📚 Energy Transfers | 能量转换
Energy is a fundamental concept in science. It allows things to happen, from the movement of a car to the growth of a plant. In the IGCSE Edexcel Science course, understanding how energy is transferred and transformed is essential across physics, chemistry, and biology.
能量是科学中的一个基本概念。它使事物得以发生，从汽车的行驶到植物的生长。在 Edexcel IGCSE 科学课程中，理解能量如何转移和转化是物理、化学和生物学的核心内容。
1. Forms of Energy | 能量的形式
Energy exists in many different forms. The main ones you need to know are: kinetic (movement), potential (stored), thermal (heat), chemical, electrical, light, sound, nuclear, and elastic potential.
能量以多种不同形式存在。你需要掌握的主要形式有：动能（运动）、势能（储存）、热能（热）、化学能、电能、光能、声能、核能和弹性势能。
- Kinetic energy is the energy an object has because of its motion.
- 动能是物体因运动而具有的能量。
- Potential energy is stored energy, such as gravitational or elastic potential energy.
- 势能是储存的能量，例如引力势能或弹性势能。
- Chemical energy is stored in bonds between atoms and is released in reactions.
- 化学能储存在原子之间的化学键中，并在反应中释放。
- Electrical energy is carried by moving charges in a circuit.
- 电能由电路中移动的电荷携带。
- Light and sound are forms of energy that travel as waves.
- 光能和声能是以波的形式传播的能量。
Everyday examples: a moving football has kinetic energy; a stretched rubber band has elastic potential energy; a battery stores chemical energy.
日常例子：滚动的足球具有动能；拉伸的橡皮筋具有弹性势能；电池储存化学能。
2. The Law of Conservation of Energy | 能量守恒定律
The law of conservation of energy states that energy cannot be created or destroyed, only transferred or transformed from one form to another. The total amount of energy in a closed system remains constant.
能量守恒定律指出：能量既不能被创造，也不能被消灭，只能从一种形式转移或转化为另一种形式。在封闭系统中，能量的总量保持不变。
总能量（前） = 总能量（后）
For example, when a ball is dropped, gravitational potential energy is converted into kinetic energy and a little thermal energy due to air resistance. The total energy before and after remains the same.
例如，当球下落时，引力势能转化为动能，并因空气阻力而转化出少量热能。前后总能量保持不变。
- Energy can be transferred usefully, or wasted (dissipated) as thermal energy.
- 能量可以被有效转移，也可能以热能形式被浪费（耗散）。
- In any energy transfer, the useful energy output plus wasted energy equals the total energy input.
- 在任何能量转移中，有用能量输出加上浪费的能量等于总能量输入。
3. Work and Power | 功与功率
Work is done when a force causes an object to move in the direction of the force. The amount of work done is equal to the energy transferred.
当力使物体沿力的方向移动时，就做了功。做功的多少等于转移的能量。
功 (J) = 力 (N) × 距离 (m)
Work is measured in joules (J). One joule is the work done when a force of one newton moves an object one metre.
功的单位是焦耳（J）。1 焦耳等于 1 牛顿的力使物体移动 1 米所做的功。
Power is the rate at which energy is transferred or work is done. It is measured in watts (W).
功率是能量转移或做功的速率。单位是瓦特（W）。
功率 (W) = 功 (J) ÷ 时间 (s)
- A power of 1 watt means 1 joule of energy is transferred every second.
- 1 瓦特表示每秒转移 1 焦耳的能量。
- Example: a 60 W bulb transfers 60 joules of electrical energy per second, mostly as light and heat.
- 例如：一个 60 W 的灯泡每秒转移 60 焦耳电能，大部分转化为光能和热能。
4. Kinetic and Potential Energy | 动能与势能
Kinetic energy depends on the mass and speed of an object. The faster an object moves or the heavier it is, the more kinetic energy it has.
动能取决于物体的质量和速度。物体运动越快或质量越大，其动能就越大。
Eₖ = ½mv²
In this equation, Eₖ is kinetic energy in joules, m is mass in kilograms, and v is speed in metres per second.
在这个公式中，Eₖ 是动能（单位：焦耳），m 是质量（单位：千克），v 是速度（单位：米/秒）。
Gravitational potential energy is the energy an object has due to its height above the ground.
引力势能是物体由于高于地面而具有的能量。
Eₚ = mgh
Here, Eₚ is gravitational potential energy, m is mass, g is gravitational field strength (approximately 10 N/kg on Earth), and h is height.
其中，Eₚ 是引力势能，m 是质量，g 是重力场强度（地球上约为 10 N/kg），h 是高度。
- When an object falls, Eₚ decreases and Eₖ increases.
