📚 Mastering Key Concepts in PH01 International AS Physics (May 2023) | PH01国际AS物理（2023年5月）核心概念解析
The PH01 International AS Physics examination (paper code PH01/INS, 9 May 2023) covers the cornerstone topics of mechanics, materials and fluid behaviour. This revision guide explains each key concept with parallel English and Chinese explanations, aligned to the Edexcel IAL specification. Every section pairs the physics theory you must know with the exam skills you must show, so that after working through it you can confidently tackle multiple-choice, short-answer and longer structured questions.
PH01国际AS物理考试（试卷代码PH01/INS，2023年5月9日）涵盖力学、材料与流体行为的基础课题。本复习指南以中英文对照讲解每个核心概念，贴合爱德思IAL大纲。每一节都把必须掌握的物理理论与必须体现的应试技能配对讲解，读完之后，你将能自信应对选择题、简答题和结构化长题。
1. Exam Overview and Specification Map | 考试概览与大纲范围
PH01 is the first unit of the Edexcel International Advanced Level Physics course, usually taken in the first year of study. The paper is 1 hour 30 minutes long and is marked out of 80, contributing 20 percent of the full IAL Physics qualification. The question paper is divided into three styles of question: multiple-choice, short-answer calculations and extended structured questions worth four to six marks each.
PH01是爱德思国际A Level物理课程的第一单元，通常在AS阶段第一年参加考试。考试时长1小时30分钟，满分80分，占整个IAL物理资格总分的20%。试卷由三类题型组成：选择题、短答计算题，以及每题4至6分的结构化长题。
The May 2023 specification content clusters around three strands: mechanics (kinematics, dynamics, momentum, energy and power), materials (density, Hooke's law, stress, strain and the Young modulus) and fluid behaviour (pressure, upthrust, viscosity, Stokes' law and terminal velocity). Because these strands share the same mathematical toolkit, an error in one topic often propagates into another, so revision should always connect the topics rather than treat them as separate boxes.
2023年5月的大纲内容围绕三条主线：力学（运动学、动力学、动量、能量与功率）、材料（密度、胡克定律、应力、应变与杨氏模量）以及流体行为（压强、浮力、黏度、斯托克斯定律与终端速度）。由于这三条主线共用同一套数学工具，一个课题的错误常常会蔓延到另一个课题，因此复习时应当把各主题串联起来，而不是把它们当作互不相干的独立板块。
- Mechanics | 力学: motion, forces, momentum, work-energy-power | 运动、力、动量、功—能—功率
- Materials | 材料: density, deformation, stress-strain | 密度、形变、应力—应变
- Fluids | 流体: pressure, upthrust, viscosity, terminal velocity | 压强、浮力、黏度、终端速度
2. Kinematics and Motion Graphs | 运动学与运动图像
Kinematics deals with the description of motion without considering its causes. Displacement s, velocity v and acceleration a are vector quantities; distance and speed are their scalar counterparts. For motion with uniform (constant) acceleration, four equations of motion - often called the SUVAT equations - apply, where each letter stands for s, u, v, a and t.
运动学描述运动的规律而不探究其原因。位移s、速度v和加速度a是矢量；路程和速率则是对应的标量。对于匀加速（加速度恒定）运动，可使用四个运动方程——常称为SUVAT方程，五个字母分别代表s、u、v、a、t。
v = u + a t
s = u t + ½ a t²
v² = u² + 2 a s
s = ½ (u + v) t
Here u is the initial velocity, v the final velocity, a the constant acceleration, t the time taken and s the displacement. The equations are only valid when the acceleration is constant, so they must never be used for a falling object that has reached terminal velocity, nor for any motion where the acceleration varies.
其中u为初速度，v为末速度，a为恒定加速度，t为所用时间，s为位移。这些方程仅在加速度恒定时成立，因此绝不能用于已达到终端速度的下落物体，也不能用于加速度发生变化的运动。
Motion graphs provide powerful visual tools. On a displacement-time (s-t) graph, the gradient equals velocity: a straight line indicates constant velocity, while a curve indicates changing velocity. On a velocity-time (v-t) graph, the gradient is acceleration, and the area under the graph gives displacement. On an acceleration-time (a-t) graph, the area gives the change in velocity. Note that a negative gradient on a v-t graph means deceleration only if the object is still moving in the positive direction.
运动图像提供了有力的视觉工具。在位移-时间(s-t)图上，斜率等于速度：直线表示匀速，曲线表示变速。在速度-时间(v-t)图上，斜率为加速度，图线下的面积表示位移。在加速度-时间(a-t)图上的面积则表示速度变化量。注意，v-t图上的负斜率只有在物体仍沿正方向运动时才代表减速。
Typical exam tasks ask you to sketch the v-t graph for a bouncing ball, to read off a gradient using a tangent, or to find a displacement by splitting the area into triangles and trapeziums. Always quote the units of a gradient (for example m s⁻²) and of an area (for example m) in your answer.
