📚 Physics 1: Forces, Motion and Energy — A Complete Introduction | 物理1：力、运动与能量入门完全指南
Physics is a major branch of the natural sciences, devoted to discovering the fundamental rules that govern matter, energy and the way they interact. It is often called the most basic of the sciences, because it not only explains the phenomena around us but also provides the theoretical framework and the experimental methods on which other subjects, such as chemistry, biology, geology and engineering, are built.
物理学是自然科学的一个重要分支，专注于探索物质与能量及其相互作用的基本规律。它常被视为自然科学的基础，因为物理学不仅能解释我们身边发生的各种现象，还为化学、生物、地质、工程等其他学科奠定了理论框架与实验方法。
The study of physics covers an extremely wide range of topics, and within that range Physics 1 serves as the entry-level course. It gives students a solid grounding in physical knowledge and concepts, and helps them understand and explain natural phenomena together with the scientific principles behind them. This article follows the standard content of a first physics course and pairs every key idea with its Chinese explanation.
物理学的研究领域极为广阔，可细分为众多方向，其中物理1是入门课程。它为学生打下坚实的物理知识与概念基础，帮助他们领悟并阐释自然界的各种现象及其背后的科学原理。本文按照物理1的标准内容展开，并对每一个核心知识点给出中英对照讲解。
1. Physics as a Foundational Science | 物理学：自然科学的基础
Physics asks the deepest questions that can be asked about the material world: why objects fall, why a spring returns to its original length, why the Moon keeps circling the Earth, and how energy moves from one store to another. Because its laws apply to atoms, to galaxies and to everything in between, physics supplies the vocabulary and the mathematical tools that other sciences borrow. A biologist studying the flow of blood through a vessel is really solving a fluid-mechanics problem; a chemist studying bond energy is really using the idea of electrostatic potential energy.
物理学追问的是关于物质世界最深层的问题：物体为什么会下落，弹簧为什么能恢复原长，月球为什么持续绕地球运行，能量又是如何在不同形式之间转移的。由于物理定律既适用于原子，也适用于星系，还适用于介于两者之间的一切事物，因此其他学科往往会借用物理学的语言与数学工具。研究血液在血管中流动的生物学家，本质上是在解决一个流体力学问题；研究键能的化学家，本质上是在使用静电势能的概念。
Physics = Matter + Energy + Interactions
This is exactly why Physics 1 matters beyond the physics classroom. It is not a collection of isolated formulas to memorise, but a way of thinking: identify the system, draw a diagram, write down the relevant law, and check whether the answer is reasonable.
这正是物理1的意义超出物理课堂本身的原因。它不是一堆需要死记硬背的孤立公式，而是一种思维方式：确定研究对象、画出受力图、写出相关定律、最后检验答案是否合理。
2. What Physics 1 Is and Who Takes It | 物理1是什么、适合谁学习
Physics 1 is the introductory course of the physics sequence. It usually appears in the first year of A Level, AP, IB or senior high school programmes, and it assumes only basic algebra and trigonometry — no calculus is required. Its purpose is to build a working vocabulary of physical quantities and the conceptual framework needed to interpret natural phenomena and their scientific principles.
物理1是物理课程体系的入门课。它通常出现在 A Level、AP、IB 或高中课程的第一年，只要求学生掌握基础代数与三角学，不需要微积分。它的目的，是帮助学生建立起一套可用的物理量词汇，并形成解释自然现象及其科学原理的概念框架。
Typical students include future engineers, medical students, computer scientists and economists, as well as those who simply want a rigorous science subject. What unites them is not a career plan but a willingness to reason quantitatively about the world.
学习这门课的学生通常包括未来的工程师、医学生、计算机科学家和经济学者，也包括单纯希望修读一门严谨理科课程的同学。把他们联系在一起的并不是职业规划，而是愿意用定量的方式去思考世界。
3. Core Concepts and Quantities in Physics 1 | 物理1的核心概念与物理量
In Physics 1 students meet force, motion, speed, acceleration, mass and energy as the central quantities of mechanics. Every one of them has a precise definition, a symbol, a unit and — crucially — a physical meaning that can be tested experimentally.
在物理1中，学生将接触到力、运动、速度、加速度、质量和能量等力学核心概念。每一个概念都拥有精确定义、专属符号、对应单位，更重要的是，它们都具有可以通过实验检验的物理含义。
- Mass (m) — a measure of how much matter an object contains and of its resistance to acceleration; unit: kilogram (kg).
