📚 AS Physics Unit 1 Revision: Mechanics, Materials and Motion | AS 物理第一单元复习：力学、材料与运动
This revision guide covers the core content of AS Physics Unit 1. It brings together key definitions, equations, graph interpretations and exam skills for mechanics and materials. Use the paired English and Chinese explanations to check your understanding as you work through each section.
本复习指南涵盖 AS 物理第一单元的核心内容。它汇集了力学和材料部分的关键定义、公式、图像解读和考试技巧。请在学习每一节时，对照中英文解释检查自己的理解。
1. SI Units, Prefixes and Scalar/Vector Basics | 国际单位制、词头与标量/矢量基础
All physical quantities are measured using SI base units: metre for length, kilogram for mass, second for time, ampere for current, kelvin for temperature, mole for amount of substance, and candela for luminous intensity. Derived units such as the newton are expressed as kg m s⁻².
所有物理量都使用国际单位制基本单位进行测量：长度用米，质量用千克，时间用秒，电流用安培，温度用开尔文，物质的量用摩尔，发光强度用坎德拉。导出单位如牛顿表示为 kg m s⁻²。
Prefixes are used to express very large or very small values. Common examples include kilo (10³), mega (10⁶), giga (10⁹), milli (10⁻³), micro (10⁻⁶) and nano (10⁻⁹). You must be able to convert between prefixes quickly in calculations.
词头用于表示非常大或非常小的数值。常见例子包括千（10³）、兆（10⁶）、吉（10⁹）、毫（10⁻³）、微（10⁻⁶）和纳（10⁻⁹）。你必须能够在计算中快速进行词头换算。
Scalars have magnitude only, while vectors have both magnitude and direction. Examples of scalars include distance, speed, mass, energy and temperature. Examples of vectors include displacement, velocity, acceleration, force and momentum.
标量只有大小，而矢量既有大小又有方向。标量的例子包括路程、速率、质量、能量和温度。矢量的例子包括位移、速度、加速度、力和动量。
2. Motion Graphs and Velocity-Time Interpretation | 运动图像与速度-时间图像解读
A displacement-time graph shows how position changes with time. The gradient of a displacement-time graph gives velocity. A straight line represents constant velocity, while a curved line represents changing velocity.
位移-时间图像显示位置随时间的变化。位移-时间图像的斜率表示速度。直线表示速度恒定，而曲线表示速度在变化。
A velocity-time graph is one of the most powerful tools in Unit 1. The gradient gives acceleration, and the area between the line and the time axis gives displacement. You should be able to describe motion from the shape of the graph.
速度-时间图像是第一单元中最有力的工具之一。其斜率表示加速度，图线与时间轴之间的面积表示位移。你应该能够根据图像形状描述物体的运动。
- Horizontal line: constant velocity, zero acceleration
- Positive gradient: positive acceleration
- Negative gradient: negative acceleration or deceleration
- Area under graph: total displacement
- 水平线：速度恒定，加速度为零
- 正斜率：正加速度
- 负斜率：负加速度或减速
- 图线下方面积：总位移
When a graph is non-linear, use a tangent to find the instantaneous gradient. For uniform acceleration, the graph is a straight line, which makes calculations simpler.
当图像为非线性时，使用切线求瞬时斜率。对于匀加速运动，图像为直线，这使得计算更简单。
3. SUVAT Equations of Constant Acceleration | 匀加速运动的 SUVAT 方程
The SUVAT equations apply only when acceleration is constant. The five quantities are displacement s, initial velocity u, final velocity v, acceleration a and time t. You need three known values to find a fourth.
SUVAT 方程仅适用于加速度恒定的情况。五个物理量分别是位移 s、初速度 u、末速度 v、加速度 a 和时间 t。你需要三个已知量来求第四个量。
v = u + at
s = ½ (u + v) t
s = ut + ½ at²
v² = u² + 2as
Always choose the equation that contains the unknown you want and does not require the quantity you do not have. Pay attention to signs: quantities in opposite directions must have opposite signs.
始终选择包含你要求解的未知量且不需要你未给出的量的方程。注意符号：方向相反的物理量必须使用相反的符号。
For an object thrown vertically upward, take upward as positive. Then acceleration due to gravity is negative, a = -9.81 m s⁻². At the highest point, the final velocity is momentarily zero.
对于竖直上抛的物体，取向上为正方向。此时重力加速度为负值，a = -9.81 m s⁻²。在最高点，末速度瞬时为零。
4. Newton’s Laws, Momentum and Impulse | 牛顿定律、动量与冲量
Newton’s first law states that an object remains at rest or in uniform motion unless acted on by a resultant force. Inertia is the tendency of an object to resist changes in its motion.
牛顿第一定律指出，除非受到合外力作用，物体将保持静止或匀速直线运动状态。惯性是物体抵抗其运动状态变化的趋势。
Newton’s second law states that the resultant force on an object is equal to the rate of change of its momentum. For constant mass, this simplifies to F = ma, where force is in newtons, mass in kilograms and acceleration in metres per second squared.