典型考题要求你画出弹跳小球的v-t图、用切线读出某点斜率，或通过把面积拆分为三角形与梯形来求位移。答题时务必写出斜率的单位（如m s⁻²）与面积的单位（如m）。
3. Projectile Motion | 抛体运动
Projectile motion is analysed by resolving the initial velocity into independent horizontal and vertical components. If a projectile is launched at speed u at an angle θ to the horizontal, then the horizontal component is u cos θ and the vertical component is u sin θ. The two directions are then treated completely separately.
抛体运动通过把初速度分解为彼此独立的水平分量与竖直分量来分析。若抛体以速率u、与水平方向成θ角抛出，则水平分量为u cos θ，竖直分量为u sin θ。随后两个方向被完全分开处理。
orizontal displacement is simply x = u cos θ × t. Vertically, the only force is weight, giving a constant downward acceleration g = 9.81 m s⁻², so the vertical velocity and displacement follow the SUVAT equations with a = −g if upward is taken as positive.
水平方向上，若空气阻力可忽略，则没有力、因而没有加速度，水平速度保持不变，水平位移即 x = u cos θ × t。竖直方向上唯一的力是重力，产生恒定的向下加速度 g = 9.81 m s⁻²；若取向上为正，则竖直速度与竖直位移遵循取 a = −g 的SUVAT方程。
x = (u cos θ) t
y = (u sin θ) t − ½ g t²
vy = u sin θ − g t
is t = 2 u sin θ ÷ g, the maximum height is H = u² sin²θ ÷ (2g), and the horizontal range is R = u² sin 2θ ÷ g. The range is greatest when θ = 45°.
由这些关系式可推出抛体从同一水平高度抛出并落回该高度时的三个标准结论：飞行时间 t = 2 u sin θ ÷ g，最大高度 H = u² sin²θ ÷ (2g)，水平射程 R = u² sin 2θ ÷ g。当 θ = 45° 时射程最大。
At the highest point of the trajectory the vertical velocity is momentarily zero, but the horizontal velocity still has its full value, so the speed at the top is not zero. If air resistance is not negligible, the trajectory becomes asymmetric, the range is reduced and the descent is steeper than the ascent.
在轨迹最高点，竖直速度瞬时为零，但水平速度仍保持其全部数值，所以最高点的速率并不为零。若空气阻力不可忽略，轨迹将不再对称，射程减小，且下降段比上升段更陡。
4. Forces, Newton's Laws and Equilibrium | 力、牛顿定律与平衡
Newton' ins at rest or moves with constant velocity unless acted upon by a resultant force. Newton' equals the rate of change of momentum, which for constant mass reduces to F = m a. Newton' exerts a force on body B, then B exerts an equal and opposite force of the same type on A.
牛顿第一定律指出：物体除非受到合外力作用，否则保持静止或匀速直线运动。牛顿第二定律指出：合外力等于动量的变化率，当质量恒定时简化为 F = m a。牛顿第三定律指出：若物体A对物体B施加一个力，则B对A施加一个大小相等、方向相反、性质相同的力。
F = m a
W = m g
F ≤ μ R
In the friction relationship, R is the normal contact force and μ is the coefficient of friction; the inequality shows that the frictional force equals μR only at the point of limiting equilibrium, when sliding is about to begin. A frequent exam error is to treat the normal contact force as always equal to the weight, which is false on an inclined plane or in a lift that is accelerating.
在摩擦关系中，R为法向接触力，μ为摩擦系数；不等号表明只有处于极限平衡（即将开始滑动）时，摩擦力才等于 μR。常见错误是把法向接触力一律当作重力，这在一斜面上或正在加速的电梯中都是不成立的。
pendicular to the slope, m g cos θ. The normal contact force is then R = m g cos θ, and the component driving motion down the slope is m g sin θ minus any friction.
在与水平方向成θ角的斜面问题上，应把重力分解为沿斜面向下的分量 m g sin θ 与垂直于斜面的分量 m g cos θ。此时法向接触力 R = m g cos θ，而使物体沿斜面向下滑动的分量则是 m g sin θ 减去摩擦力。
Equilibrium means the resultant force is zero, which requires both the vector sum of the forces and, when the forces are resolved, the sum in each perpendicular direction to be zero. Always draw a free-body diagram first, label every force with its type and direction, and mark the direction in which you are resolving.
