）。
In a fluid at rest, pressure increases with depth: p = hρg, where h is depth and g is gravitational field strength. The upthrust on an object submerged in a fluid equals the weight of fluid displaced (Archimedes’ principle).
在静止流体中，压强随深度增加：p = hρg，其中h是深度，g是重力场强度。浸没在流体中的物体受到的浮力等于被排开流体的重量（阿基米德原理）。
The moment of a force about a point is force × perpendicular distance from the point. For an object in equilibrium, the sum of clockwise moments equals the sum of anticlockwise moments about any point.
力对某点的力矩等于力乘以从该点到力作用线的垂直距离。对于平衡的物体，关于任意点的顺时针力矩之和等于逆时针力矩之和。
Centre of gravity is the point where the entire weight of an object appears to act. A system is in equilibrium if the resultant force is zero and the resultant moment is zero.
重心是物体全部重量看似作用的点。如果合力为零且合力矩为零，则系统处于平衡状态。
5. Work, Energy and Power | 功、能与功率
Work done by a constant force is W = Fs cosθ, where θ is the angle between the force and displacement. Energy is the capacity to do work; both are measured in joules (J).
恒力做的功为W = Fs cosθ，其中θ是力与位移之间的夹角。能量是做功的能力；两者均以焦耳（J）为单位。
Kinetic energy Ek = ½mv² and gravitational potential energy Ep = mgh. The principle of conservation of energy states that energy cannot be created or destroyed, only transferred or transformed.
动能Ek = ½mv²，重力势能Ep = mgh。能量守恒原理指出，能量不能被创造或毁灭，只能转移或转换。
Power is the rate of doing work: P = W/t. An alternative expression for power is P = Fv, where F is the force and v is the velocity in the direction of the force. Efficiency = useful output power / input power × 100%.
功率是做功的速率：P = W/t。功率的另一种表达式是P = Fv，其中F是力，v是沿力方向的速度。效率 = 有用输出功率/输入功率 × 100%。
6. Deformation of Solids | 固体形变
Hooke’s law states that the extension of a spring is proportional to the applied force, provided the elastic limit is not exceeded: F = kx, where k is the spring constant.
胡克定律指出，只要不超过弹性极限，弹簧的伸长量与施加的力成正比：F = kx，其中k是弹簧常数。
Elastic deformation is reversible; plastic deformation is permanent. The elastic limit is the point beyond which the material no longer returns to its original shape.
弹性形变是可逆的；塑性形变是永久的。弹性极限是材料不再恢复原状的临界点。
Stress σ = force / cross-sectional area; strain ε = extension / original length. Young modulus E = stress / strain for a material under tensile stress within the limit of proportionality.
应力σ = 力/横截面积；应变ε = 伸长量/原始长度。杨氏模量E = 应力/应变，适用于在比例极限内受拉伸的材料。
The area under a force–extension graph gives the work done (elastic potential energy) stored in the material: E = ½Fx = ½kx² for a Hookean spring.
力-伸长量图下的面积表示储存在材料中的功（弹性势能）：对于遵循胡克定律的弹簧，E = ½Fx = ½kx²。
7. Waves | 波
Progressive waves transfer energy without transferring matter. In transverse waves, oscillations are perpendicular to the direction of energy transfer; in longitudinal waves, oscillations are parallel.
行波传递能量而不传递物质。在横波中，振动方向与能量传递方向垂直；在纵波中，振动方向与能量传递方向平行。
Key wave quantities: displacement, amplitude, wavelength λ, frequency f, period T. The wave speed v = fλ = λ/T. Phase difference can be measured in degrees or radians.
关键波动量：位移、振幅、波长λ、频率f、周期T。波速v = fλ = λ/T。相位差可以用度或弧度衡量。
Intensity I ∝ (amplitude)² and inversely proportional to the square of the distance from a point source (in
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