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OxfordAQA · International GCSE · Physics Topik 4 4:11 Narasi bahasa Inggris · Subtitle bahasa Inggris + 中文 disematkan langsung
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Everything is made of particles.
一切物质都由粒子构成。
In a solid they are fixed in place and touching.
在固体中，粒子固定不动、彼此接触。
In a liquid they still touch, but move past each other at random.
在液体中，粒子仍然接触，但随机地相互滑过。
In a gas they are far apart and move fast.
在气体中，粒子相距很远，运动很快。
Their energy and spacing explain heating, cooling and expansion.
粒子的能量和间距解释了加热、冷却和热膨胀。
Specific heat capacity, c, is the energy needed to raise one kilogram of a substance by one degree Celsius.
比热容 c 是使 1 千克物质升高 1 摄氏度所需的能量。
The energy is m times c times the temperature change.
能量等于 m 乘以 c 乘以温度变化。
Heating 1.5 kilograms of water, c 4200, by 40 degrees takes 1.5 times 4200 times 40: 252 000 joules.
把 1.5 千克的水（c 为 4200）加热 40 度，需要 1.5 乘 4200 乘 40，即 252 000 焦耳。
A 50 watt heater warms a 2.0 kilogram aluminium block for 600 seconds, and its temperature rises by 15 degrees.
一个 50 瓦的加热器给 2.0 千克的铝块加热 600 秒，温度升高 15 度。
Energy in is 50 times 600, 30 000 joules, so c is 30 000 divided by 2.0 times 15: 1000.
输入能量为 50 乘 600，即 30 000 焦耳，所以 c 等于 30 000 除以 2.0 乘 15，即 1000。
The accepted value is about 900.
公认值约为 900。
Some energy heated the air, so the measured value is too high.
部分能量加热了空气，所以测量值偏高。
A cooling curve for stearic acid.
硬脂酸的冷却曲线。
The liquid cools, until at its freezing point the temperature stays flat.
液体先降温，到凝固点时温度保持不变。
The substance is not doing nothing: it is freezing, and releasing latent heat as fast as energy is removed.
这时物质并不是什么都没做：它正在凝固，释放潜热的速度与被带走能量的速度相同。
Once it is all solid, the solid cools again.
全部变成固体后，固体再继续降温。
To turn 0.10 kilograms of ice at 0 degrees into water at 20 degrees takes two stages.
把 0.10 千克 0 度的冰变成 20 度的水，要分两步。
Melting at 0 degrees: 0.10 times 334 000, 33 400 joules.
先在 0 度熔化：0.10 乘 334 000，即 33 400 焦耳。
Then warming the water: 0.10 times 4200 times 20, 8400 joules.
再加热水：0.10 乘 4200 乘 20，即 8400 焦耳。
The total is 41 800 joules; the melting needs four times more.
共 41 800 焦耳；熔化所需的能量是加热的四倍。
Conduction passes energy along a solid by particle vibration: the hot end's particles vibrate harder and jostle their neighbours.
热传导通过粒子振动沿固体传递能量：热端的粒子振动更剧烈，撞击相邻粒子。
In metals, free electrons carry energy quickly through the whole piece, which is why metals are good conductors.
在金属中，自由电子把能量迅速带到整块金属，所以金属是良导体。
Convection circulates a fluid.
对流使流体循环。
Near the heater the particles gain energy and move apart, so that fluid becomes less dense and rises.
加热器附近的粒子获得能量、彼此分开，这部分流体密度变小而上升。
At the top it spreads out and cools, and the cooler fluid sinks to take its place: a convection current.
到了上方，它向两边散开并冷却，较冷的流体下沉补充：这就是对流。
Evaporation turns the fastest surface molecules into vapour, so the liquid left behind is cooler.
蒸发使表面最快的分子变成蒸气，所以剩下的液体变冷。
It is faster at a higher temperature, with a larger surface area, with a draught over the surface, and in lower humidity.
温度越高、表面积越大、表面有风、湿度越低，蒸发越快。
The rate of energy transfer by heating grows with surface area and with the temperature difference.
通过加热转移能量的速率随表面积和温差增大而增大。
Cooling fins on an engine or a computer chip maximise the area.
发动机或电脑芯片上的散热片使面积最大化。
Animals show the same design: in hot climates large ears lose heat; in cold climates small ears keep it.
动物也有同样的“设计”：炎热地区的动物耳朵大，便于散热；寒冷地区的动物耳朵小，便于保温。
Most substances expand when heated.
大多数物质受热膨胀。
That is a hazard for bridges and roofs, which need gaps and rollers.
这对桥梁和屋顶是隐患，需要留缝隙、装滚轴。
It is also useful: a bimetallic strip is two metals joined.
它也有用处：双金属片由两种金属贴合而成。
When heated, the brass expands more than the steel, so the strip bends and breaks a circuit: a thermostat.
受热时黄铜比钢膨胀得多，所以金属片弯曲，断开电路：这就是恒温器。
Four common mistakes. Using the final temperature instead of the change. Using m c delta theta while a substance melts or boils, when the temperature is not changing. Reading the flat part of a cooling curve as nothing happening. And saying heat rises: hot fluid rises, because it is less dense.
四个常见错误：用最终温度代替温度变化；在物质熔化或沸腾、温度不变时还用 m c Δθ；把冷却曲线的平坦部分当作什么都没发生；以及说“热往上升”：上升的是热的流体，因为它密度更小。
Check yourself.
自我检测。
Heating 2 kilograms of aluminium, c 900, by 30 degrees takes 54 000 joules.
把 2 千克铝（c 为 900）加热 30 度需要 54 000 焦耳。
Melting 0.5 kilograms with a latent heat of 330 000 joules per kilogram takes 165 000 joules.
熔化 0.5 千克、熔化热为每千克 330 000 焦耳的物质需要 165 000 焦耳。
Warm water rises because it is less dense; fins have a large area to transfer energy faster.
温水上升是因为密度更小；散热片面积大是为了更快地转移能量。