平衡意味着合外力为零，这既要求各力的矢量和为零，也要求在分解后每一对互相垂直方向上的分力之和均为零。做题时先画受力分析图，标注每个力的性质与方向，并标明你所选定的分解方向。
5. Momentum and Collisions | 动量与碰撞
t is a vector quantity measured in kg m s⁻¹. The impulse of a force is the product of the force and the time for which it acts, F Δt, and the impulse-momentum theorem states that the impulse equals the change in momentum.
线动量定义为质量与速度的乘积，p = m v，是矢量，单位为 kg m s⁻¹。力的冲量是力与其作用时间的乘积 F Δt；冲量—动量定理指出，冲量等于动量的变化量。
p = m v
F Δt = Δp = m v − m u
The principle of conservation of momentum states that the total momentum of a system remains constant provided no external resultant force acts on the system. This makes it the key tool for analysing collisions and explosions. Remember that momentum has direction, so velocities in opposite directions must be given opposite signs before you add them.
动量守恒原理指出：只要系统不受合外力，系统总动量保持不变。这使它成为分析碰撞与爆炸的关键工具。切记动量有方向，因此方向相反的各个速度在相加之前必须先赋予相反的符号。
In a perfectly elastic collision both momentum and kinetic energy are conserved. In an inelastic collision momentum is still conserved, but some kinetic energy is transferred to thermal energy, sound or deformation, so kinetic energy decreases. In an explosion the total momentum before is zero, so the total momentum after must also be zero, and kinetic energy increases because chemical or elastic energy is released.
在完全弹性碰撞中，动量与动能同时守恒。在非弹性碰撞中，动量仍然守恒，但一部分动能转化为内能、声能或形变能，因此动能减小。在爆炸情形中，爆发前的总动量为零，所以爆发后的总动量也必须为零，而动能增加，因为有化学能或弹性势能被释放出来。
Real-world applications are exam favourites: crumple zones, airbags, seat belts, bicycle helmets and crash barriers all work by extending the collision time. Since the change in momentum is fixed by the collision, increasing Δt reduces the average force F experienced by the occupants.
现实应用是高频考点：溃缩吸能区、安全气囊、安全带、自行车头盔和防撞护栏，都是通过延长碰撞时间来起作用。由于碰撞过程中动量的变化量是确定的，增大 Δt 就能减小乘员所受的平均力 F。
6. Work, Energy and Power | 功、能量与功率
on: W = F s cos θ, measured in joules. If the force is perpendicular to the displacement, no work is done by that force.
当力使其作用点沿力的方向发生位移时，就做了功；其大小由力在运动方向上的分量决定：W = F s cos θ，单位为焦耳。若力与位移垂直，则该力不做功。
W = F s cos θ
Ek = ½ m v²
ΔEp = m g Δh
a mass through a height, ΔEₚ = m g Δh. The principle of conservation of energy states that energy cannot be created or destroyed but only transferred or transformed, so in a closed system the total energy remains constant.
动能是物体因运动而具有的能量，Eₖ = ½ m v²；重力势能是把质量提升一段高度所储存的能量，ΔEₚ = m g Δh。能量守恒原理指出，能量既不能创生也不能消灭，只能转移或转化，因此在孤立系统中总能量保持不变。
v, power can also be written as P = F v. Efficiency is the useful output energy or power divided by the total input energy or power, usually expressed as a percentage.
功率是做功的速率或能量转移的速率，P = W ÷ t，单位为瓦特。当恒力F使物体以恒定速度v运动时，功率也可写作 P = F v。效率等于有用输出能量（或功率）除以总输入能量（或功率），通常用百分比表示。
Typical calculations combine several ideas: find the work done against friction on a slope, then the gain in gravitational potential energy, then the average power over the journey. Always check whether energy is lost to resistive forces before you equate initial and final mechanical energy.
典型计算题会综合多个知识点：先求沿斜面克服摩擦力所做的功，再求重力势能的增加量，最后求整段行程的平均功率。在把初末机械能直接相等之前，务必确认是否有能量损失于阻力做功。
7. Materials: Stress, Strain and the Young Modulus | 材料：应力、应变与杨氏模量
to the applied force provided the limit of proportionality is not exceeded; this is Hooke's law, F = k x, where k is the stiffness constant in N m⁻¹.
密度定义为单位体积的质量，ρ = m ÷ V，单位为 kg m⁻³。材料被拉伸时，只要不超过比例极限，伸长量就与所施加的力成正比，这就是胡克定律 F = k x，其中k为劲度系数，单位为 N m⁻¹。
σ = F ÷ A
ε = x ÷ L
E = σ ÷ ε = (F L) ÷ (A x)
Tensile stress σ is the force per unit cross-sectional area, measured in pascals; tensile strain ε is the fractional change in length and has no unit. The Young modulus E is the ratio of stress to strain and is therefore also measured in pascals. Because stress and strain are independent of the size of the specimen, the Young modulus is a genuine property of the material itself.