质量（m）——衡量物体所含物质的多少，也衡量其抵抗加速的能力；单位：千克（kg）。 - Force (F) — a push or a pull that can change an object's shape, speed or direction; unit: newton (N).
力（F）——能够改变物体形状、速度或方向的推或拉；单位：牛顿（N）。 - Speed and velocity (v) — speed is how fast something moves; velocity is speed together with a direction.
速率与速度（v）——速率描述运动的快慢；速度则是速率加上方向。 - Acceleration (a) — the rate of change of velocity; unit: metre per second squared (m s⁻²).
加速度（a）——速度的变化率；单位：米每二次方秒（m s⁻²）。 - Energy (E) — the capacity to do work; unit: joule (J).
能量（E）——做功的本领；单位：焦耳（J）。
Notice how tightly these ideas are interlocked: force changes motion, changing motion involves acceleration, and acceleration over a distance transfers energy.
可以看到，这些概念彼此紧密关联：力改变运动状态，运动状态的改变涉及加速度，而加速度在位移上的累积又伴随能量的转移。
4. Units, Symbols and Measurement | 单位、符号与测量
Reliable physics begins with reliable measurement. Physics 1 introduces the SI system, the prefixes that scale it, and the difference between base units and derived units. It also introduces the distinction between scalars, which have magnitude only, and vectors, which have both magnitude and direction.
可靠的物理始于可靠的测量。物理1会介绍国际单位制（SI）、用于缩放单位的前缀，以及基本单位与导出单位的区别；同时还会介绍标量与矢量的差别——标量只有大小，矢量既有大小又有方向。
| Quantity | Symbol | SI Unit |
| Mass | m | kilogram, kg |
| Displacement | s | metre, m |
| Time | t | second, s |
| Velocity | v | m s⁻¹ |
| Acceleration | a | m s⁻² |
| Force | F | newton, N = kg m s⁻² |
| Energy | E | joule, J = N m |
Common prefixes worth memorising are k (10³), c (10⁻²), m (10⁻³), μ (10⁻⁶) and n (10⁻⁹). Students should also state the uncertainty of a measurement and quote an answer to a sensible number of significant figures, because a number without an uncertainty is only half a result.
值得记住的常用前缀包括 k（10³）、c（10⁻²）、m（10⁻³）、μ（10⁻⁶）和 n（10⁻⁹）。学生还应说明测量结果的不确定度，并按合理的有效数字报告答案，因为一个没有不确定度的数值只算半个结果。
5. Describing Motion: Distance, Speed and Acceleration | 描述运动：路程、速率与加速度
Kinematics is the language used to describe motion without yet asking what causes it. Distance is a scalar; displacement is the straight-line change of position and is a vector. Average speed is total distance divided by total time, while instantaneous speed is the value at a single moment. Acceleration is defined as the rate of change of velocity.
运动学是用以描述运动的语言，此时还不追问运动的原因。路程是标量，位移是位置的直线变化量，属于矢量。平均速率等于总路程除以总时间，瞬时速率则是某一时刻的速率。加速度定义为速度的变化率。
a = Δv ÷ Δt
If velocity changes by 12 m s⁻¹ in 4 s, the acceleration is 3 m s⁻². A negative acceleration simply means the acceleration points opposite to the chosen positive direction — it does not automatically mean the object is slowing down.
如果速度在 4 s 内变化了 12 m s⁻¹，则加速度为 3 m s⁻²。加速度为负值只是说明加速度方向与所选正方向相反，并不自动意味着物体正在减速。
6. Motion Graphs and the Equations of Motion | 运动图像与运动方程
Graphs are one of the most powerful tools in Physics 1. On a displacement-time graph the gradient gives velocity; on a velocity-time graph the gradient gives acceleration, and the area between the line and the time axis gives the displacement. A straight, sloping line on a velocity-time graph means uniform acceleration.
图像是物理1中最有力的工具之一。在位移—时间图像中，斜率表示速度；在速度—时间图像中，斜率表示加速度，图线与时间轴之间的面积表示位移。速度—时间图像上的一条倾斜直线代表匀加速运动。
For motion with constant acceleration, four equations link the five quantities u, v, a, s and t:
对于匀加速直线运动，有四个方程把 u、v、a、s、t 这五个量联系起来：
v = u + at
s = ut + ½at²
v² = u² + 2as
s = ½(u + v)t
sing v = u + at gives v = 0 + 2 × 5 = 10 m s⁻¹, and using s = ut + ½at² gives s = 0 + ½ × 2 × 5² = 25 m.