- 当物体下落时，引力势能减少，动能增加。
- In a pendulum, energy transfers between kinetic and potential energy repeatedly.
- 在摆锤中，能量在动能和势能之间反复转化。
5. Thermal Energy Transfer | 热能传递
Thermal energy can be transferred by three main processes: conduction, convection, and radiation.
热能可以通过三种主要方式传递：传导、对流和辐射。
- Conduction is the transfer of heat through a material without the material moving. It happens mainly in solids.
- 传导是热量通过材料传递而材料本身不移动，主要发生在固体中。
- Convection is the transfer of heat by the movement of fluids (liquids or gases) due to density changes.
- 对流是通过流体（液体或气体）因密度变化而运动来传递热量。
- Radiation is the transfer of heat by infrared waves, which can travel through a vacuum.
- 辐射是通过红外线波传递热量，可以穿过真空。
Dark, matt surfaces are better at absorbing and emitting radiation than light, shiny surfaces. This is why solar panels are often dark in colour.
深色粗糙表面比浅色光滑表面更能吸收和发射辐射。这就是太阳能板通常呈深色的原因。
In everyday life, a vacuum flask reduces all three types of heat transfer to keep drinks hot or cold.
在日常生活中，保温瓶通过减少这三种热传递来保持饮料的热度或冷度。
6. Energy in Food | 食物中的能量
Food contains chemical energy stored in carbohydrates, fats, and proteins. When our bodies digest food, this energy is released for growth, movement, and maintaining body temperature.
食物中的碳水化合物、脂肪和蛋白质储存着化学能。当身体消化食物时，这些能量被释放，用于生长、运动和维持体温。
The energy content of food is measured in kilojoules (kJ) or kilocalories (kcal). A common way to measure it is using a calorimeter.
食物中的能量以千焦（kJ）或千卡（kcal）为单位。常用的测量方法是用热量计。
能量 = 水的质量 × 比热容 × 温度变化
- Fats provide about 37 kJ per gram, while carbohydrates and proteins provide about 17 kJ per gram.
- 脂肪每克约提供 37 kJ 能量，而碳水化合物和蛋白质每克约提供 17 kJ。
- Different foods have different energy densities.
- 不同食物具有不同的能量密度。
- Energy balance: energy input from food should equal energy output from activity to maintain a stable weight.
- 能量平衡：从食物摄入的能量应与活动消耗的能量相等，以保持体重稳定。
7. Energy Resources | 能源资源
Energy resources can be classified as renewable or non-renewable. Non-renewable resources such as coal, oil, and natural gas are finite and produce carbon dioxide when burned.
能源资源可分为可再生能源和不可再生能源。煤、石油和天然气等不可再生资源是有限的，燃烧时会产生二氧化碳。
Renewable resources include solar, wind, hydroelectric, geothermal, wave, and tidal. They are replenished naturally and generally produce less pollution.
可再生能源包括太阳能、风能、水能、地热能、波浪能和潮汐能。它们能自然补充，通常产生更少的污染。
| Resource | Advantages | Disadvantages |
| Solar | Free and abundant | Dependent on weather and daylight |
| Wind | Clean and renewable | Unreliable; visual and noise pollution |
| Fossil fuels | Reliable and high energy content | Contribute to climate change; finite |
In IGCSE Science, you should be able to compare renewable and non-renewable sources in terms of reliability, environmental impact, and cost.
在 IGCSE 科学中，你需要能够从可靠性、环境影响和成本等方面比较可再生与不可再生能源。
8. Efficiency | 效率
Efficiency is a measure of how much useful energy is obtained from an energy transfer. It is usually expressed as a percentage.
效率是衡量能量转移中获得多少有用能量的指标，通常以百分比表示。
效率 (%) = (有用能量输出 ÷ 总能量输入) × 100%
J is emitted as light. The rest is wasted as heat. Its efficiency is (10 ÷ 100) × 100 = 10%.
例如，一个灯泡输入 100 J 电能，但只有 10 J 转化为光能，其余以热量形式浪费。其效率为 (10 ÷ 100) × 100 = 10%。
- Machines can reduce wasted energy through lubrication (reducing friction) and insulation (reducing heat loss).
- 机器可以通过润滑（减少摩擦）和隔热（减少热量损失）来减少浪费的能量。
- Happier energy use means less fuel consumed and lower costs.
- 提高能量使用效率意味着消耗更少的燃料和降低费用。
In biological systems, efficiency is also important. For example, only about 10% of energy is passed from one trophic level to the next in a food chain.
在生物系统中，效率也很重要。例如，在食物链中，从一个营养级到下一个营养级大约只传递 10% 的能量。
Published by TutorHao | Science Revision Series | aleveler.com
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