章节大纲

  • Sunlight streaming through a window illuminates dust particles floating in the air.

    Rays of sunlight pour into this old room and reflect off dust particles in the air. Did you ever see dust particles in the air like these? If so, you may have noticed that they constantly move about at random.
    ::阳光照耀的光线涌进这个旧房间,反射空气中的尘埃粒子。你曾经见过这样的尘埃粒子吗?如果是这样的话,你可能已经注意到它们经常随机移动。

    Q : Why do dust particles move randomly in the air?
    ::问题:为什么尘埃粒子在空气中随机移动?

    A : Invisible particles of in the air are constantly moving and bumping into them.
    ::A:空气中的隐形微粒不断移动并撞上它们。

    Launch the simulation below to help you visualize the invisible particles that make up the air:
    ::启动下面的模拟 帮助您视觉化 组成空气的隐形粒子:

    Pressure of Gas Particles
    ::气粒气压

    Because gas particles in the air—like particles of all fluids—are constantly moving and bumping into things, they exert pressure . The pressure exerted by the air in the atmosphere is greater close to Earth’s surface and decreases as you go higher above the surface. You can see this in the Figure .
    ::因为空气中的气体粒子——所有液体中的气体粒子——不断移动和撞入事物,它们施加压力。空气在大气中施加的压力更接近地球表面,随着地球表面的上升而下降。您可以从图中看到这一点。

    Graph showing the relationship between altitude and atmospheric pressure, highlighting Mount Everest.

    Q : Denver, Colorado, is called the “mile-high city” because it is located 1 mile (1.6 km) above sea level. What is the average atmospheric pressure that high above sea level?
    ::问题:科罗拉多州丹佛被称为“里高城市 ” , 因为它位于海平面1英里(1.6公里)以上。 海平面高的平均大气压力是什么?

    A : From the Figure , the average atmospheric pressure 1.6 km above sea level is about 85 kPa.
    ::A:从图中可以看出,海拔1.6公里以上的平均大气压力约为85千帕。

    Explaining Changes in Air Pressure with Altitude
    ::解释高空空气压力变化

    There are two reasons why air pressure decreases as altitude increases: density and depth of the atmosphere.
    ::随着高度升高,空气压力下降有两个原因:大气密度和深度。

    • Most gas molecules in the atmosphere are pulled close to Earth’s surface by gravity, so gas particles are denser near the surface. With more gas particles in a given volume , there are more collisions of particles and therefore greater pressure.
      ::大气中大多数气体分子都是通过引力拉近地球表面的,因此气体粒子在表面附近密度更高。 气体粒子在一定量内增加,粒子碰撞更多,因此压力更大。
    • The depth ( from top to bottom) of the atmosphere is greatest at sea level and decreases at higher altitudes. With greater depth of the atmosphere, more air is pressing down from above. Therefore, air pressure is greatest at sea level and falls with increasing altitude. On top of Mount Everest, which is the tallest mountain on Earth, air pressure is only about one-third of the pressure at sea level.
      ::大气的深度( 从上到下)在海平面上最大,在高海拔时降幅最大。随着大气深度的提高,更多的空气从上往下压。因此,大气压力在海平面上最大,并随着海平面的升高而下降。 在地表最高的珠穆朗玛峰顶端,空气压力只占海平面压力的三分之一左右。

    How We Use Air Pressure
    ::我们如何使用空气压力

    The pressure of air in the atmosphere allows us to do many things, from sipping through a straw to simply breathing. You can see in the Figures and how we use air pressure in both of these ways.
    ::大气中的空气压力让我们可以做很多事情,从吸水到吸草到简单的呼吸。你可以从数字中看到,以及我们如何用这两种方式使用气压。

    A child drinks from a straw while leaning over a glass of milk.

    When you first suck on a straw, you remove air from the straw, so the air pressure in the straw is lower that the air pressure on the surface of the drink. A fluid always flows from an area of higher pressure to an area of lower pressure, so the drink moves up the straw and into your mouth.
    ::当你第一次吸食稻草时,你从稻草中除去空气,所以稻草中的空气压力要小于饮料表面的空气压力。液体总是从高压地区流到低压地区,这样饮料就会从吸草上移到你的嘴里。

    Human respiration showing diaphragm movement and airflow during breathing.

     

    Summary
    ::摘要

    • The pressure exerted by the air in the atmosphere is greatest at Earth’s surface and falls as altitude increases. The reason is that density and depth of the atmosphere are greatest at sea level and decline with increasing altitude.
      ::空气在大气中施加的压力在地球表面是最大的,随着高度升高而下降。 原因是大气的密度和深度在海平面上最大,随着高度升高而下降。
    • The pressure of air in the atmosphere allows us to do many things, from sipping through a straw to breathing.
      ::大气中的空气压力 使我们能够做很多事情, 从吸食到吸管到呼吸。

    Review
    ::回顾

    1. Describe how air pressure in the atmosphere changes from sea level to the top of the atmosphere.
      ::描述大气中的气压如何从海平面向大气顶端变化。
    2. What factors explain why atmospheric pressure changes as altitude increases?
      ::是什么因素解释高度升高导致大气压力变化的原因?
    3. Explain how differences in air pressure allow us to breathe.
      ::解释空气压力的差异 如何让我们呼吸。