最新评论 (0)


Describing the invisible properties of gas - Brian Bennett

每一天 每一分 每一秒 我们都在呼吸
Every minute of every day,
you breathe without even thinking about it.
从呱呱坠地到垂暮老死 你的身体都在自发地做着这件事
Your body does it on its own, from the day you’re born until the day you die.
横膈肌收缩 为身体注入氧气
You have muscles contract to bring oxygen, a gas,
氧气进入肺里 然后经毛细血管进入血液循环 最后被输送到你身体的每个细胞
into your lungs, which is then transferred by your bloodstream to every cell in your body.
Gases are strange.
它看不见摸不着 但我们却能感知到它们的存在
We can’t see them, but we know they’re there because we can feel them.
我们感知到的所谓的“呼吸” 其实是亿万空气分子涌进体内
What we experience as wind is really trillions and trillions of gas molecules slamming into your body.
还挺舒服的 对吧?
And it feels good, right?
Science is based on observation.
然而 空气分子实在是太小了 我们并不能直接用肉眼观察到
Unfortunately, we cannot observe gases with our eyes — they’re too small.
我们只好用其他感官来感知 并得出结论
We have to use our other senses to make observations and draw conclusions.
所有观察到的数据被汇总编集之后 我们建立起了一个模型
Observations are then compiled, and we create a model.
No, not that kind of model.
A model is a way scientists describe the properties of physical phenomena.
First, gases always move in a straight line.
我们没办法演示这个运动 因为重力总是会把东西往下拉
We don’t really have anything to demonstrate this with because gravity always pulls objects down.
因此 不妨想象一下出膛的子弹 以恒定的速度作直线运动
So imagine a bullet fired from a gun, and that bullet goes on at a constant speed in a perfectly straight line.
That would be like a gas molecule.
其次 空气分子实在是太小 小到它们本身不占任何体积
Second, gases are so small, they occupy no volume on their own.
但当它们聚为整体时 比如给气球充气 你就能看到它们体积的变化了
As a group they do, blow up any balloon and you can see how that volume changes.
但是 相较于其他物体 单独的空气是没有体积的
But single gases have no volume compared to other forms of matter.
比起度量这么小的东西 我们还不如简单的把它归零
Rather than calculating such a small amount of matter, we just call it zero for simplicity.
第三 如果空气分子间发生碰撞——它们确实这样——记住,这只是个假设
Third, if gas molecules collide, and they do — remember, these are assumptions —
their energy remains constant.
简单地说 就像在一个足球上放一个网球 然后把足球往下扔
An easy way to demonstrate this is by dropping a soccer ball with a tennis ball balanced on top.
足球因为体积大 因此它的重力势能更大
Because the soccer ball is bigger, it has more potential energy,
and the energy from the larger ball is transferred to the smaller tennis ball
能量转移后 小一点的网球就会弹走
and it flies away when that energy is transferred.
此时 总动能守恒
The total energy stays the same.
Gases work the same way.
当它们发生碰撞时 小的气体微粒会加速 而大的则会减速
If they collide, smaller particles will speed up, larger particles will slow down.
The total energy is constant.
第四 空气不会相互吸引 它们并不喜欢接触
Fourth, gases do not attract one another, and they don’t like to touch.
还记得第三条吗? 实际上 它们会相互碰撞
But remember rule three. In reality, they do collide.
最终 气体携带的能量与温度是成正比的
Finally, gases have energy that is proportional to the temperature.
温度越高 气体所携带的能量越大
The higher the temperature, the higher the energy the gases have.
最神奇的是 在温度相同的情况下 所有气体携带的能量一致
The crazy thing is that at the same temperature, all gases have the same energy.
这并不取决于它的种类 而仅取决于它的温度
It doesn’t depend on the type of gas, just the temperature that gas is at.
时刻记住 这是个基于我们观察而构建的模型 它用来研究气体粒子的运动
Keep in mind this is a model for the way gas particles behave, and based on our observations,
gases always move in straight lines.
它们太小了 小到无法衡量
They’re so small, that they’re not measurable on their own,
and they don’t interact with one another.
可一旦气体粒子间发生碰撞 就必然伴有能量的转移
But if they do bump into one another, that energy is transferred from one particle to another,
并且 总的能量保持不变
and the total amount never changes.
温度才是主要的影响因素 实际上 处于同一温度下的气体粒子 总是具有相同的平均能量
Temperature has a major effect, and in fact,
咻~ 让我喘口气歇歇
all gases at the same temperature have the same average energy.Whew! I need to go catch my breath.