📚 Thermal Energy | 热能
Thermal energy is the total internal energy of an object, including the kinetic energy of its randomly moving particles and the potential energy stored in the forces between particles. Understanding thermal energy helps explain how materials heat up, cool down, change state and transfer heat between their surroundings.
热能是物体的总内能，包括其无规则运动粒子的动能以及粒子间相互作用力中储存的势能。理解热能有助于解释物质如何升温、冷却、改变状态以及在周围环境之间传递热量。
1. What is Thermal Energy? | 什么是热能？
Thermal energy is the sum of the internal energy of all particles in a substance. When a substance is heated, its particles move faster and the internal energy increases.
热能是物质中所有粒子内能的总和。当物质受热时，其粒子运动加快，内能增大。
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The unit of thermal energy is the joule (J).
热能的单位是焦耳（J）。
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Thermal energy can cause a rise in temperature or a change of state, depending on how the energy is absorbed.
热能可导致温度升高或物态变化，具体取决于能量如何被吸收。
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Temperature measures the average kinetic energy of particles, not the total thermal energy of the object.
温度量度的是粒子平均动能，而不是物体的总热能。
2. Temperature and Heat | 温度与热量
Temperature is a measure of how hot an object is, while heat is thermal energy in transit from a hotter object to a colder object. They are closely related but not the same.
温度是衡量物体有多热的量，而热量是从较热物体传向较冷物体的热能。二者关系密切但并不相同。
| Quantity / 物理量 | Description / 描述 | Unit / 单位 |
|---|---|---|
| Temperature / 温度 | Average kinetic energy of particles / 粒子平均动能 | °C or K |
| Heat energy / 热量 | Internal energy transferred between objects / 物体间转移的内能 | J |
In IGCSE Physics, always remember that heat flows naturally from a region of higher temperature to a region of lower temperature until thermal equilibrium is reached.
在IGCSE物理中，始终记住热量会自发地从高温区域流向低温区域，直到达到热平衡。
3. Conduction | 热传导
Conduction is the transfer of thermal energy through a material without any overall movement of the material itself. It is the main method of heat transfer in solids.
热传导是热量通过材料传递而不伴随材料整体运动的传热方式，是固体中主要的传热方式。
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In metals, atoms share some free electrons that can move rapidly and carry thermal energy through the metal; this makes metals good conductors.
在金属中，原子共享一些自由电子，这些电子能快速移动并在金属中携带热能，因此金属是良导体。
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Non-metals such as wood, plastic and air are poor conductors because they have very few free electrons and the particles are not closely linked.
木材、塑料和空气等非金属是热的不良导体，因为它们的自由电子很少，粒子之间联系不紧密。
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Liquids and gases are generally poor conductors of thermal energy.
液体和气体通常是热能的不良导体。
4. Convection | 热对流
Convection is the transfer of thermal energy by the movement of fluids (liquids and gases). It occurs when warmer, less dense fluid rises and cooler, denser fluid sinks to replace it.
热对流是流体（液体和气体）通过自身流动传递热能，发生在较热且密度较小的流体上升、较冷且密度较大的流体下沉补充时。
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This circulating motion is called a convection current.
这种循环运动称为对流传热环流。
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Sea breezes are caused by land and sea heating at different rates, creating convection currents in the air.
海陆风是因为陆地和海洋升温速率不同，在空气中形成对流传热环流所致。
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Hot-air balloons use the same principle: heated air expands, becomes less dense and rises.
热气球利用相同原理：加热后的空气膨胀、密度变小并上升。
5. Radiation | 热辐射
Radiation is the transfer of thermal energy by electromagnetic waves, mainly infrared radiation. It does not require a medium and can pass through a vacuum.
热辐射是通过电磁波（主要是红外线）传递热能，不需要介质，可以在真空中传播。
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Dull, black surfaces absorb and emit infrared radiation better than shiny, white surfaces.
暗淡黑色的表面比光亮白色的表面能更好地吸收和发射红外辐射。
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Highly polished surfaces reflect infrared radiation well, which is why they are used in thermos flasks.
高度抛光的表面能很好地反射红外辐射，因此用于保温瓶。
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An object at a higher temperature emits more infrared radiation than a cooler object.
温度较高的物体比温度较低的物体发射更多的红外辐射。
6. Specific Heat Capacity | 比热容
The specific heat capacity of a substance is the amount of thermal energy required to raise the temperature of 1 kg of the substance by 1 °C (or 1 K).
物质的比热容是使1kg该物质温度升高1°C（或1K）所需的热能。
ΔE = m × c × Δθ
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Where ΔE is the change in thermal energy in joules (J), m is the mass in kilograms (kg), c is the specific heat capacity in J/(kg·°C), and Δθ is the temperature change in °C.
其中ΔE是热能变化，单位为焦耳（J）；m是质量，单位为千克（kg）；c是比热容，单位为J/(kg·°C)；Δθ是温度变化，单位为°C。
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Water has a high specific heat capacity of about 4200 J/(kg·°C), so it stores a lot of thermal energy without a large temperature rise.
水的比热容约为4200 J/(kg·°C)，因此它可以吸收大量热能而温度升高不大。
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To measure specific heat capacity, an electrical heater supplies a known amount of energy to a material while the mass and temperature change are recorded, then c is calculated using the formula.
测量比热容时，用电热器向材料提供已知能量，同时记录质量和温度变化，然后利用公式计算c。
7. Latent Heat | 潜热
During a change of state, such as melting or boiling, the temperature of a substance remains constant even though thermal energy is being added or removed. This energy is called latent heat.
在熔化或沸腾等物态变化过程中，即使有热能加入或移除，物质的温度仍保持不变。这部分能量称为潜热。
E = m × L
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E is the thermal energy in joules (J), m is the mass in kilograms (kg), and L is the specific latent heat in J/kg.
E是热能，单位为焦耳（J）；m是质量，单位为千克（kg）；L是比潜热，单位为J/kg。
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Melting and boiling are endothermic processes: they absorb thermal energy. Freezing and condensing are exothermic processes: they release thermal energy.
熔化和沸腾是吸热过程：吸收热能。凝固和液化是放热过程：释放热能。
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Evaporation is different from boiling because evaporation occurs at any temperature and only at the surface of a liquid, while boiling occurs at the boiling point throughout the whole liquid.
蒸发与沸腾不同：蒸发在任何温度下都能发生，且只发生在液体表面；沸腾则在沸点下于整个液体中发生。
8. Thermal Expansion | 热膨胀
When a substance is heated, its particles gain kinetic energy and move farther apart, causing the substance to expand. As a result, the density of the substance usually decreases.
当物质受热时，粒子获得动能并彼此远离，导致物质膨胀。因此，物质的密度通常会减小。
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Solids expand the least, liquids expand more than solids, and gases expand the most.
固体膨胀最小，液体比固体膨胀更大，气体膨胀最大。
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Thermometers rely on the expansion of a liquid such as mercury or alcohol to indicate temperature.
温度计依靠汞或酒精等液体的膨胀来指示温度。
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