📚 GCSE OCR Science: Energy – Key Points | GCSE OCR 科学：能量考点精讲
Welcome to your energy topic revision for OCR GCSE Science. Energy is one of the most important concepts in physics, explaining how and why things move, heat up, and change. Understanding the key ideas – stores, transfers, calculations, and resources – will help you succeed in your exam. Let’s get started.
欢迎来到 OCR GCSE 科学能量专题复习。能量是物理学中最重要的概念之一，解释了物体如何以及为何运动、升温和变化。理解关键概念——储存、转移、计算和资源——将帮助你在考试中取得成功。现在开始吧。
1. Energy Stores and Systems | 能量储存与系统
In OCR GCSE Science, energy is stored in different forms called energy stores. The main stores you need to know are: kinetic, thermal (or internal), chemical, gravitational potential, elastic potential, electrostatic, magnetic and nuclear.
在 OCR GCSE 科学中，能量以不同形式储存，称为能量储存。你需要了解的主要储存包括：动能、热能（或内能）、化学能、重力势能、弹性势能、静电势能、磁能和核能。
A thermal energy store describes the energy a substance has due to the kinetic and potential energies of its particles. A hotter object has more thermal energy. Chemical stores hold energy in bonds between atoms, released during reactions.
热能储存描述了物质由于粒子的动能和势能而具有的能量。温度越高的物体热能越多。化学储存在原子间的化学键中，在化学反应中释放出来。
In physics, we consider a system – a single object or a group of objects. In a closed system, no energy can enter or leave, so the total energy remains constant. This makes it easier to track energy transfers.
在物理学中，我们考虑系统——单个物体或一组物体。在封闭系统中，没有能量可以进入或离开，因此总能量保持不变。这使得追踪能量转移更加容易。
2. Energy Transfers | 能量转移
Energy can be transferred between different stores through four main pathways: mechanically (by a force doing work), electrically (when a charge moves through a potential difference), by heating (due to a temperature difference), and by radiation (as waves such as light or sound).
能量可以通过四种主要途径在不同储存之间转移：机械转移（力做功）、电转移（电荷在电势差中移动）、通过加热（由于温差）以及通过辐射（如光或声波）。
For example, when you lift a book, energy is transferred mechanically from your muscles’ chemical store to the book’s gravitational potential store. When a toaster is switched on, energy is transferred electrically to the heating element’s thermal store, then by radiation to the bread.
例如，当你举起一本书时，能量从肌肉的化学储存机械地转移到书的重力势能储存。当烤面包机开启时，能量通过电流转移到加热元件的热能储存，然后通过辐射传递给面包。
It is important to describe energy transfers by naming the store from which energy is taken and the store to which it is moved, as well as the transfer pathway.
描述能量转移时，重要的是说出能量从哪个储存取出、转移到哪个储存，以及转移途径。
3. Conservation of Energy | 能量守恒
The principle of conservation of energy states that energy can be transferred, stored, or dissipated, but it can never be created or destroyed. The total energy of a closed system is always constant.
能量守恒定律指出，能量可以被转移、储存或耗散，但绝不能凭空产生或消失。封闭系统的总能量总是恒定的。
However, in most real-world processes, energy is dissipated – it spreads out into the surroundings, often as thermal energy that is no longer useful. This does not mean energy disappears; it simply becomes harder to use for doing work.
然而，在大多数现实过程中，能量会被耗散——它会散布到周围环境中，通常变成不再有用的热能。这并不意味着能量消失了；它只是变得更难以用来做功。
Understanding dissipation helps explain why perpetual motion machines are impossible and why we must carefully design machines to minimise energy waste.
理解耗散有助于解释为什么永动机不可能存在，以及为什么我们必须精心设计机器以减少能量浪费。
4. Kinetic Energy | 动能
Any moving object has kinetic energy. The amount of kinetic energy depends on its mass and speed, and is given by the equation:
任何运动的物体都具有动能。动能的大小取决于物体的质量和速度，计算公式为：
Eₖ = ½ m v²
where Eₖ is kinetic energy in joules (J), m is mass in kilograms (kg), and v is speed in metres per second (m/s).
其中 Eₖ 是动能，单位焦耳 (J)；m 是质量，单位千克 (kg)；v 是速度，单位米/秒 (m/s)。
For example, a car of mass 1000 kg travelling at 20 m/s has a kinetic energy:
Eₖ = ½ × 1000 × (20)² = 200,000 J. Doubling the speed quadruples the kinetic energy, which is why high-speed collisions are so dangerous.
例如，一辆质量为 1000 kg 的汽车以 20 m/s 的速度行驶，其动能为：
Eₖ = ½ × 1000 × (20)² = 200,000 J。速度增加一倍，动能变为原来的四倍，这就是高速碰撞非常危险的原因。
5. Gravitational Potential Energy | 重力势能
An object raised above the ground stores gravitational potential energy. The energy gained is equal to the work done against gravity, and the equation is:
物体被举高到地面上方时会储存重力势能。获得的能量等于克服重力所做的功，计算公式为：
Eₚ = m g h
where Eₚ is the gravitational potential energy in joules (J), m is mass (kg), g is the gravitational field strength (approximately 10 N/kg on Earth), and h is the height above the ground in metres (m).
其中 Eₚ 是重力势能，单位焦耳 (J)；m 是质量 (kg)；g 是重力场强度（在地球上约为 10 N/kg）；h 是离地高度，单位米 (m)。
If a 2 kg book is lifted from the floor onto a shelf 1.5 m high, it gains Eₚ = 2 × 10 × 1.5 = 30 J of gravitational potential energy. This energy can later be transferred to kinetic if the book falls.
