📚 IB CCEA Science: Energy Revision Notes | IB CCEA 科学：能量 考点精讲
Energy is a core concept in IB and CCEA science syllabi. It describes the capacity to do work and exists in many forms, from kinetic to thermal. Understanding energy transformations and conservation is essential for explaining phenomena from molecular collisions to global power generation.
能量是IB和CCEA科学课程的核心概念。它描述了做功的能力，并以多种形式存在，从动能到内能。理解能量的转化与守恒对于解释从分子碰撞到全球发电等现象至关重要。
1. What is Energy? | 能量是什么？
In physics, energy is defined as the ability to do work. Work is done when a force moves an object through a distance in the direction of the force. Energy is a scalar quantity, meaning it has magnitude but no direction.
在物理学中，能量被定义为做功的能力。当力使物体沿力的方向移动一段距离时，就做了功。能量是标量，即它有大小但没有方向。
The SI unit of energy is the joule (J). One joule equals the work done by a force of one newton moving an object one metre.
能量的国际单位是焦耳（J）。1焦耳等于1牛顿的力使物体移动1米所做的功。
2. Forms of Energy | 能量的形式
Energy can be stored in different ways and is often classified into forms: kinetic, gravitational potential, elastic potential, thermal (internal), chemical, nuclear, electromagnetic, and sound energy.
能量可以以不同方式储存，通常分为以下形式：动能、重力势能、弹性势能、内能（热能）、化学能、核能、电磁能和声能。
Kinetic energy is associated with moving objects, while potential energies are stored due to position or condition. Thermal energy is related to the random motion of particles.
动能与运动的物体有关，而势能则因位置或状态而储存。内能则与粒子的随机运动有关。
3. Work and the Work-Energy Principle | 功与功能原理
Work (W) is done when a force (F) causes displacement (d) in the direction of the force: W = F × d. If the force and displacement are at an angle θ, then W = F d cos θ.
当力（F）使物体沿力的方向发生位移（d）时，就做了功（W）：W = F × d。如果力与位移成角度θ，则 W = F d cos θ。
W = F × d or W = F d cos θ
The work-energy principle states that the net work done on an object equals its change in kinetic energy. This links the concept of work directly to energy transfer.
功能原理指出，对物体所做的净功等于其动能的变化。这直接将功与能量传递联系起来。
4. Kinetic Energy | 动能
Kinetic energy (KE) is the energy an object has due to its motion. It depends on mass (m) and speed (v). The equation is KE = ½ m v².
动能（KE）是物体由于运动而具有的能量。它取决于物体的质量（m）和速率（v）。公式为 KE = ½ m v²。
KE = ½ m v²
For example, a car of mass 1000 kg moving at 20 m/s has KE = 0.5 × 1000 × (20)² = 200,000 J. Doubling the speed quadruples the kinetic energy.
例如，一辆质量为1000 kg的汽车以20 m/s行驶，其动能 KE = 0.5 × 1000 × (20)² = 200000 J。速率加倍，动能将变为原来的四倍。
5. Gravitational Potential Energy | 重力势能
Gravitational potential energy (GPE) is stored by an object raised above the ground. It is given by: ΔEₚ = m g Δh, where g is the gravitational field strength (≈ 9.8 N/kg on Earth).
重力势能（GPE）是物体因被举高而储存的能量。公式为：ΔEₚ = m g Δh，其中g是重力场强度（地球表面约9.8 N/kg）。
ΔEₚ = m g Δh
When an object falls, gravitational potential energy is converted into kinetic energy, assuming negligible air resistance. At the highest point, KE is minimum; at the lowest, GPE is minimum.
物体下落时，重力势能转化为动能（忽略空气阻力）。在最高点，动能最小；在最低点，重力势能最小。
6. 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 or transformed from one form to another. The total energy in a closed system remains constant.
能量守恒定律指出，能量不能被创造或消灭，只能从一种形式传递或转化为另一种形式。一个封闭系统中的总能量保持不变。
In a pendulum swinging, GPE at the highest point converts to KE at the lowest, then back to GPE. Though some energy dissipates as heat due to air resistance, the total energy is still conserved.
在摆动的摆锤中，最高点的重力势能转化为最低点的动能，再转回重力势能。尽管一部分能量因空气阻力而耗散为热，但总能量仍然守恒。
7. Energy Transfers and Transformations | 能量传递与转化
Energy can be transferred between stores via four principal pathways: mechanically (by a force doing work), electrically (by an electric current), by heating (due to temperature difference), and by radiation (light or sound waves).