选择正确的方程，关键在于先列出已知量和待求量。例如，一辆汽车从静止开始以 2 m s⁻² 匀加速 5 s：由 v = u + at 得 v = 0 + 2 × 5 = 10 m s⁻¹；由 s = ut + ½at² 得 s = 0 + ½ × 2 × 5² = 25 m。
7. Newton's First Law and Inertia | 牛顿第一定律与惯性
Newton's first law states that an object with no resultant force acting on it either stays at rest or continues to move in a straight line at constant velocity. This property of resisting changes in motion is called inertia, and it depends on mass: the greater the mass, the greater the inertia.
牛顿第一定律指出，当物体不受合外力作用时，它将保持静止，或继续做匀速直线运动。这种抵抗运动状态改变的性质称为惯性，而惯性取决于质量：质量越大，惯性越大。
The law is easy to state and easy to misapply. A book resting on a table has two forces acting on it — weight downwards and the normal contact force upwards — and they cancel, so the resultant force is zero and the book stays at rest. In a moving vehicle, passengers keep moving forward when the brakes are applied, not because a forward force appears out of nowhere, but because no force acts to slow them down.
这条定律表述简单，却容易被误用。放在桌上的书受到两个力——向下的重力和向上的支持力——两者相互抵消，合外力为零，所以书保持静止。在行驶的车辆中急刹车时，乘客会继续前倾，这并不是凭空出现了一个向前的力，而是因为没有力去让他们减速。
8. Newton's Second Law: Force, Mass and Acceleration | 牛顿第二定律：力、质量与加速度
The second law describes the relationship between acceleration and the resultant external force. The acceleration of an object is directly proportional to the resultant force and inversely proportional to its mass, and it points in the same direction as the resultant force.
牛顿第二定律描述了加速度与合外力之间的关系：物体的加速度与合外力成正比，与质量成反比，且方向与合外力方向相同。
F = ma
ht is simply the gravitational force acting on a mass, so W = mg, where g ≈ 9.81 m s⁻² near the Earth's surface.
由于 F 和 a 都是矢量，这个方程通常需要在两个相互垂直的方向上分别使用，常见的是水平方向与竖直方向。重力就是作用在质量上的引力，因此 W = mg，在地表附近 g ≈ 9.81 m s⁻²。
the motion, the resultant force becomes 10 − 4 = 6 N and the acceleration falls to 3 m s⁻².
例题：一辆 2 kg 的小车在无摩擦轨道上受到 10 N 的拉力，则 a = F ÷ m = 10 ÷ 2 = 5 m s⁻²。若存在 4 N 的摩擦力阻碍运动，则合外力变为 10 − 4 = 6 N，加速度降为 3 m s⁻²。
9. Newton's Third Law and Action-Reaction Pairs | 牛顿第三定律与作用力—反作用力
The third law states that forces always arise in pairs: for every action there is an equal and opposite reaction. If A exerts a force on B, then B exerts on A a force of the same magnitude acting along the same line but in the opposite direction.
牛顿第三定律指出，力总是成对出现：每一个作用力都伴随一个大小相等、方向相反的反作用力。若 A 对 B 施加一个力，则 B 也会沿同一直线对 A 施加大小相等、方向相反的力。
The critical detail is that the two forces act on different objects, which is why they never cancel each other. When a swimmer pushes water backwards, the water pushes the swimmer forwards; when a rocket expels gas downwards, the gas pushes the rocket upwards. Also note that action and reaction forces must be of the same type — both gravitational, both contact, and so on.
关键的细节在于：这两个力作用在不同物体上，因此永远不会相互抵消。游泳者向后推水，水就向前推游泳者；火箭向下喷出气体，气体就向上推火箭。还要注意，作用力与反作用力必须属于同一类型——同为引力，或同为接触力，等等。
10. Free Fall and Simple Harmonic Motion | 自由落体与简谐振动
th air resistance neglected; all objects then fall with the same acceleration g ≈ 9.81 m s⁻², independent of mass.
物理1还会介绍贯穿整个学科的两个简单运动模型。自由落体是指物体只受重力作用的运动（忽略空气阻力）；此时所有物体都以相同的加速度 g ≈ 9.81 m s⁻² 下落，与质量无关。
v = gt h = ½gt²
Simple harmonic motion (SHM) describes vibration about an equilibrium position where the restoring force is proportional to the displacement and directed back towards equilibrium. Springs and pendulums are the classic examples.