牛顿第二定律指出，作用在物体上的合外力等于其动量的变化率。对于质量恒定的情况，该定律简化为 F = ma，其中力的单位为牛顿，质量单位为千克，加速度单位为米每二次方秒。
Newton’s third law states that if object A exerts a force on object B, then object B exerts an equal and opposite force on object A. These forces act on different objects and never cancel each other.
牛顿第三定律指出，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。这两个力作用在不同物体上，永远不能相互抵消。
Momentum is defined as p = mv. Impulse is the change in momentum and equals force multiplied by time, Δp = FΔt. The area under a force-time graph gives impulse or change in momentum.
动量定义为 p = mv。冲量是动量的变化量，等于力乘以时间，Δp = FΔt。力-时间图像下方的面积表示冲量或动量变化。
5. Moments, Centre of Gravity and Equilibrium | 力矩、重心与平衡
A moment is the turning effect of a force about a pivot. It is calculated as the product of force and perpendicular distance from the pivot: moment = F × d. The unit is the newton metre, N m.
力矩是力绕支点产生的转动效应。它等于力与从支点到力作用线垂直距离的乘积：力矩 = F × d。单位是牛顿米，N m。
The principle of moments states that for an object in rotational equilibrium, the sum of clockwise moments about any pivot equals the sum of anticlockwise moments. This is essential for solving beam and bridge problems.
力矩原理指出，对于处于转动平衡的物体，绕任一支点的顺时针力矩之和等于逆时针力矩之和。这是解决横梁和桥梁问题的基础。
The centre of gravity of an object is the point where the entire weight appears to act. For a uniform regular object, it lies at the geometric centre. If a suspended object is in equilibrium, the centre of gravity lies directly below the point of suspension.
物体的重心是全部重力似乎作用的点。对于均匀的规则物体，重心位于几何中心。如果悬挂物体处于平衡状态，重心位于悬挂点正下方。
A body is in equilibrium when the resultant force is zero and the resultant moment is zero. This gives two independent conditions: no linear acceleration and no angular acceleration.
当合外力为零且合力矩为零时，物体处于平衡状态。这给出两个独立条件：无线性加速度且无角加速度。
6. Work, Energy and Power | 功、能量与功率
Work is done when a force moves its point of application in the direction of the force. It is calculated as W = F × d, where d is the distance moved in the direction of the force. The unit is the joule, J.
当力使其作用点沿力的方向移动时，就做了功。功的计算公式为 W = F × d，其中 d 是沿力的方向移动的距离。功的单位是焦耳，J。
Kinetic energy is the energy an object has due to its motion, given by Eₖ = ½mv². Gravitational potential energy is the energy stored by an object raised in a gravitational field, given by Eₚ = mgh.
动能是物体由于运动而具有的能量，公式为 Eₖ = ½mv²。重力势能是物体在重力场中被抬高时储存的能量，公式为 Eₚ = mgh。
Power is the rate of doing work or transferring energy, P = W/t or P = E/t. The unit is the watt, W, where 1 W = 1 J s⁻¹. For a moving object, instantaneous power can also be written as P = Fv.
功率是做功或能量转移的速率，P = W/t 或 P = E/t。单位是瓦特，W，其中 1 W = 1 J s⁻¹。对于运动物体，瞬时功率也可写成 P = Fv。
The principle of conservation of energy states that energy cannot be created or destroyed, only transferred into different forms. In mechanics, useful energy transfers are compared with total input using efficiency = useful energy output / total energy input.
能量守恒定律指出，能量既不会凭空产生，也不会凭空消失，只会转化为不同形式。在力学中，有用能量转移与总输入能量之比称为效率，效率 = 有用能量输出 / 总能量输入。
7. Stress, Strain and the Young Modulus | 应力、应变与杨氏模量
Stress measures the internal force per unit area within a material when it is stretched or compressed. It is calculated as σ = F / A, where F is the applied force and A is the cross-sectional area. The unit is the pascal, Pa, or N m⁻².
应力衡量材料被拉伸或压缩时单位面积上的内力。计算公式为 σ = F / A，其中 F 为施加的力，A 为横截面积。单位是帕斯卡，Pa，或 N m⁻²。
Strain is the extension per unit original length. It is calculated as ε = ΔL / L, where ΔL is the extension and L is the original length. Strain is a ratio and has no units.
应变是每单位原始长度的伸长量。计算公式为 ε = ΔL / L，其中 ΔL 为伸长量，L 为原始长度。应变是一个比值，没有单位。
The Young modulus is the ratio of stress to strain within the elastic limit. It describes the stiffness of a material and is calculated using E = σ / ε = (F / A) / (ΔL / L). Its unit is the pascal, Pa.
杨氏模量是在弹性限度内应力与应变的比值。它描述材料的刚度，计算公式为 E = σ / ε = (F / A) / (ΔL / L)。其单位是帕斯卡，Pa。
The elastic limit is the point beyond which a material no longer returns to its original shape when the load is removed. The limit of proportionality is the point beyond which stress is no longer proportional to strain.
