章节大纲

  • Portrait of Isaac Newton, a key figure in the study of gravity.

    You may have heard a story about Isaac Newton coming up with the idea of gravity when an apple fell out of a tree and hit him in the head. The story isn’t true, but seeing how things like apples fall to Earth helped Newton form his ideas about gravity, the force of attraction between things that have mass. Of course, people had known about the effects of gravity for thousands of years before Newton came along. After all, they constantly experienced gravity in their daily lives. They observed over and over again that things always fall toward the ground. However, it wasn’t until Newton developed his law of gravity in the late 1600s that people knew gravity applies to everything in the universe that has mass.
    ::你可能听说过一个故事,关于Isaac Newton在苹果从树上掉下来击中他头部时带着重力概念出现的故事。 故事不是真的,但看到苹果掉到地球时如何帮助牛顿形成了他关于重力的观念,即大量事物之间的吸引力。 当然,人们在牛顿出现之前数千年就已经知道重力的影响。 毕竟,他们在日常生活中不断经历重力。他们一再观察到,事情总是落在地上。 然而,直到牛顿在1600年代后期制定了他的重力法则,人们才知道重力适用于有重力的宇宙。

    Newton’s Law of Universal Gravitation
    ::牛顿的万国引力法

    Newton was the first to suggest that gravity is universal and affects all objects in the universe. That’s why Newton’s law of gravity is called the law of universal gravitation . Universal gravitation means that the force that causes an apple to fall from a tree to the ground is the same force that causes the moon to keep moving around Earth. Universal gravitation also means that while Earth exerts a pull on you, you exert a pull on Earth. In fact, there is gravity between you and every mass around you—your desk, your book, your pen. Even tiny molecules of are attracted to one another by the force of gravity. 
    ::牛顿首先提出引力是普遍性的,它影响到宇宙中的所有物体。这就是为什么牛顿的引力定律被称为普遍引力定律的原因。 普遍引力意味着导致苹果从一棵树落到地上的力与导致月球环绕地球移动的力相同。 普遍引力还意味着当地球对你们拉动时,你会对地球拉动。 事实上,你和你的周围的每个质量——你的桌子、书本、笔——之间都有引力。 甚至连微小的分子也会被重力吸引到对方身上。

    Q : Newton’s law of universal gravitation had a huge impact on how people thought about the universe. Why do you think it was so important?
    ::问题:牛顿的普遍引力定律对人们如何看待宇宙产生了巨大影响。 为什么你认为宇宙如此重要?

    A : Newton’s law was the first that applied to the entire universe. It explains the motion of objects not only on Earth but in outer space as well.
    ::A:牛顿的法律是第一个适用于整个宇宙的法律,它解释了物体不仅在地球上,而且在外层空间的移动。

     

     

     

    Factors That Influence the Strength of Gravity
    ::影响重力强度的因素

    Newton’s law also states that the strength of gravity between any two objects depends on two factors: the masses of the objects and the between them.
    ::牛顿法律还规定,两个物体之间的重力取决于两个因素:物体的重量和物体之间的重力。

    • Objects with greater mass have a stronger force of gravity between them. For example, because Earth is so massive, it attracts you and your desk more strongly than you and your desk attract each other. That’s why you and the desk remain in place on the floor rather than moving toward one another.
      ::质量较大的物体在它们之间具有更大的重力。 例如,由于地球如此巨大,它吸引你和你的办公桌的力度比吸引你和办公桌的力度要强。 这就是为什么你和办公桌在地板上保持原位,而不是相互向上移动。
    • Objects that are closer together have a stronger force of gravity between them. For example, the moon is closer to Earth than it is to the more massive sun, so the force of gravity is greater between the moon and Earth than between the moon and the sun. That’s why the moon circles around Earth rather than the sun. You can see this in the Figure .
      ::更为接近的物体在它们之间具有较强的引力。例如,月亮比较大型的太阳更接近地球,因此月球和地球之间的引力大于月球和太阳之间的引力。这就是为什么月球环绕地球而不是太阳。您可以从图中看到这一点。

    The gravitational relationship between the Sun, Earth, and Moon.

     

    Launch PLIX Interactive below to  explore the pull of gravity between two massive objects:
    ::下面发射PLIX互动 探索两个大型物体之间的引力拉动:

     

     

    Summary
    ::摘要

    • Newton’s law of universal gravitation states that the force of gravity affects everything with mass in the universe.
      ::牛顿的宇宙引力法则指出 重力影响着宇宙中 任何质量的物体
    • Newton’s law also states that the strength of gravity between any two objects depends on the masses of the objects and the distance between them.
      ::牛顿的法律还规定,两个物体之间的重力取决于物体的重量和它们之间的距离。

    Review
    ::回顾

    1. What is Newton’s law of universal gravitation?
      ::牛顿的普遍引力法则是什么?
    2. Describe the relationship between the masses of two objects and the force of gravity between them.
      ::描述两个物体质量和它们之间的重力之间的关系。
    3. If two objects each have a mass of 10 kg, then the force of gravity between them
      1. is 100 kg.
        ::100公斤。
      2. is constant.
        ::不变。
      3. depends only on their masses.
        ::只取决于他们的大众。
      4. is greater when they are closer together.
        ::当它们更紧密地在一起的时候,它们就更强大了。

      ::如果两个物体的重量为10公斤,则它们之间的重力为100公斤。是恒定的。只取决于它们的质量。当它们相近时,其重力更大。