拉应力σ是单位横截面积上的力，单位为帕斯卡；拉应变ε是长度的相对变化量，没有单位。杨氏模量E是应力与应变之比，因此单位同样是帕斯卡。由于应力与应变都与试样的尺寸无关，杨氏模量是材料本身的真实属性。
, the area gives the energy stored per unit volume, and the gradient in the linear region equals the Young modulus.
力—伸长量图线下的面积表示弹性储存的能量，在线性区域内为 E = ½ F x = ½ k x²。在应力—应变图上，面积表示单位体积储存的能量，而线性区域的斜率等于杨氏模量。
You must be able to describe the shape of a stress-strain curve: the linear region up to the limit of proportionality, the elastic limit beyond which permanent deformation occurs, the yield point where the material suddenly extends, the plastic region, and finally the breaking point showing the ultimate tensile strength. A stiff material has a steep gradient; a strong material has a high breaking stress; a brittle material breaks with little plastic deformation, while a ductile material shows considerable plastic flow.
你必须能够描述应力—应变曲线的形状：从原点到比例极限的线性区；超过弹性极限后出现永久形变；屈服点处材料突然伸长；随后是塑性区；最后是断裂点，对应极限抗拉强度。刚度大的材料斜率陡；强度高的材料断裂应力大；脆性材料几乎不发生塑性形变就断裂，而韧性材料则表现出明显的塑性流动。
8. Fluid Behaviour: Pressure, Density and Upthrust | 流体行为：压强、密度与浮力
below the surface is given by p = ρ g h, where ρ is the density of the fluid and g is the gravitational field strength. This relationship explains why the pressure on a dam wall increases with depth and why the wall must be thicker at the base.
压强定义为单位面积上的法向力，p = F ÷ A，单位为帕斯卡，1 Pa = 1 N m⁻²。在静止流体中，液面以下深度h处的压强由 p = ρ g h 给出，其中ρ为流体密度，g为重力场强度。这一关系解释了为什么坝体所受压强随深度增加，以及为什么坝底必须更厚。
p = F ÷ A
p = ρ g h
Upthrust = ρfluid g Vdisplaced
Archimedes' principle states that a body wholly or partly immersed in a fluid experiences an upthrust equal to the weight of the fluid it displaces. Because this upthrust acts upwards while weight acts downwards, the resultant force determines whether the body sinks, floats or remains in equilibrium.
阿基米德原理指出：完全或部分浸入流体中的物体所受的浮力，等于它排开的那部分流体的重力。由于浮力向上、重力向下，二者的合力决定了物体下沉、漂浮还是处于平衡。
Floating occurs when the upthrust equals the weight, which means the weight of the displaced fluid equals the whole weight of the floating body. This is why a ship made of steel can float: its overall density, counting the air inside the hull, is less than that of water. A submerged body rises if its average density is less than the fluid density, sinks if it is greater, and stays in equilibrium if the two are equal.
当浮力等于重力时物体漂浮，即被排开流体的重力等于漂浮物体的全部重力。这就是钢制轮船能浮起来的原因：把船体内的空气计算在内，它的平均密度小于水。浸没的物体，若其平均密度小于流体密度则上浮，大于则下沉，相等则处于平衡。
plus ρ g h. Exam questions often combine p = ρ g h with p = F ÷ A to find the force on a submerged surface, so keep the two equations clearly separated in your working.
注意液体中的压强向各个方向传递，而在与大气相通的液体中，某点的总压强等于大气压加上 ρ g h。考题常把 p = ρ g h 与 p = F ÷ A 结合起来求浸没表面所受的力，因此在解题过程中要把两个公式清楚地分开使用。
9. Viscosity, Stokes' Law and Terminal Velocity | 黏度、斯托克斯定律与终端速度
Viscosity is a measure of a fluid's resistance to flow, arising from internal friction between layers of fluid moving at different speeds. A more viscous fluid produces a larger drag force on an object moving through it, and viscosity decreases as temperature rises for most liquids.
黏度是流体抵抗流动能力的量度，源于流体中速度不同的各层之间的内摩擦。黏度越大的流体，对穿过它的物体产生的阻力越大；对大多数液体而言，黏度随温度升高而减小。
here moving slowly through a fluid in streamline flow, the viscous drag is given by Stokes' law, F = 6 π η r v, where η
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