弹性限度是材料在卸载后无法恢复原始形状的临界点。比例限度是应力不再与应变成正比的临界点。
8. Interpreting Stress-Strain Graphs | 应力-应变图像解读
A stress-strain graph for a ductile material such as copper shows a straight line through the origin initially. The gradient of this linear section equals the Young modulus. This is followed by a curved region and then plastic deformation.
铜等延性材料的应力-应变图像最初是一条通过原点的直线。该线性段的斜率等于杨氏模量。之后是曲线区域，然后发生塑性变形。
Brittle materials such as glass obey Hooke’s law until fracture, showing a straight stress-strain graph with little or no plastic deformation. A steep gradient means a high Young modulus and a stiff material.
玻璃等脆性材料在断裂前遵循胡克定律，其应力-应变图像为直线，几乎没有塑性变形。斜率大意味着杨氏模量高，材料刚度大。
Elastic deformation is reversible: the material stores elastic potential energy and returns to its original shape. Plastic deformation is irreversible: the material undergoes permanent changes to its internal structure.
弹性变形是可逆的：材料储存弹性势能并恢复原始形状。塑性变形是不可逆的：材料内部结构发生永久变化。
The area under a force-extension graph gives the work done in stretching the material. For a material obeying Hooke’s law, the elastic potential energy is Eₑ = ½Fx, where x is the extension.
力-伸长量图像下方的面积表示拉伸材料所做的功。对于遵循胡克定律的材料，弹性势能为 Eₑ = ½Fx，其中 x 为伸长量。
9. Fluid Flow and Viscosity | 流体流动与黏度
Fluids can flow in two main ways: laminar flow and turbulent flow. Laminar flow occurs when layers of fluid slide smoothly past each other in parallel lines. Turbulent flow occurs when the fluid moves irregularly, forming eddies and vortices.
流体主要有两种流动方式：层流和湍流。层流是指流体各层沿平行线平滑地相互滑动。湍流是指流体不规则运动，形成漩涡和涡流。
Viscosity is a measure of a fluid’s resistance to flow. A high-viscosity fluid flows more slowly under the same force. The unit of viscosity is the pascal second, Pa s, or N s m⁻².
黏度是衡量流体流动阻力的物理量。相同力的作用下，高黏度流体流动更慢。黏度的单位是帕斯卡秒，Pa s，或 N s m⁻²。
For a small sphere falling through a viscous fluid at terminal velocity, the viscous drag force is given by Stokes’ law, F = 6πηrv, where η is viscosity, r is the radius of the sphere and v is the terminal velocity.
对于在黏性流体中以终极速度下落的小球，黏性阻力由斯托克斯定律给出，F = 6πηrv，其中 η 为黏度，r 为小球半径，v 为终极速度。
At terminal velocity, the resultant force on the falling sphere is zero. This means weight = upthrust + viscous drag. This equation underpins experiments using ball bearing drops to measure viscosity.
在终极速度下，下落小球的合外力为零。这意味着重力 = 浮力 + 黏性阻力。该方程是使用钢球下落实验测量黏度的基础。
10. Core Practical Skills and Exam Pitfalls | 核心实验技能与考试常见误区
In Unit 1 practical questions, you must identify variables, record data with correct precision, plot graphs accurately and calculate gradients using large triangles. Always include units and estimate uncertainties where required.
在第一单元实验题中，你必须识别变量、以正确精度记录数据、准确绘制图像，并使用较大三角形计算斜率。始终标明单位，并在需要时估算不确定度。
A common mistake is confusing displacement with distance, or velocity with speed. Read graph axes carefully: displacement-time gradients give velocity, while velocity-time gradients give acceleration.
一个常见错误是混淆位移与路程，或速度与速率。请仔细阅读图像坐标轴：位移-时间图像斜率表示速度，而速度-时间图像斜率表示加速度。
Another common error is using SUVAT equations when acceleration is not constant. Check the question for phrases such as ‘uniform acceleration’ or ‘constant force’. For changing acceleration, use graph analysis or energy methods instead.
另一个常见错误是在加速度不恒定时使用 SUVAT 方程。检查题目中是否出现“匀加速”或“恒力”等词。如果加速度变化，应改用图像分析或能量方法。
For stress and strain calculations, always use cross-sectional area, not surface area, and original length, not extended length. Convert all units to SI before substituting values into formulas.
在应力和应变计算中，始终使用横截面积而不是表面积，使用原始长度而不是伸长后的长度。代入公式前，请将所有单位换算为国际单位制。
When answering extended responses, structure your answer using definitions, laws, relevant equations and a final conclusion linked to the question context. Clear English and Chinese explanations will help you internalise the logic used in mark schemes.
在回答拓展题时，应使用定义、定律、相关方程以及与题目情境相关的最终结论来组织答案。清晰的中英文解释将帮助你内化评分标准中的逻辑。
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