如果一本 2 kg 的书从地板被举到 1.5 m 高的书架上，它获得了 Eₚ = 2 × 10 × 1.5 = 30 J 的重力势能。如果书掉落，这些能量可以转化为动能。
6. Elastic Potential Energy | 弹性势能
When a spring or a rubber band is stretched or compressed, it stores elastic potential energy – provided the extension is not beyond its elastic limit. The equation for a spring obeying Hooke’s law is:
当弹簧或橡皮筋被拉伸或压缩时，只要伸长量未超过其弹性限度，它就储存弹性势能。满足胡克定律的弹簧计算公式为：
Eₑ = ½ k e²
Eₑ is the elastic potential energy in joules (J), k is the spring constant in newtons per metre (N/m), and e is the extension (or compression) in metres (m). The spring constant measures how stiff the spring is.
Eₑ 是弹性势能，单位焦耳 (J)；k 是弹簧常数，单位牛/米 (N/m)；e 是伸长量（或压缩量），单位米 (m)。弹簧常数衡量弹簧的刚度。
For example, a spring with k = 40 N/m stretched by 0.2 m stores Eₑ = ½ × 40 × (0.2)² = 0.8 J. If the spring is stretched beyond its elastic limit, it will be permanently deformed and the equation no longer holds.
例如，一个 k = 40 N/m 的弹簧被拉伸 0.2 m，储存的弹性势能为 Eₑ = ½ × 40 × (0.2)² = 0.8 J。如果弹簧被拉伸超过弹性限度，它将永久变形，该公式不再适用。
7. Work Done | 做功
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, and is given by:
当一个力使物体在力的方向上移动时，力就做了功。做功的大小等于转移的能量，计算公式为：
W = F d
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).
W 是做功，单位焦耳 (J)；F 是力，单位牛 (N)；d 是沿力的方向移动的距离，单位米 (m)。
If you push a box with a constant force of 50 N over a distance of 3 m, the work done on the box is 150 J. If the force acts at a right angle to the direction of motion, no work is done by that force.
如果你用 50 N 的恒力推动一个箱子移动 3 m，对箱子做的功为 150 J。如果力的方向与运动方向垂直，则该力不做功。
For instance, when you carry a bag horizontally, the upward force you exert does no work on the bag because the motion is perpendicular to the force. All the work is done when lifting it.
例如，当你水平提着包行走时，你向上的力对包不做功，因为运动方向与力垂直。只有在向上提起包时才做功。
8. Power | 功率
Power is the rate at which energy is transferred or work is done. It tells us how quickly energy is being used. The equation for power is:
功率是能量转移或做功的速率。它告诉我们能量被使用的快慢。功率的计算公式为：
P = E / t
or using work done, P = W / t. P is power in watts (W), E is energy transferred (J), W is work done (J), and t is time in seconds (s). 1 watt equals 1 joule per second.
或用做功表示，P = W / t。P 是功率，单位瓦特 (W)；E 是转移的能量 (J)；W 是做功 (J)；t 是时间，单位秒 (s)。1 瓦特等于 1 焦耳/秒。
A motor that lifts a weight and transfers 2000 J of energy in 5 seconds has a power output of P = 2000 / 5 = 400 W. A more powerful motor can do the same work in a shorter time.
一台电动机提起重物，在 5 秒内转移了 2000 J 能量，其输出功率为 P = 2000 / 5 = 400 W。功率更大的电动机能在更短时间内完成相同的功。
9. Efficiency and Reducing Waste | 效率与减少浪费
Efficiency tells us how well a device transfers useful energy. It is calculated as the ratio of useful output energy to total input energy, often expressed as a percentage:
效率告诉我们一个设备转移有用能量的程度。它计算为有用输出能量与总输入能量之比，通常以百分比表示：
Efficiency = (useful energy output / total energy input) × 100%
No device can be 100% efficient because some energy is always dissipated, usually as thermal energy to the surroundings. The greater the proportion of useful output, the higher the efficiency.
没有设备能达到 100% 的效率，因为总有一些能量被耗散，通常是以热能形式散失到周围环境中。有用输出的比例越高，效率就越高。
We can reduce unwanted energy transfers to improve efficiency. Lubricating moving parts reduces friction and therefore thermal energy waste. Using thermal insulation, such as loft insulation or double glazing, reduces heat loss from buildings.
我们可以减少不必要的能量转移来提高效率。给运动部件加润滑剂可以减少摩擦，从而减少热能浪费。使用隔热材料，如阁楼保温层或双层玻璃，可以减少建筑物的热量损失。
In cars, aerodynamic shapes reduce air resistance and improve fuel efficiency. In electrical circuits, using thicker wires lowers resistance and reduces heating of the wires.
在汽车中，流线型设计可减少空气阻力并提高燃油效率。在电路中，使用较粗的导线可降低电阻、减少导线发热。
10. Energy Resources | 能源
Energy resources are used for electricity generation, heating and transport. They are divided into non-renewable (fossil fuels and nuclear) and renewable resources (solar, wind, hydroelectric, wave, tidal, geothermal and biofuels).
能源用于发电、供热和交通。它们分为不可再生能源（化石燃料和核能）和可再生能源（太阳能、风能、水力发电、波浪能、潮汐能、地热能和生物燃料）。
Fossil fuels – coal, oil and natural gas – are reliable and produce large amounts of energy, but they are finite and release carbon dioxide and other pollutants when burned. Nuclear power produces no CO₂, but generates radioactive waste that must be stored safely for many years.
化石燃料——煤、石油和天然气——可靠且能产生大量能量，但它们有限，燃烧时会释放二氧化碳和其他污染物。核能不产生二氧化碳，但会产生必须安全存储多年的放射性废物。
Renewable resources are replenished naturally. Wind and solar are clean but weather-dependent and cannot always
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