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  • 牛顿第三法

    Sketch of a person on a skateboard, illustrating movement and Newton's Third Law.

    This is a sketch of Jerod on his skateboard. He’s on his way to Newton’s Skate Park. When he pushes his foot against the ground, what happens next? He moves on his skateboard in the opposite direction. How does this happen?
    ::这是Jerod在滑板上的草图。 他正在前往牛顿滑板公园的路上。 当他脚踩地时,接下来会怎样? 他从滑板上向相反的方向移动。 怎么会这样呢?

    Action and Reaction
    ::行动和反应

    Newton’s third law of motion explains how Jerod starts his skateboard moving. This law states that every action has an equal and opposite reaction. This means that forces always act in pairs. First, an object applies a force on a second object—Jerod pushes against the ground with his foot. Then, the second object applies an equal and opposite reaction force on the first object—the ground pushes back on Jerod! This force from the ground causes Jerod to move forward. The reaction force is always equal in strength to the action force but in the opposite direction.
    ::牛顿的第三个运动法解释Jerod是如何开始滑板运动的。 该法规定,每个动作都有相同和相反的反应。 这意味着武力总是一对一对。 首先,一个物体在第二个物体上施用武力,Jerod用脚对着地面。 然后,第二个物体在第一个物体上施用相同和相反的反应力 — — 地面向Jerod推倒!这股力量从地面使Jerod向前移动。反应力总是与战斗力一样,但方向相反。

    Q : If Jerod pushes against the ground with greater force, how will this affect his forward motion?
    ::问:如果耶鲁德用更大的武力推倒地面,这将如何影响他的前进运动?

    A : The action force applied to the ground will be greater, so the reaction force applied to Jerod on his skateboard will also be greater. The ground will push Jerod forward with more force, making him go faster and farther.
    ::A:地面上的行动力将更大,因此滑板上对Jerod的反应力也将更大。 地面将用更大的力量推动Jerod前进,使他走得更快、更远。

    Equal and Opposite Forces
    ::平等和对面部队

    The forces involved in actions and reactions can be represented with arrows. The direction of the arrow shows the direction of the force, and the length of the arrow shows how strong the force is. Look at the skateboarders in the Figure . In the top row, the arrows represent the action forces with which the skateboarders push against each other. In the middle row, the arrows represent the reaction forces on the skateboarders. This is the reaction. Compare the arrows for the action and reaction forces. They point in different directions, but they are the same length. This shows that the reaction forces are equal in strength and opposite in direction to the action forces.
    ::参与行动和反应的力量可以用箭头表示。 箭头的方向显示力量的方向, 箭头的长度显示力量的强度。 看看图中的滑板运动员。 在顶行, 箭头代表滑板运动员相互推动的动作力量。 在中行, 箭头代表滑板运动员的反应力量。 这是反应。 将箭头比对动作和反应力量。 它们指向不同的方向, 但长度相同。 这显示反应力量在力量上与动作力量相反。

    Action and reaction forces between skateboarders with arrows indicating force directions.

    Equal and Opposite but Not Balanced
    ::平等、对面但非平衡

    Action and reaction forces are always equal and opposite, but they do not cancel out like balanced forces. Balanced forces are equal and opposite forces that act on the same object, so they cancel out and do not result in motion. Action-reaction forces are equal and opposite forces that act on different objects, so they can result in motion. For example, when Jerod pushes his skateboard against the ground, the ground pushes back on Jerod and the skateboard with an equal and opposite force. This causes the skateboard to move forward.
    ::行动与反应力量总是平等和对立的,但是它们并没有像平衡力量那样取消。平衡力量是平等和对立的力量,在同一物体上采取行动,因此它们取消并且不导致运动。行动-反应力量是平等和对立的力量,在不同物体上采取行动,因此它们可以导致运动。例如,当Jerod将滑板推向地面时,地面以平等和对立的力量推向Jerod和滑板。这导致滑板向前移动。

    Q : Action and reaction forces occur all the time. Can you think of an example in your daily life?
    ::问题:行动和反应力量总是发生。你能想到日常生活中的一个例子吗?

    A : Here’s one example. If you lean on something like a wall or your locker, you are applying force to it. The wall or locker applies an equal and opposite force to you. If it didn’t, you would go right through it or else it would tip over.
    ::A:这里举一个例子。如果你靠墙壁或储物柜这样的东西,你就会对它施压。 墙壁或储物柜对你施压是相同的。 如果不是,你就会直接穿过它,否则它就会翻过来。

    Watch the video below to learn more about Newton's third law of motion:
    ::更多了解牛顿第三种运动法则:

     

     

    Summary
    ::摘要

    • Newton’s third law of motion states that every action has an equal and opposite reaction. This means that forces always act in pairs.
      ::牛顿的第三个运动法则指出,每个行动都有相同和相反的反应。 这意味着力量总是一对一地行动。
    • Action and reaction forces are equal and opposite, but they are not balanced forces because they act on different objects so they don’t cancel out.
      ::行动与反应力量是平等和对立的, 但他们不是平衡的力量, 因为他们对不同的物体采取行动,

    Review
    ::回顾

    1. State Newton’s third law of motion.
      ::牛顿州第三种诉讼法
    2. Describe an example of an action and reaction. Identify the forces and their directions.
      ::描述一个动作和反应的例子。 确定部队及其方向 。
    3. Explain why action and reaction forces are not balanced forces.
      ::解释为什么行动和反应力量不是平衡力量。

    Explore More
    ::探索更多

    Watch this video about Newton’s third law of motion and then answer the questions that follow:
    ::观看这段关于牛顿第三位运动法则的影片,

     

     

    1. Describe all the forces acting on the  coffee mug as it is resting on the coffee table . 
      ::描述所有在咖啡杯上行动的力量 当它躺在咖啡桌上的时候
    2. Identify one action and reaction force pair involving the coffee mug resting on the coffee table.
      ::确定一对行动和反应力量配对 涉及咖啡杯 放在咖啡桌上的咖啡杯