📚 754 Energy, Work and Power in IGCSE Edexcel Science | 754 IGCSE 爱德思科学中的能量、功与功率
Understanding energy, work and power is fundamental to mastering IGCSE Edexcel Science. This article explores the key concepts you need to know, from energy stores and transfers to calculating work done and efficiency. We will walk through real-world examples and exam-style explanations to help you build a solid foundation.
理解能量、功和功率是掌握 IGCSE 爱德思科学的基础。本文将带你梳理必须掌握的核心概念，从能量储存与转移，到计算做功和效率。我们会借助现实世界的例子和贴近考试的讲解，帮助你打下扎实的基础。
1. What Is Energy? | 什么是能量？
Energy is defined as the capacity to do work. In everyday life, we observe energy in many forms: moving objects possess kinetic energy, hot substances contain thermal energy, and a stretched spring stores elastic potential energy. Energy is a scalar quantity, measured in joules (J).
能量被定义为做功的能力。在日常生活中，我们可以观察到多种形式的能量：运动的物体具有动能、热的物体含有内能（热能）、被拉伸的弹簧存储了弹性势能。能量是标量，单位是焦耳（J）。
2. Energy Stores and How Energy Is Transferred | 能量储存与能量转移方式
In the IGCSE Edexcel specification, we describe energy as being associated with eight energy stores: kinetic, gravitational potential, elastic potential, thermal, chemical, nuclear, magnetic and electrostatic. Energy is transferred between these stores mechanically (by forces), electrically, by heating or by radiation (light and sound).
在 IGCSE 爱德思大纲中，能量与八种能量储存方式相关：动能、重力势能、弹性势能、内能、化学能、核能、磁能和静电能量。能量可以通过机械方式（力的作用）、电的方式、加热或辐射（光和声）在这些储存之间转移。
3. The Principle of Conservation of Energy | 能量守恒定律
Energy can never be created or destroyed; it can only be transferred from one store to another or dissipated. The total energy in a closed system remains constant. This principle helps us analyse any process, from a falling object to an electric circuit.
能量既不能被创造，也不能被消灭；它只能从一种储存转移到另一种储存，或耗散掉。在封闭系统中，总能量保持不变。这一原理帮助我们分析从落体到电路的任何过程。
4. Work Done and Energy Transfer | 做功与能量转移
Work is done whenever a force moves an object through a distance. The work done by a force is equal to the energy transferred. If you push a box across the floor, chemical energy from your muscles is transferred to kinetic energy of the box (and some thermal energy due to friction).
只要力使物体移动一段距离，就做了功。力所做的功等于转移的能量。如果你在地板上推一个箱子，肌肉内的化学能会转移为箱子的动能（以及因摩擦产生的一些内能）。
5. Calculating Work Done | 计算做功的大小
The equation for work done is:
W = F × d
where W is work done in joules (J), F is the force applied in newtons (N), and d is the distance moved in the direction of the force in metres (m). Note that if the force and motion are perpendicular, no work is done.
计算做功的方程为：
W = F × d
其中 W 是做功（焦耳，J），F 是施加的力（牛顿，N），d 是物体沿力的方向移动的距离（米，m）。注意，如果力与运动方向垂直，则不做功。
6. Gravitational Potential Energy (GPE) | 重力势能（GPE）
Gravitational potential energy is the energy stored in an object due to its height above the ground. It is given by:
E_gp = m × g × h
where m is mass (kg), g is the gravitational field strength (on Earth approximately 10 N/kg), and h is height (m). When an object falls, GPE is converted into kinetic energy.
重力势能是物体因为位于地面以上一定高度而储存的能量。其公式为：
E_gp = m × g × h
其中 m 是质量（kg），g 是重力场强（地球表面约为 10 N/kg），h 是高度（m）。当物体下落时，重力势能转化为动能。
7. Kinetic Energy (KE) | 动能（KE）
Kinetic energy is the energy of a moving object. The formula is:
E_k = ½ × m × v²
where m is mass (kg) and v is speed (m/s). This shows that KE is directly proportional to mass and to the square of speed. Doubling the speed quadruples the kinetic energy.
