Section outline

  • General

    Collapse all Expand all

  • 轨道运动

    Comparison of Earth’s size to the massive sun, highlighting orbital motion and gravity.

    As you can see in this NASA photo, Earth is tiny compared with the massive sun. The sun’s gravity is relatively strong because the force of gravity between two objects is directly proportional to their masses. Gravity between the sun and Earth pulls Earth toward the sun, but Earth never falls into the sun. Instead, it constantly revolves around the sun, making one complete revolution every 365 days.
    ::正如你们从美国航天局的这张照片中可以看到的,地球与巨大的太阳相比是很小的。太阳的引力相对较强,因为两个天体之间的引力与其质量成正比。太阳和地球之间的引力将地球引向太阳,但地球从未掉入太阳。 相反,它不断围绕太阳旋转,每365天就进行一次彻底的革命。

    Q : Why doesn’t the sun’s gravity pull Earth down to the surface of the sun?
    ::问:为什么太阳的引力不把地球拖下太阳表面?

    A : Earth has enough forward to partly counter the force of the sun’s gravity.
    ::答:地球有足够的前进力来部分对抗太阳引力。

    What Is Orbital Motion?
    ::什么是轨道运动?

    Earth and many other bodies—including asteroids, comets, and the other planets—move around the sun in curved paths called orbits. Generally, the orbits are elliptical, or oval, in shape. You can see the shape of Earth’s orbit in the Figure . Because of the sun’s relatively strong gravity, Earth and the other bodies constantly fall toward the sun, but they stay far enough away from the sun because of their forward velocity to fall around the sun instead of into it. As a result, they keep orbiting the sun and never crash to its surface. The motion of Earth and the other bodies around the sun is called orbital motion . Orbital motion occurs whenever an object is moving forward and at the same time is pulled by gravity toward another object. 
    ::地球和许多其他物体 — — 包括小行星、彗星和其他行星 — — 都以称为轨道的曲线轨道绕着太阳绕过太阳。 一般来说,轨道的形状是椭圆形的,或是奥瓦尔形的。 你可以在图中看到地球轨道的形状。 由于太阳相对强大的引力,地球和其他物体不断向太阳倾斜,但它们离太阳足够远,因为它们的前向速度会落在太阳周围而不是太阳里面。因此,它们一直绕着太阳绕着太阳绕着太阳,而不会坠落到它的表面。地球和太阳周围的其他物体的运动被称为轨道运动。当一个物体向前移动时,轨道运动就会发生,同时由引力拉向另一个物体。

    Elliptical orbits of Earth and other bodies around the sun.

    Orbital Motion of the Moon
    ::月球轨道运动

    Just as Earth orbits the sun, the moon also orbits Earth. The moon is affected by Earth’s gravity more than it is by the gravity of the sun because the moon is much closer to Earth. The gravity between Earth and the moon pulls the moon toward Earth. At the same time, the moon has forward velocity that partly counters the force of Earth’s gravity. So the moon orbits Earth instead of falling down to the surface of the planet.
    ::正如地球环绕太阳,月亮也环绕地球。月球受到地球引力的影响大于太阳引力的影响,因为月球离地球更近。地球和月球之间的引力将月球引向地球。与此同时,月球的前进速度部分地抵消了地球引力。因此月球绕地球轨道,而不是坠落到地球表面。

    The Figure shows the forces involved in the moon’s orbital motion around Earth. In the diagram, v represents the forward velocity of the moon, and a represents the due to gravity between Earth and the moon. The line encircling Earth shows the moon’s actual orbit, which results from the combination of v and a. 
    ::图中显示了月球轨道运动在地球周围的力量。 在图表中, v 代表月球的前进速度,并代表了地球和月球之间的引力。 环绕地球的线显示的是月球的实际轨道,这是V和a的结合结果。

    The moon's orbit around Earth, showing forces and speeds involved.

    Watch the video below to learn more about the orbital motion of the moon around the Earth:
    ::观看下面的视频, 以了解更多关于月球绕地球轨道运动的信息:

    Satellites also orbit planets in a circular pattern due to the force of gravity. Launch the PLIX Interactive below to explore how satellites stay in orbit:
    ::由于重力,卫星还以循环模式运行行星。

    Summary
    ::摘要

    • Orbital motion occurs whenever an object is moving forward and at the same time is pulled by gravity toward another object.
      ::当一个物体向前移动,同时被引力拉向另一个物体时,轨道运动即发生。
    • The forward velocity of the object combines with acceleration due to gravity toward the other object. The result is a circular or oval path called an orbit, in which one object keeps moving around the other.
      ::物体的前方速度与因引力而加速到另一个物体的加速程度相结合。结果是一个圆形或奥瓦尔路径,称为轨道,其中一个物体一直绕着另一个物体移动。
    • Because of the relatively great gravity of the sun, Earth orbits the sun. The moon orbits Earth rather than the sun because it is much closer to Earth.
      ::由于太阳的引力相对较大,地球环绕太阳运行,月亮绕着地球而不是太阳运行,因为它离地球更近。

    Review
    ::回顾

    1. Define orbit and orbital motion, and explain why orbital motion occurs.
      ::界定轨道和轨道运动,并解释为何发生轨道运动。
    2. In addition to the moon, artificial satellites also orbit Earth. What factors do you think must be taken into account to ensure that a satellite keeps orbiting Earth rather than falling back to Earth’s surface?
      ::除了月球之外,人造卫星还绕着地球轨道运行。 你认为需要考虑哪些因素来确保卫星保持地球轨道,而不是返回地球表面?
    3. Earth is closer to nearby planets including Venus and Mars than it is to the sun. Why don’t these other planets pull Earth toward them and cause it to veer off its orbit around the sun.
      ::地球比太阳更接近包括金星和火星在内的邻近行星。 为何这些其他行星不将地球引向它们,使其脱离太阳周围的轨道。