能量可通过四种主要途径在储存库之间传递：通过机械方式（力做功）、电方式（电流）、加热方式（温差引起）和辐射方式（光波或声波）。
In a light bulb, electrical energy is transferred into light and thermal energy. In a battery-powered car, chemical energy becomes electrical energy, then kinetic energy.
在灯泡中，电能转化为光能和内能；在电池驱动的汽车中，化学能转化为电能，再转化为动能。
8. Power | 功率
Power is the rate at which energy is transferred or work is done. It is calculated as P = E / t or P = W / t, where E is energy transferred and t is time taken.
功率是能量传递或做功的速率。计算公式为 P = E / t 或 P = W / t，其中E是传递的能量，t是所用时间。
P = E / t
The SI unit of power is the watt (W). One watt equals one joule per second. A high-power appliance transfers energy more quickly.
功率的国际单位是瓦特（W）。1瓦特等于1焦耳每秒。高功率的电器传递能量更快。
9. Efficiency | 效率
Efficiency measures how much of the input energy is usefully transferred. It can be expressed as a percentage using: Efficiency = (useful output energy / total input energy) × 100%.
效率衡量输入能量中有多少被有用地传递。可以用百分比表示：效率 =（有用输出能量 / 总输入能量）× 100%。
η = (Euseful / Einput) × 100%
In practical systems, some energy is always dissipated as thermal energy to the surroundings, so efficiency is always less than 100%. Energy-saving devices aim to reduce these losses.
在实际系统中，总有一部分能量以热能形式耗散到周围环境中，因此效率始终低于100%。节能设备旨在减少这些损失。
10. Thermal Energy and Heat Transfer | 内能与热传递
Thermal energy is the total kinetic and potential energy of particles within a substance. Heat transfer occurs via conduction, convection, and radiation.
内能是物质内部粒子的动能和势能总和。热传递通过传导、对流和辐射进行。
Conduction involves vibrations passing along a material or free electrons colliding in metals. Convection occurs in fluids due to density differences caused by heating. Radiation transfers energy by electromagnetic waves and does not require a medium.
传导涉及粒子振动在材料中传递或金属中自由电子的碰撞。对流因加热引起的密度差异在流体中发生。辐射通过电磁波传递能量，不需要介质。
11. Energy Resources | 能源
Energy resources are used to generate electricity or provide heating and transport. They are classified as non-renewable (fossil fuels, nuclear) and renewable (solar, wind, hydro, tidal, geothermal, biomass).
能源用来发电、供暖和运输。它们分为不可再生能源（化石燃料、核能）和可再生能源（太阳能、风能、水能、潮汐能、地热能、生物质能）。
| Resource | 能源 | Advantages | 优点 | Disadvantages | 缺点 |
|---|---|---|
| Fossil Fuels | 化石燃料 | Reliable, high energy density | CO₂ emissions, finite |
| Nuclear | 核能 | No CO₂, high output | Radioactive waste, safety risks |
| Solar | 太阳能 | Clean, abundant | Intermittent, requires large area |
| Wind | 风能 | Renewable, low running costs | Noise, visual impact, variable |
Selecting an energy resource involves balancing environmental impact, cost, reliability, and energy output. Many countries use a mix to ensure energy security.
选择能源需要平衡环境影响、成本、可靠性和能量输出。许多国家采用能源组合以确保能源安全。
12. Sankey Diagrams and Energy Analysis | 桑基图与能量分析
Sankey diagrams show energy transfers using arrows. The width of each arrow is proportional to the amount of energy it represents. Useful energy output is shown as an arrow continuing forward, while wasted energy branches downward.
桑基图用箭头展示能量传递。每个箭头的宽度与它所代表的能量成正比。有用能量输出显示为继续向前的箭头，而浪费的能量则向下分支。
They make it easy to visualise efficiency. For a light bulb, a thick input arrow (electrical energy) splits into a thin useful light arrow and a thick wasted heat arrow. Efficiency can be deduced from the relative widths.
桑基图便于直观判断效率。对于灯泡，粗的输入箭头（电能）分裂为细的有用光箭头和粗的浪费热箭头。可从相对宽度推断效率。
Published by TutorHao | Science Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导