Energy Stores and Transfers | 能量储存与转移

📚 Energy Stores and Transfers | 能量储存与转移

Energy is a central concept in all branches of science. In IGCSE Edexcel Science, you need to understand how energy is stored, transferred, and measured, as well as how to calculate efficiency and power. This article provides a concise but complete revision guide.

能量是所有科学分支中的核心概念。在 Edexcel IGCSE 科学中，你需要理解能量如何储存、如何转移、如何测量，以及如何计算效率和功率。这篇文章提供了一个简明而完整的复习指南。

1. Energy Stores | 能量储存形式

Energy can be stored in different ways. The main energy stores are: chemical, kinetic, gravitational potential, elastic potential, thermal, magnetic, electrostatic, and nuclear.

能量可以以不同的方式储存。主要的能量储存形式包括：化学能、动能、重力势能、弹性势能、热能、磁能、静电势能和核能。

Chemical store – energy stored in bonds between atoms and molecules, e.g. food, fuels, batteries.
Kinetic store – energy possessed by a moving object.
Gravitational potential store – energy stored in an object due to its height above the ground.
Elastic potential store – energy stored when an object is stretched, compressed or twisted.
Thermal store – energy associated with the temperature of an object.
Magnetic store – energy stored in magnetic fields.
Electrostatic store – energy stored in electric fields between charged objects.
Nuclear store – energy stored in the nucleus of an atom.

You should be able to identify which energy stores are present in a simple situation, such as a moving car, a stretched spring, or a battery-powered torch.

你应该能够识别简单情境中存在哪些能量储存形式，例如一辆行驶的汽车、一根被拉伸的弹簧或一个使用电池的手电筒。

2. Energy Transfers | 能量转移方式

Energy can be transferred from one object to another, or from one store to another. There are four main ways in which energy can be transferred:

能量可以从一个物体转移到另一个物体，或从一种储存形式转移到另一种。能量转移的四种主要方式如下：

Mechanical work – a force moves an object over a distance (e.g. pushing a trolley).
Electrical work – charges move around a circuit (e.g. a fan driven by an electric motor).
Heating – energy flows from a hotter object to a colder object (e.g. a radiator warming a room).
Radiation – energy travels as electromagnetic waves (e.g. light, infrared, sound).

For example, a ball thrown upward has kinetic energy that is gradually transferred to gravitational potential energy as it rises.

例如，向上抛出的球在上升过程中，其动能逐渐转化为重力势能。

3. Conservation of Energy | 能量守恒定律

The principle of conservation of energy states that energy cannot be created or destroyed, only transferred from one store to another. The total energy before a process equals the total energy after the process.

能量守恒定律指出：能量不能被创造或消灭，只能从一种储存形式转移到另一种。过程前后的总能量保持不变。

Total energy before = Total energy after

This means that all the energy input to a system must be accounted for. In real-life systems, some energy is often transferred to the thermal store of the surroundings, which is usually considered “wasted”.

这意味着系统输入的所有能量都必须被说明去向。在现实系统中，部分能量通常会转移到周围环境的热能储存中，这通常被认为是“浪费的”能量。

4. Useful and Wasted Energy | 有用能和浪费能

In any energy transfer, we identify the useful energy as the part that is transferred to the desired store. The rest is wasted energy, which is usually transferred to the thermal store of the surroundings.

在任何能量转移中，我们将转移到预期储存形式的那部分能量称为有用能。其余部分为浪费能，通常转移到周围环境的热能储存中。

For example, in a light bulb, useful energy is light and the wasted energy is heat. In a television, useful energy is sound and light, while heat is wasted.

例如，在灯泡中，有用能是光，浪费能是热。在电视机中，有用能是声音和光，而热是浪费的。

Wasted energy is not destroyed – it spreads out and becomes harder to use. This is often linked to the idea of heating and cooling processes.

浪费能并没有被消灭——它分散开来，变得更难利用。这通常与加热和冷却过程的概念相关。

5. Efficiency | 效率

Efficiency tells us how much of the input energy is transferred to useful energy. It is a ratio, usually expressed as a percentage.

效率告诉我们输入能量中有多少被转移为有用能。它是一个比值，通常用百分比表示。

Efficiency = (Useful output energy ÷ Total input energy) × 100%

You can also use power instead of energy:

你也可以用功率代替能量：

Efficiency = (Useful output power ÷ Total input power) × 100%

No machine can be 100% efficient because some energy is always wasted, often as heat. High efficiency means less fuel or electricity is wasted.

