current
EN: Electric current is the rate at which electric charge flows through a conductor. - Unit: ampere (A). - Current in a circuit is associated with energy transfer; devices transform electrical energy into other forms.
中文：电流是电荷通过导体的流动速率。 - 单位：安培（A）。 - 电路中的电流对应能量的传递，用电器把电能转化为其他形式。
mass
EN: Mass is the amount of matter in an object and a measure of its inertia (resistance to changes in motion). - Unit: kilogram (kg). - In this Topic, mass affects both KE (1/2 mv^2) and GPE (m g Δh) linearly.
中文：质量表示物体所含物质的多少，也是惯性大小的量度（抗拒运动状态改变的能力）。 - 单位：千克（kg）。 - 在本主题中，质量会线性影响动能（1/2 mv^2）和重力势能（m g Δh）。
acceleration due to gravity
EN: Acceleration due to gravity (g) near Earth is about 9.8 m/s^2. - It is the acceleration of a freely falling object (ignoring air resistance). - g is used in gravitational potential energy: GPE = m g Δh.
中文：近地面重力加速度 g ≈ 9.8 m/s^2。 - 忽略空气阻力时，自由落体的加速度约为 g。 - 在重力势能公式中使用：GPE = m g Δh。
change in height
EN: Change in height (Δh) is the difference between final and initial height. - It tells how much gravitational potential energy changes: ΔGPE = m g Δh. - Δh depends on the chosen reference level and can be positive or negative.
中文：高度变化（Δh）是末高度与初高度之差。 - 它决定重力势能的变化：ΔGPE = m g Δh。 - Δh 与所选参考高度有关，可为正也可为负。
velocity
EN: Velocity is speed with direction (a vector). - Unit: metres per second (m/s). - Because KE ∝ v^2, doubling velocity makes kinetic energy 4 times larger (if mass is the same).
中文：速度（velocity）是带方向的速率（矢量）。 - 单位：米每秒（m/s）。 - 因为动能与 v^2 成正比，同质量时速度加倍，动能会变为 4 倍。
kilojoules
EN: A kilojoule (kJ) is 1000 joules. - We often use kJ because the joule is a small unit in everyday situations.
中文：千焦（kJ）= 1000 焦耳（J）。 - 由于焦耳较小，生活和化学/食品能量等常用千焦表示。
joule (J)
EN: The joule (J) is the SI unit of energy. - 1 J = 1 N·m = 1 kg·m^2/s^2. - Rough sense of scale: lifting a 0.10 kg object by 1 m requires about 1 J of gravitational potential energy.
中文：焦耳（J）是能量的国际单位。 - 1 J = 1 N·m = 1 kg·m^2/s^2。 - 直观尺度：把约 0.10 kg 的物体抬高 1 m，大约需要 1 J 的重力势能。
ultraviolet radiation
EN: Ultraviolet (UV) radiation is electromagnetic radiation with wavelengths shorter than visible violet light. - UV photons have relatively high energy and can cause chemical changes (e.g., sunburn).
中文：紫外线（UV）是波长比紫光更短的电磁辐射。 - 紫外光子能量较高，可能引起化学变化（如晒伤）。
efficient
EN: An energy transformation is efficient if a large fraction of the input energy becomes useful output. - Efficiency = (useful output energy) / (input energy) × 100%. - Real systems are never 100% efficient because some energy becomes unwanted thermal/sound energy due to friction and resistance.
中文：能量转化“高效”表示输入能量中有较大比例变成了有用的输出。 - 效率 = 有用输出能量 / 输入能量 × 100%。 - 真实系统不可能 100% 高效，因为摩擦/电阻等会使部分能量转为不想要的热能/声能。
friction
EN: Friction is a force that opposes motion between surfaces (or through air/water). - Friction converts mechanical energy into less useful forms, mainly thermal energy (and sometimes sound). - This is why motion usually slows down without additional energy input.
中文：摩擦力是阻碍相对运动的力（包括表面摩擦和空气/水阻力）。 - 摩擦会把机械能转化为较难利用的热能（有时还有声能）。 - 因此没有持续能量输入时，运动往往会逐渐减慢。
sound energy
EN: Sound energy is energy carried by vibrations (mechanical waves) traveling through matter. - Sound requires a medium (air, water, solids) and cannot travel through a vacuum. - When absorbed, sound energy often transforms into thermal energy.
中文：声能是由振动产生并通过介质传播的机械波所携带的能量。 - 声音需要介质（空气/水/固体），真空中不能传播。 - 被吸收后通常转化为热能。
radiant energy
EN: Radiant energy is energy carried by electromagnetic radiation (waves/photons). - It includes visible light, infrared, and ultraviolet. - When absorbed by matter, radiant energy often transforms into thermal energy.
中文：辐射能是由电磁辐射（电磁波/光子）携带的能量。 - 包括可见光、红外线、紫外线等。 - 被物质吸收后常转化为热能。
infrared
EN: Infrared is electromagnetic radiation with wavelengths longer than visible red light. - It is often experienced as warmth because absorbing infrared increases thermal energy.
中文：红外线是波长比红光更长的电磁辐射。 - 常被感受到“热”，因为吸收红外线会增加物体的热能。
nuclear energy
EN: Nuclear energy is energy stored in atomic nuclei. - It can be released by fission, fusion, or radioactive decay. - Nuclear energy has a very high energy density compared with chemical energy.
中文：核能是储存在原子核中的能量。 - 可通过核裂变、核聚变或放射性衰变释放。 - 相比化学能，核能的能量密度非常高。
magnetic potential energy
EN: Magnetic potential energy is stored due to the position/orientation of magnets in a magnetic field. - If released, this stored energy can transform into kinetic energy as objects move.
