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【英语时差8,16】步枪及相关法律

时间：2015-12-02 05:24:01

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（单词翻译）

There's a law that says that when you fire a rifle, you'll get smacked2. And it won't be by a policeman: the rifle itself will smack1 you right on the shoulder. This is due to the rifle's "recoil3." Today, A Moment of Science looks at the law behind recoil.  A rifle recoils4 because of the law of momentum5. This law says that momentum is always conserved6, or to put it another way, every action has an equal and opposite reaction. So, the forward momentum of the bullet equals the backward momentum of the recoil. How can the momentum of the bullet and the recoil be equal? Bullets are fast as---a speeding bullet.
It's not speed that must balance: it's momentum. Momentum depends on speed and mass. While bullets have a very small mass and a very fast speed, rifles have a relatively7 large mass compared to a bullet, so the recoil has a relatively slow speed. The small and fast bullet balances the larger and slower rifle.
If recoil is a law of physics, it must happen every time a rifle is fired, but we know that hunters aren't beaten black and blue by their own rifles. Holding the rifle tightly to the shoulder makes the law of momentum work for you instead of against you. When you hold a rifle this way, you make your body and the rifle act as one unit. Now, the forward momentum of the bullet must equal the backward momentum of the new rifle-person unit. The mass of the rifle and person together is so huge that the speed of the recoil becomes very small.  
 

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点击收听单词发音收听单词发音  

1 smack XEqzV     
vt.拍，打，掴；咂嘴；vi.含有…意味；n.拍
参考例句：
  • She gave him a smack on the face.她打了他一个嘴巴。
  • I gave the fly a smack with the magazine.我用杂志拍了一下苍蝇。
2 smacked bb7869468e11f63a1506d730c1d2219e     
拍，打，掴( smack的过去式和过去分词 )
参考例句：
  • He smacked his lips but did not utter a word. 他吧嗒两下嘴，一声也不言语。
  • She smacked a child's bottom. 她打孩子的屁股。
3 recoil GA4zL     
vi.退却，退缩，畏缩
参考例句：
  • Most people would recoil at the sight of the snake.许多人看见蛇都会向后退缩。
  • Revenge may recoil upon the person who takes it.报复者常会受到报应。
4 recoils e70b34ddcfc6870bc5350c1614b48cfc     
n.（尤指枪炮的）反冲，后坐力( recoil的名词复数 )v.畏缩( recoil的第三人称单数 )；退缩；报应；返回
参考例句：
  • A gun recoils after being fired. 枪在射击后向后坐。 来自《现代英汉综合大词典》
  • A molecule striking an advancing piston recoils with increased speed. 撞在前进中的活塞上的分子，会加速反跳。 来自辞典例句
5 momentum DjZy8     
n.动力，冲力，势头；动量
参考例句：
  • We exploit the energy and momentum conservation laws in this way.我们就是这样利用能量和动量守恒定律的。
  • The law of momentum conservation could supplant Newton's third law.动量守恒定律可以取代牛顿第三定律。
6 conserved d1dc02a3bfada72e10ece79fe3aa19af     
v.保护，保藏，保存( conserve的过去式和过去分词 )
参考例句：
  • He conserved his energy for the game. 他为比赛而养精蓄锐。 来自《简明英汉词典》
  • Under these conditions, the total mechanical energy remains constant, or is conserved. 在这种条件下，总机械能保持不变或机械能保存。 来自辞典例句
7 relatively bkqzS3     
adv.比较...地，相对地
参考例句：
  • The rabbit is a relatively recent introduction in Australia.兔子是相对较新引入澳大利亚的物种。
  • The operation was relatively painless.手术相对来说不痛。

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