📚 461: Energy, Work and Power: Understanding the Basics | 461: 能量、功和功率基础
Energy, work and power form the backbone of physics. In everyday life we talk about 'using energy' or 'working hard', but in IGCSE science these terms have precise meanings that help us describe how the world behaves. This article unpacks the key ideas from the Edexcel syllabus, linking definitions, equations and real examples so you can tackle exam questions with confidence.
能量、功和功率是物理学的核心概念。在日常生活中，我们常说“消耗能量”或“努力工作”，但在 IGCSE 科学中，这些术语有着精确的定义，能帮助我们描述世界的运行方式。本文依据 Edexcel 考纲，把定义、公式和实际例子串联起来，让你自信应对考试题目。
1. What is Energy? | 什么是能量？
Energy is the ability to do work. It is a scalar quantity measured in joules (J). Energy cannot be created or destroyed, only transferred from one store to another. This conservation law underpins all of physics.
能量是做功的能力。它是一个标量，单位是焦耳 (J)。能量不能凭空产生或消失，只能从一个储存库转移到另一个。这个守恒定律是整个物理学的基础。
2. Forms of Energy | 能量的形式
Energy appears in several forms, often called 'energy stores'. The main stores you need to know for Edexcel IGCSE are kinetic, gravitational potential, elastic potential, chemical, nuclear, thermal (internal), and electrostatic.
能量有多种形式，常被称为“能量储存库”。Edexcel IGCSE 要求学生掌握的主要储存库包括动能、重力势能、弹性势能、化学能、核能、内能 (热能) 和静电势能。
- Kinetic energy – energy of moving objects
- Gravitational potential energy – energy an object has because of its height in a gravitational field
- Elastic potential energy – energy stored when an object is stretched or compressed
- Chemical energy – stored in bonds of chemicals (food, fuels, batteries)
- Nuclear energy – stored inside atomic nuclei, released during fission or fusion
- Thermal (internal) energy – total kinetic and potential energy of particles in a substance
中文对照：动能 – 运动物体的能量；重力势能 – 物体因处于重力场中某一高度而具有的能量；弹性势能 – 物体被拉伸或压缩时储存的能量；化学能 – 储存在化学键中的能量 (食物、燃料、电池)；核能 – 储存在原子核内的能量，在裂变或聚变时释放；内能（热能）– 物体内部所有粒子动能和势能的总和。
3. Energy Transfers and Conservation | 能量转移与守恒
Energy can be transferred between stores via pathways. The four main pathways are: mechanically (by a force doing work), electrically (work done by an electric current), by heating, and by radiation (light or sound). The principle of conservation of energy states that the total energy of a closed system remains constant.
能量可以通过不同路径在储存库之间转移。四种主要转移路径是：通过机械方式（力做功）、通过电流做功、通过加热、以及通过辐射（光或声）。能量守恒定律指出，一个封闭系统的总能量保持不变。
In any energy transfer, some energy is always dissipated (spread out) as thermal energy, making processes less than 100% efficient. This wasted energy is not destroyed, but it becomes harder to use.
在任何能量转移中，总有一部分能量以热能的形式耗散（逸散），导致过程效率不可能达到 100%。这些浪费的能量并没有被消灭，而是变得难以利用。
4. Work Done by a Force | 力做功
Work is done when a force causes an object to move in the direction of the force. It represents a transfer of energy mechanically. If there is no movement, no work is done, even if a force is applied.
当一个力使物体沿力的方向移动时，就做了功。它代表能量的机械转移。如果没有移动，即使施加了力，也不做功。
The equation for work is:
W = F × d
where W is work done in joules (J), F is the force in newtons (N), and d is the distance moved in the direction of the force in metres (m). One joule is defined as the work done when a force of one newton moves an object one metre.
功的公式是：W = F × d，其中 W 表示做功（焦耳 J），F 是力（牛顿 N），d 是物体在力的方向上移动的距离（米 m）。1 焦耳定义为 1 牛顿的力使物体移动 1 米所做的功。
5. Calculating Work: Examples | 计算功的实例
Imagine you push a box with a force of 30 N over a distance of 5 m. The work done is:
设想你用 30 N 的力推动一个箱子移动 5 m。所做的功为：
W = 30 × 5 = 150 J
If the force is not entirely in the direction of motion, only the component of the force parallel to the displacement counts towards work. However, at IGCSE level, questions usually assume force and motion are in the same straight line.
如果力不完全在运动方向上，只有平行于位移的分量才做功。不过在 IGCSE 阶段，题目通常假设力与运动在同一直线上。
6. Gravitational Potential Energy (GPE) | 重力势能 (GPE)
When an object is lifted, work is done against gravity and energy is stored as gravitational potential energy. The GPE gained by an object of mass m raised by height h in a uniform gravitational field is given by:
物体被举高时，克服重力做功，能量以重力势能的形式储存。质量为 m 的物体在均匀重力场中升高 h 后获得的重力势能为：
Eₚ = m × g × h
etres. Lifting a 2 kg object by 3 m on Earth stores about 60 J of GPE (using g = 10 N/kg).
其中 Eₚ 单位为焦耳，m 为千克，g 为重力场强度（地球上约为 10 N/kg 或 9.8 N/kg），h 为米。在地球上将 2 kg 物体举高 3 m 大约储存 60 J 的重力势能。
7. Kinetic Energy (KE) | 动能 (KE)
Any moving object possesses kinetic energy. The kinetic energy of an object depends on its mass and speed, and is calculated by:
任何运动的物体都具有动能。物体的动能取决于它的质量和速度，计算公式为：
Eₖ = ½ × m × v²
where Eₖ is kinetic energy in J, m is mass in kg, and v is speed in m/s. Notice that KE increases with the square of speed: doubling the speed makes the kinetic energy four times larger.
