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  • General

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  • 时势

    A hesitant boy in a helmet stands with a skateboard, observing skaters at a park.

    Cody seems a little reluctant to launch himself down this ramp at Newton’s Skate Park. It will be his first time down the ramp, and he knows from watching his older brother Jerod that he’ll be moving fast by the time he gets to the bottom. The faster he goes, the harder it will be to stop. That’s because of momentum.  
    ::科迪似乎不太愿意从牛顿滑板公园的斜坡上跳下。 这将是他第一次下坡,他从看他的哥哥杰罗德(Jerod)的眼神中知道,他到底部就会快速前进。 他越快走,就越难停止。 这是因为势头。

    What Is Momentum?
    ::什么是动力?

    Momentum is a property of a moving object that makes it hard to stop. The more mass it has or the faster it’s moving, the greater its momentum. Momentum equals mass times and is represented by the equation:
    ::运动动力是一个移动对象的属性,它使得它难以停止。 运动的强度越大,移动越快,动力就越大。 运动动力等于质量时间,以方程式表示:

    Momentum = Mass × Velocity
    ::动力 = 质量 × 速度

    Q : What is Cody’s momentum as he stands at the top of the ramp?
    ::问:科迪站在坡道顶端的动力是什么?

    A : Cody has no momentum as he stands there because he isn’t moving. In other words, his velocity is zero. However, Cody will gain momentum as he starts moving down the ramp and picks up .
    ::答:科迪站在那里没有动静,因为他没有动静。 换句话说,他的速度是零。 然而,科迪在开始从坡道上爬起时会获得动力。

    Q : Cody’s older brother Jerod is pictured in the Figure , he is larger than Cody and has more mass. If Jerod were to travel down the ramp at the same velocity as Cody, who would have greater momentum? Who would be harder to stop?
    ::问题:科迪的哥哥杰罗德在图中被描绘,他比科迪大,质量也更大。 如果耶罗德以与科迪相同的速度沿着坡道行走,谁会有更大的动力呢?谁会更难阻止呢?

    A : Jerod has more mass than Cody, so he would have greater momentum. He would also be harder to stop.
    ::答:耶鲁德的重量比科迪的要大,所以他的势头会更大。他也会更难阻止。

    A boy performing a skateboard trick in mid-air against a blue sky.

    Calculating Momentum
    ::计算动量

    To calculate momentum with the equation above, mass is measured in (kg), and velocity is measured in meters per second (m/s). For example, Cody and his skateboard have a combined mass of 40 kg. If Cody is traveling at a velocity of 1.1 m/s by the time he reaches the bottom of the ramp, then his momentum is:
    ::以以上方程计算速度,质量以(公斤)计,速度以每秒(米/秒)计。例如,科迪及其滑板的总质量为40公斤。如果科迪在到达坡道底部时以1.1米/秒的速度行驶,那么他的动力是:

    Momentum = 40 kg × 1.1 m/s = 44 kg • m/s
    ::动力=40公斤x1.1米/秒=44公斤/米/秒

    Note that the SI unit for momentum is kg • m/s.
    ::请注意,SI股的动力为公斤/米/秒。

    Q : The combined mass of Jerod and his skateboard is 68 kg. If Jerod goes down the ramp at the same velocity as Cody, what is his momentum at the bottom of the ramp?
    ::问题:杰罗德和他的滑板的总质量是68公斤。如果杰罗德以与科迪相同的速度下坡,那么他在坡道底部的动力是什么?

    A : His momentum is:
    ::A:他的势头是:

    Momentum = 68 kg × 1.1 m/s = 75 kg • m/s
    ::动力=68公斤x1.1米/秒=75公斤/米/秒

    Watch the video below to learn more about calculating the momentum of a moving object:
    ::观看下面的视频, 以了解更多关于计算移动对象的动向 :

     

     

    Summary
    ::摘要

    • Momentum is a property of a moving object that makes it hard to stop. It equals the object’s mass times its velocity.
      ::运动动力是移动对象的属性,使得它难以停止。它等于物体的质量乘以其速度。
    • To calculate the momentum of a moving object, multiply its mass in kilograms (kg) by its velocity in meters per second (m/s). The SI unit of momentum is kg • m/s.
      ::为计算移动物体的动量,以公斤(公斤)乘以每秒(米/秒)米的速度乘以其质量,SI动力单位为公斤/秒。

    Review
    ::回顾

    1. Define momentum.
      ::确定势头。
    2. Write the equation for calculating momentum from mass and velocity.
      ::从质量和速度计算动量的方程写成 。
    3. What is the SI unit for momentum?
      ::SI股的动力是什么?
    4. Which skateboarder has greater momentum?
      1. Skateboarder A: mass = 60 kg; velocity = 1.5 m/s
        ::滑板机A:质量=60公斤;速度=1.5米/秒
      2. Skateboarder B: mass = 50 kg; velocity = 2.0 m/s 
        ::滑板机B:质量=50公斤;速度=2.0米/秒

      ::滑板板板A:质量=60公斤;速度=1.5 m/s 滑板机B:质量=50公斤;速度=2.0 m/s