简谐振动（SHM）描述的是围绕平衡位置的振动，其恢复力与位移成正比，方向始终指向平衡位置。弹簧和单摆是最经典的例子。
F = −kx T = 2π√m ÷ k T = 2π√L ÷ g
ngth and T the period of one complete oscillation. Students learn how to analyse an object' gravity, and how vibrating systems obey these rules; stretching a spring also obeys Hooke's law, F = kx, within its elastic limit.
其中 k 为劲度系数，m 为悬挂物体的质量，L 为摆长，T 为一次完整振动的周期。学生将学习如何分析重力作用下的物体运动，以及弹簧、单摆等振动系统所遵循的规律；在弹性限度内拉伸弹簧也遵循胡克定律 F = kx。
11. Work, Energy and Energy Transformations | 功、能量与能量转化
Beyond basic mechanics, the course introduces energy and work. Work is done when a force moves an object along its own direction, and the amount of work equals the energy transferred.
除了基础力学，课程还涉及能量与功的概念。当力使物体沿力的方向发生位移时，就做了功，而做功的多少等于所转移的能量。
W = Fs cos θ KE = ½mv² GPE = mgh
Students explore kinetic energy and potential energy, how they transform into one another, and how to calculate the work done on an object and how that work drives a change in energy. In a closed system the total energy is conserved, which is why a falling ball speeds up as its gravitational potential energy becomes kinetic energy, and why a pendulum swings back to nearly its starting height.
学生将探索动能、势能等不同能量形式及其相互转化，并掌握计算物体所做功的方法，以及功如何驱动能量变化。在封闭系统中总能量守恒，这正是下落小球的重力势能转化为动能后速度变快的原因，也是单摆能几乎回到起始高度的原因。
, measured in watts, and efficiency is useful output energy divided by total input energy.
效率与功率延伸了同一思路：功率是能量转移的速率，P = W ÷ t，单位为瓦特；效率等于有用输出能量除以总输入能量。
12. Practical Work, Exam Skills and What Comes Next | 实验、考试技能与后续学习
Physics 1 contains a practical element that lets students test theory through observation and measurement. Typical experiments include measuring g with light gates or a ticker-timer, verifying Hooke's law with a spring and masses, studying the period of a pendulum against its length, and investigating Newton's second law with a trolley and pulleys. These activities deepen understanding of physical principles and also develop experimental technique and scientific thinking.
物理1包含实验环节，让学生通过观察和测量来验证理论。典型实验包括：用光电门或打点计时器测量重力加速度 g；用弹簧和砝码验证胡克定律；研究单摆周期与摆长的关系；用小车和滑轮研究牛顿第二定律。这些实践不仅能深化对物理原理的认识，还有助于培养实验技巧和科学思维能力。
Good practice in the examined papers means writing down the equation before substituting numbers, keeping units throughout, drawing clear free-body diagrams, and commenting on sources of error such as reaction time, friction and parallax. Students should also be comfortable rearranging equations and converting units before starting a calculation.
在考试作答中，良好习惯包括：先写出方程再代入数值、全程带上单位、画出清晰的受力分析图，并说明反应时间、摩擦、视差等误差来源。开始计算前，学生还应熟练地进行公式变形和单位换算。
By the end of the course, students have gained a coherent set of physical concepts and problem-solving tools. This lays a solid foundation for advanced physics courses, or for applying physics within other scientific fields such as engineering, materials science and medicine — whether the next step is A2, IB Higher Level, AP Physics 2 or a first-year university module.
通过这门课程的学习，学生将收获一套完整的物理概念和解题工具。这为他们后续研修高级物理课程，或在工程、材料科学、医学等其他科学领域应用物理学奠定了扎实根基——无论下一步是 A2、IB 高阶、AP 物理2，还是大学一年级的物理模块。
In summary, Physics 1 is a fascinating journey of discovery: by investigating the relationship between matter and energy, it reveals how the natural world works. It offers a new perspective and trains analytical thinking and experimental skills. Whatever a student's interests may be, Physics 1 opens the door to the wider world of physics.
总而言之，物理1是一趟引人入胜的知识之旅：通过探究物质与能量的关联，它揭示了自然界的运行机制。它不仅提供了一个全新视角，也锻炼了分析思维与实验技能。不论学生兴趣何在，物理1都能开启通往更广阔物理世界的大门。
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