动能是运动物体所具有的能量。其公式为：
E_k = ½ × m × v²
其中 m 是质量（kg），v 是速度（m/s）。这表明动能与质量成正比，与速度的平方成正比。速度增大为原来的两倍，动能会变为原来的四倍。
8. Power – the Rate of Doing Work | 功率——做功的快慢
Power is defined as the rate at which energy is transferred or the rate at which work is done. The equation is:
P = E ÷ t or P = W ÷ t
where P is power in watts (W), E is energy transferred (J), W is work done (J) and t is time taken (s). One watt equals one joule per second. A more powerful appliance transfers more energy each second.
功率被定义为能量转移或做功的快慢。其公式为：
P = E ÷ t 或 P = W ÷ t
其中 P 为功率（瓦特，W），E 是转移的能量（J），W 是做功（J），t 是时间（s）。1 瓦特等于每秒 1 焦耳。功率越大的设备每秒转移的能量就越多。
9. Energy Efficiency and Sankey Diagrams | 能量效率与桑基图
Efficiency tells us how much of the input energy is converted into useful output. It can be calculated using:
Efficiency = (Useful output energy ÷ Total input energy) × 100%
A Sankey diagram represents energy transfers with arrows: the width of each arrow is proportional to the amount of energy. Useful energy goes forward, while wasted energy (often thermal) branches downwards.
效率表明输入能量有多少转化为有用输出。可以使用下面的公式计算：
效率 =（有用输出能量 ÷ 总输入能量）× 100%
桑基图用箭头表示能量转移：每个箭头的宽度与能量多少成正比。有用能量向前，而废能量（通常是内能）向下分支。
10. Energy Resources and Electricity Generation | 能源与发电
Edexcel IGCSE Science expects you to know how different energy resources are used to generate electricity. Non-renewable resources include fossil fuels (coal, oil, natural gas) and nuclear fuel. Renewable resources include solar, wind, tidal, hydroelectric, wave, geothermal and biomass. Most power stations use thermal energy to boil water, producing steam that drives a turbine connected to a generator.
爱德思 IGCSE 科学要求你了解不同能源如何用于发电。不可再生能源包括化石燃料（煤、石油、天然气）和核燃料。可再生能源包括太阳能、风能、潮汐能、水力发电、波浪能、地热能和生物质。大多数发电站利用热能来烧水，产生蒸汽推动汽轮机，带动发电机。
11. Practical Investigation: Measuring Work and Power | 实验探究：测量功和功率
A common investigation involves determining the power of a person running up a flight of stairs. You measure the person’s mass m, the vertical height of the stairs h, and the time taken t. The work done against gravity is W = m × g × h, and power is P = (m × g × h) ÷ t. Repeating the experiment clarifies the relationship between speed and power.
一个常见的探究实验是测量人跑上一段楼梯时的功率。你需要测量人的质量 m、楼梯的垂直高度 h 以及所用时间 t。克服重力所做的功为 W = m × g × h，功率为 P = (m × g × h) ÷ t。重复实验可以明确速度与功率的关系。
12. Common Exam Mistakes and Summary | 常见考试错误与总结
Students often confuse energy, work and power. Remember: work done equals energy transferred, and power is the rate of doing work. Always use the correct units, and check whether a question asks for efficiency as a decimal or a percentage. In energy transfer questions, identify the initial energy store, the final energy store, and how the energy is transferred.
学生常常混淆能量、功和功率。请记住：做功等于转移的能量，而功率是做功的快慢。一定要使用正确的单位，并检查题目要求效率是用小数还是百分数表示。在能量转移的问题中，要先明确初始能量储存、最终能量储存，以及能量是如何转移的。
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