没有任何机器能达到 100% 的效率，因为总有一些能量会被浪费，通常是以热的形式。高效率意味着更少的燃料或电能被浪费。

6. Power | 功率

Power is the rate at which energy is transferred or the rate at which work is done. It is measured in watts (W), where 1 W = 1 joule per second.

功率是能量转移的速率或做功的快慢。它用瓦特（W）来衡量，其中 1 W = 1 焦耳每秒。

Power (W) = Energy transferred (J) ÷ Time taken (s)

Another useful equation is:

另一个有用的公式是：

Power (W) = Work done (J) ÷ Time taken (s)

For example, a 60 W light bulb transfers 60 joules of energy every second.

例如，一个 60 W 的灯泡每秒转移 60 焦耳的能量。

7. Kinetic and Potential Energy | 动能与势能

Two key equations you must memorise for IGCSE Science are for kinetic energy and gravitational potential energy.

你需要记住的两个关键方程是动能方程和重力势能方程。

Kinetic energy (EK):

EK = ½ × m × v²

where m is mass in kilograms (kg), v is speed in metres per second (m/s), and EK is in joules (J).

其中 m 是质量（千克），v 是速度（米/秒），EK 的单位是焦耳。

Gravitational potential energy (EP):

EP = m × g × h

where m is mass (kg), g is gravitational field strength (9.8 N/kg on Earth), and h is height in metres (m).

其中 m 是质量（千克），g 是重力场强度（地球上为 9.8 N/kg），h 是高度（米）。

These equations are often used together, for example when an object falls and its gravitational potential energy is converted to kinetic energy.

这些方程经常一起使用，例如当物体下落时，其重力势能转化为动能。

8. Energy Resources | 能源资源

On a larger scale, we need energy resources to generate electricity, transport and heating. These are divided into renewable and non-renewable resources.

在大规模层面上，我们需要能源资源来发电、运输和供暖。这些资源分为可再生能源和不可再生能源。

Non-renewable	Renewable
Coal, oil, natural gas, nuclear fuels	Solar, wind, hydroelectric, geothermal, biomass, tidal, wave

Non-renewable resources are finite and release carbon dioxide when burned, contributing to climate change. Renewable resources are replenished naturally but may be unreliable or have high initial costs.

不可再生资源是有限的，燃烧时会释放二氧化碳，导致气候变化。可再生资源可以自然补充，但可能不稳定或初始成本较高。

9. Applying Energy Calculations | 能量计算应用

In exams, you may be asked to calculate efficiency, power, kinetic energy, or gravitational potential energy. Always show your working and include units.

在考试中，你可能需要计算效率、功率、动能或重力势能。务必写出计算过程并包含单位。

Example: A 4 kg object is moving at 3 m/s. Calculate its kinetic energy.

示例：一个 4 kg 的物体以 3 m/s 的速度运动。计算其动能。

EK = ½ × 4 × 3² = ½ × 4 × 9 = 18 J

Another example: A motor lifts a box of mass 10 kg to a height of 2 m. If g = 10 N/kg, how much gravitational potential energy does it gain?

另一个例子：一个电动机将质量为 10 kg 的箱子提升到 2 m 的高度。如果 g = 10 N/kg，它获得了多少重力势能？

EP = 10 × 10 × 2 = 200 J

Remember to convert units where necessary: 1 kJ = 1000 J, 1 MJ = 1,000,000 J, 1 kW = 1000 W.

记住在必要时进行单位换算：1 kJ = 1000 J，1 MJ = 1,000,000 J，1 kW = 1000 W。

10. Common Misconceptions | 常见误区

Students often make mistakes with energy topics. Here are some points to remember:

学生经常在能量主题上犯错。以下是一些需要记住的点：

Energy is not a force – it cannot be “used up” in the sense of disappearing, but it can become less useful as it spreads out.
Energy is not the same as power – power measures how fast energy is transferred.
In a closed system, energy is conserved, but the “useful” energy decreases because of wasted heat.
Gravitational potential energy depends on height relative to a reference level (often the ground).
Kinetic energy depends on the square of speed, so if speed doubles, kinetic energy quadruples.

Understanding these ideas will help you avoid common exam traps and apply equations correctly.

理解这些概念将帮助你避免常见的考试陷阱，并正确应用公式。

Published by TutorHao | Science Revision Series | aleveler.com

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Energy Stores and Transfers | 能量储存与转移