其中 Eₖ 为动能 J，m 为质量 kg，v 为速度 m/s。注意动能随速度的平方增长：速度加倍会使动能变为原来的四倍。
In many IGCSE problems you combine GPE and KE to show energy conservation, e.g. a falling object loses GPE and gains KE.
在许多 IGCSE 题目中，你会结合重力势能和动能来展示能量守恒，例如下落的物体失去重力势能、增加动能。
8. Power: Rate of Energy Transfer | 功率：能量转移速率
Power is the rate at which energy is transferred or work is done. It tells you how quickly energy is being used or converted. A more powerful machine does the same amount of work in less time.
功率是能量转移或做功的速率。它告诉你能量消耗或转化的快慢。功率更大的机器能在更短的时间内完成相同的功。
The formula for power is:
P = ΔE / t or P = W / t
where P is power in watts (W), ΔE is energy transferred in J, W is work done in J, and t is time in seconds. One watt is equal to one joule per second.
功率的公式是 P = ΔE / t 或 P = W / t，其中 P 是功率，单位瓦特 (W)，ΔE 是转移的能量 (J)，W 是做的功 (J)，t 是时间 (s)。1 瓦特等于每秒 1 焦耳。
through 2 m in 4 seconds, the work done is 1000 J, and the power is 1000 J ÷ 4 s = 250 W.
例如，一台电动机在 4 s 内将 500 N 的重物提升 2 m，做功 1000 J，功率为 1000 J ÷ 4 s = 250 W。
9. Energy Efficiency | 能量效率
In real devices, not all energy transferred is useful; some is always wasted, typically as heat. Efficiency measures how well a device converts input energy into useful output energy. It can be expressed as a decimal or a percentage.
在实际装置中，并非所有转移的能量都是有用的；总有一些被浪费，通常以热的形式散失。效率衡量的是装置将输入能量转化为有用输出能量的程度，可用小数或百分比表示。
Efficiency = Useful output energy / Total input energy
wer / Total input power. Since energy cannot be destroyed, the waste energy and useful energy add up to the total input energy.
同样的公式也可以用功率表示：效率 = 有用输出功率 / 总输入功率。由于能量不会消灭，浪费的能量加上有用的能量等于总输入能量。
of light; the remaining 90 J is transferred as heat. Its efficiency is 10/100 = 0.10 or 10%.
例如，一盏灯消耗 100 J 电能，但只发出 10 J 的光能，其余 90 J 转化为热能。其效率为 10/100 = 0.10，即 10%。
10. Sankey Diagrams and Energy Waste | 桑基图与能量浪费
Sankey diagrams are flow diagrams that show energy transfers visually. The width of each arrow is proportional to the amount of energy. Useful energy is drawn as an arrow going straight forward, while wasted energy branches off downwards or upwards. These diagrams help you quickly identify efficiency and energy dissipation.
桑基图是直观展示能量转移的流向图。每根箭头的宽度与能量大小成正比。有用能量画作向前的直箭头，浪费的能量则向下或向上分叉。这类图能帮你快速识别效率和能量耗散情况。
In an exam, you might be asked to draw or interpret a Sankey diagram for a television, an electric motor or a filament bulb. Always check that the total width of input arrows equals the combined width of output arrows, reflecting energy conservation.
考试中可能会要求你画出或解释电视、电动机或白炽灯泡的桑基图。一定要记住：输入箭头的总宽度等于输出箭头的宽度之和，体现能量守恒。
11. Connecting Work, Energy and Power in Exam Questions | 考试中的功、能、功率综合应用
actice using the equations together. For instance, a falling object: GPE lost = KE gained.
典型的 Edexcel IGCSE 题目会要求你计算力所做的功，再求功率，或者利用能量守恒求速度。要练习结合公式。例如下落的物体：减少的重力势能 = 增加的动能。
mgh = ½ mv²
This allows you to find the speed v = √2gh if there is no air resistance. Always show your working step by step, write the correct units, and check that your answer makes sense.
如果没有空气阻力，你可以通过这个关系求得速度 v = √2gh。解题时要逐步展示计算过程，写出正确单位，并检查答案是否合理。
| Quantity | Symbol | Equation | Units |
|---|---|---|---|
| Work | W | F × d | J |
| GPE | Eₚ | mgh | J |
| Kinetic energy | Eₖ | ½ mv² | J |
| Power | P | ΔE / t or W / t | W |
Remember: 1 W = 1 J/s. Time must be in seconds to give power in watts.
记住：1 瓦特 = 1 焦耳/秒。时间必须以秒为单位，功率才能用瓦特表示。
12. Summary and Key Revision Points | 总结与关键复习点
Energy, work and power are linked by a small set of formulas. Memorising them is not enough; you must be able to recognise which energy store is changing in a given scenario, and apply conservation of energy to find unknown quantities. Always convert masses to kilograms, distances to metres, and times to seconds before substituting numbers.
能量、功和功率通过一小套公式相互联系。记忆公式还不够，你必须能够识别在特定场景中哪个能量储存库发生了变化，并应用能量守恒求未知量。代入数字之前，务必将质量换算成千克、距离换算成米、时间换算成秒。
g unless a question specifies 9.8 N/kg. These concepts appear frequently in both Paper 1 and Paper 2 of the Edexcel IGCSE Science exams.
复习时，多多练习绘制桑基图、计算效率，并运用功-能关系。除非题目明确规定 g = 9.8 N/kg，一般使用 10 N/kg。这些概念在 Edexcel IGCSE 科学考试的卷一和卷二中频繁出现。
Published by TutorHao | Edexcel IGCSE Science Revision Series | aleveler.com
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