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  • 牛顿第三法

    A Space Elevator As A Transportation Link Between Earth And Space.

    The image above is a NASA artist’s conceptual illustration of a space elevator. It was imagined as a geo-stationary transfer station for passengers and cargo between Earth and space. This idea was not pursued beyond the initial discussion and evaluation stage, but the scientists involved believe the concept will become truly possible with the expected technological advances of the late 21 st century.
    ::以上图像是美国航天局艺术家对空间电梯的概念性说明。 它被想象成地球与空间之间客运和货运的地球静止转移站。 这一想法在初步讨论和评估阶段之后并没有被采纳,但参与的科学家认为,随着21世纪末期的预期技术进步,这一概念将真正成为可能。

    Newton’s Third Law of Motion
    ::牛顿的第三项运动法

    Where do forces come from? Observations suggest that a force applied to an object is always applied by another object. A hammer strikes a nail, a car pulls a trailer, and a person pushes a grocery cart. Newton realized that forces are not so one-sided. When the hammer exerts a force on the nail, the nail also exerts a force on the hammer—after all, the hammer comes to rest after the interaction. This led to Newton’s Third Law of Motion , which states that whenever one object exerts a force on a second object, the second object also exerts a force on the first object, equal in magnitude and opposite in direction.
    ::观察显示,一个物体所应用的武力总是被另一个物体所应用。 锤子敲钉,汽车拉拖车,一个人推杂货车。 牛顿意识到,武力不是那么单方面的。 当锤子对钉子施加武力时,钉子也对锤子施加了力量 — — 毕竟,锤子在互动之后就停了下来。 这导致了牛顿的《第三项运动法》,其中指出,每当一个物体对第二个物体施加武力时,第二个物体也对第一个物体施加力量,其规模和方向都相等。

     

     

    This law is sometimes paraphrased as: “For every action, there is an equal and opposite reaction.” A very important point to remember is that the two forces are on different objects—never on the same object. It is frequently the case that one of the objects moves as a result of the force applied but the motion of the other object in the opposite direction is not apparent.
    ::这项法律有时被解释为: " 对于每一项行动,都有平等和相反的反应 " 。 需要记住的一个非常重要的一点是,这两股力量在不同的物体上,而不是在同一物体上。 经常的情况是,其中一个物体因所施的武力而移动,而另一个物体朝着相反的方向移动并不明显。

    Consider the situation where an ice skater is standing at the edge of the skating rink holding on to the side rail. If the skater exerts a force on the rail, the rail is held in place with tremendous and therefore, will not move in any noticeable way. The skater, on the other hand, had little friction with the ice, and therefore will be accelerated in the direction opposite of her original push. This is the process people use to jump up into the air. The person's feet exert force on the ground and the ground exerts an equal and opposite force on the person's feet. The force on the feet is sufficient to raise the person off the ground. The force on the ground has little effect because the Earth is so large. One of the accelerations is visible but the other is not visible.
    ::考虑一下滑冰者站在滑冰场边缘的侧铁轨上的情况。 如果滑冰者在铁路上施压, 铁路会以巨大的速度保持, 因此不会以任何明显的方式移动。 另一方面,滑冰者与冰的摩擦很小, 因此会加速到与她最初的推力相反的方向。 这就是人们跳入空中的过程。 一个人的脚在地面上施压, 地面对人的脚施加同等和相反的力量。 脚上的力量足以将人抬离地面。 地面上的力量由于地球如此之大而没有什么作用。 一种加速是可见的, 而另一种是看不见的。

    A case where the reaction motion due to the reaction force is visible is the case of a person throwing a heavy object out of a small boat, such as a kayak. The object is accelerated in one direction and the boat is accelerated in the opposite direction. In this case, both the motion of the object is visible and the motion of the boat in the opposite direction is also visible.  Explore the resulting motion of two interacting objects as a result of Newton’s Third Law in this Pirate Ship simulation below:
    ::由反应力引起的反应动议显而易见的情况是,有人从一艘小型船只上扔出重物,如皮艇。物体在一个方向加速,而船只在相反方向加速。在这种情况下,物体的移动是可见的,船只的移动是可见的。

    Rockets also work in this manner. It is a misconception that the rocket moves forward because the escaping gas pushes on the ground or the surrounding air to make the rocket go forward. Rockets work in outer space where there is no ground or surrounding air. The rocket exerts a force on the gases causing them to be expelled and the gases exert a force on the rocket causing it to be accelerated forward.
    ::火箭也是以这种方式运作的,这是一种误解,即火箭前进是因为逃避的气体在地面或周围空气中推推,使火箭向前推进,火箭在没有地面或周围空气的外层空间工作,火箭对气体施加武力,导致气体被驱逐,而气体对火箭施加武力,使火箭加速前进。

    The applications of Newton’s Third Law can also be explored in the classic example if a horse pulling a cart. How does the horse-cart system move if the cart pulls on the horse with the same exact force and in the opposite direction as the horse pulls on the cart? (Beware, there are many misconceptions related to this example! Always remember that Newton’s Third Law applies to the same type of force acting on different objects).
    ::牛顿第三法则的应用也可以在经典例子中探讨,如果马拉着一辆马车的话。 如果马车用与马拉着相同的力力和相反的方向拉着马,马车系统如何移动? (请注意,与这个例子相关的误解很多!请记住牛顿第三法则适用于对不同物体的同样类型的力。 )

    Summary
    ::摘要

    • A force applied to an object is always applied by another object.
      ::对象所应用的强制力总是被另一个对象所应用。
    • Newton’s Third Law of Motion states, “Whenever one object exerts a force on a second object, the second object also exerts a force on the first object, equal in magnitude and opposite in direction.”
      ::牛顿的《第三项运动法》指出,“当一个物体对第二个物体施压时,第二个物体也对第一个物体施压,其强度相等,方向相反。”

    Review
    ::回顾

    1. What is wrong with the following statement: When you exert a force on a baseball, the equal and opposite force on the ball balances the original force and therefore, the ball will not accelerate in any direction.
      ::下述说法有什么错:在对棒球施压时,球上的平等和相反的力量平衡了最初的力量,因此,球不会向任何方向加速。
    2. When a bat strikes a ball, the force exerted can send the ball deep into the outfield. Where is the equal and opposite force in this case?
      ::当蝙蝠打球时,所施加的力量可以把球送到外野深处。 在这种情况下,平等和相反的力量在哪里?
    3. Suppose you wish to jump horizontally and in order for you to jump a distance of 4 feet horizontally, you must exert a force of 200 N. When you are standing on the ground, you have no trouble jumping 4 feet horizontally. If you are standing in a canoe, however, and you need to jump 4 feet to reach the pier, you will surely fall into the lake. Why is it that you cannot jump 4 feet out of a canoe when you can easily do this when on land?
      ::假设你想水平跳跃,为了让您水平跳跃四英尺的距离,你必须施加200N的力量。当你站在地上时,你没有困难地水平跳四英尺。但是,如果你站在独木舟中,需要跳四英尺才能到达码头,你肯定会掉进湖里。为什么你可以在陆地上轻而易举地跳出四英尺独木舟呢?

    Explore More
    ::探索更多

    Use the resource below to answer the questions that follow.
    ::利用以下资源回答以下问题。

    1. What does the bottle rocket have to do with Newton’s Third Law of Motion?
      ::瓶装火箭与牛顿的《第三定律》有什么关系?