中文：磁势能是由磁体在磁场中的位置/方向而储存的能量。 - 释放后可转化为动能，使物体发生运动。
Heat
EN: Heat is thermal energy that is transferred from a warmer object to a cooler one because of a temperature difference. - Heat is energy in transit (not a substance stored inside an object). - Unit: joule (J).
中文：热量是由于温度差从高温物体传递到低温物体的热能。 - 热量强调“传递中的能量”，不是物体内部的一种“物质”。 - 单位：焦耳（J）。
thermal energy
EN: Thermal energy is the total kinetic energy of the particles in matter (microscopic motion). - Generally, higher temperature means greater average particle kinetic energy. - Thermal energy can be transferred as heat when there is a temperature difference.
中文：热能（更准确地说是与温度有关的内能部分）来自物质内部粒子的微观运动动能总和。 - 温度越高，粒子平均动能越大。 - 有温差时，热能会以“热量”的形式传递。
electrical potential energy
EN: Electrical potential energy is stored energy due to separated electric charges (electric potential difference/voltage). - A battery stores electrical potential energy and can transfer it to a circuit. - In a circuit it can transform into other forms (light, thermal, sound, motion).
中文：电势能是由于电荷分离而储存的能量（与电势差/电压有关）。 - 电池储存电势能，并可把能量传递到电路中。 - 在电路中可转化为光、热、声或机械运动等其他形式。
electrical kinetic energy
EN: Electrical kinetic energy refers to the energy associated with moving electric charges (electric current). - When charges move through a device, the energy can transform into light, heat, or motion.
中文：电荷运动（电流）所携带的能量可理解为“电的动能”。 - 电流通过用电器时，能量可以转化为光、热或机械运动等。
chemical potential energy
EN: Chemical potential energy is stored in chemical bonds. - Fuels, food, and batteries store chemical potential energy. - During chemical reactions it can transform into thermal, radiant (light), electrical, and mechanical energy.
中文：化学势能是储存在化学键中的能量。 - 燃料、食物、电池都储存化学势能。 - 化学反应中它可转化为热能、光（辐射）能、电能、机械能等。
gravitational potential energy
EN: Gravitational potential energy (GPE) is energy stored because of height in a gravitational field. - It depends on mass, gravitational field strength (g), and change in height. - Near Earth: GPE = m g Δh (relative to a chosen reference level).
中文：重力势能（GPE）是物体由于处在重力场中的高度而具有的能量。 - 与质量、重力加速度 g，以及高度变化 Δh 有关。 - 近地面常用：GPE = m g Δh（相对于所选参考高度）。
mechanical kinetic energy
EN: Mechanical kinetic energy is the kinetic energy of the motion of objects (macroscopic motion you can observe). - It depends on mass and velocity: KE = 1/2 mv^2. - It is different from thermal energy, which is microscopic particle motion.
中文：机械动能（机械运动的动能）是可观察到的物体整体运动所具有的动能。 - 与质量和速度有关：KE = 1/2 mv^2。 - 它不同于热能；热能来自微观粒子的无规则运动。
energy
EN: Energy is the ability to cause change in a system or do work. - Energy appears in different forms (mechanical, thermal, chemical, electrical, radiant, etc.). - Energy can be transferred between a system and its surroundings, or transformed from one form to another. - The SI unit of energy is the joule (J).
中文：能量是使系统发生变化或对物体做功的能力。 - 能量有多种形式（机械、热、化学、电、辐射等）。 - 能量既可以在系统与环境之间传递，也可以在不同形式之间转化。 - 能量的国际单位是焦耳（J）。
system
EN: A system is the part of the universe you choose to study (the object(s) under observation). - The system boundary is defined by you, depending on the question you are trying to answer. - Energy can enter/leave the system, so tracking the system helps you describe energy transfers.
中文：系统是你选择研究的那一部分宇宙（被观察/被分析的对象或对象集合）。 - 系统边界由研究者根据问题来定义，可大可小。 - 能量可以在系统与环境之间传递，因此先定义系统有助于分析能量变化。
potential energy
EN: Potential energy is stored energy due to position or configuration. - It can be transformed into kinetic energy and other forms. - Examples include gravitational, chemical, electrical, and magnetic potential energy.
中文：势能是由于位置或结构/状态而“储存”的能量。 - 势能可以转化为动能以及其他形式的能量。 - 常见类型：重力势能、化学势能、电势能、磁势能等。
kinetic energy
EN: Kinetic energy is the energy of motion. Anything that is moving has kinetic energy. - For a moving object, kinetic energy depends on mass and velocity. - In many Grade-10 problems: KE = 1/2 mv^2 (always ≥ 0).
中文：动能是由于运动而具有的能量，任何在运动的物体都有动能。 - 动能与质量和速度有关。 - 常用公式：KE = 1/2 mv^2（动能一定是非负的）。
law of conservation of energy
EN: The law of conservation of energy states that energy cannot be created or destroyed. - Total energy stays constant in an isolated system. - What changes is the form of energy and where it is (system vs. surroundings). - Some transformed energy becomes less useful (often as thermal energy and sound) due to friction and other processes.
中文：能量守恒定律：能量不会凭空产生，也不会凭空消失。 - 对于孤立系统，总能量保持不变。 - 改变的是能量的形式以及能量所在的位置（系统或环境）。 - 由于摩擦等原因，部分能量会转化为较难利用的热能/声能，但总量仍守恒。
surroundings
EN: The surroundings are everything outside the system boundary. - Surroundings can interact with the system by transferring energy (and sometimes matter). - In many problems, you only include the nearby surroundings that actually interact.
中文：环境（周围环境）是系统边界之外的所有事物。 - 环境可以通过能量（有时也包括物质）与系统发生相互作用。 - 解题时通常只考虑与系统有实际相互作用的那部分环境。