11.3 牛顿第二法

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  牛顿第二法

  

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  These boys are racing around the track at Newton’s Skate Park. The boy who can increase his the most will win the race. Tony, who is closest to the camera in this picture, is bigger and stronger than the other two boys, so he can apply greater force to his skates.
  ::这些男孩在牛顿滑板公园的赛马场周围奔跑。 能够增加最多男孩的赛马胜出。 托尼最接近这张照片的镜头,比其他两个男孩大,更强大,因此他可以将更大的力量运用在滑冰上。

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  Q : Does this mean that Tony will win the race?
  ::问:这是否意味着托尼将赢得比赛?

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  A : Not necessarily, because force isn’t the only factor that affects .
  ::A:不一定,因为武力并不是影响它的唯一因素。

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  Force, Mass, and Acceleration
  ::力、质量和加速

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  Whenever an object speeds up, slows down, or changes direction, it accelerates. Acceleration occurs whenever an unbalanced force acts on an object. Two factors affect the acceleration of an object: the net force acting on the object and the object’s mass. Newton’s second law of motion describes how force and mass affect acceleration. The law states that the acceleration of an object equals the net force acting on the object divided by the object’s mass. This can be represented by the equation:
  ::当一个物体加速、减慢或改变方向时,它就会加速。当一个物体发生不平衡的动作时,加速就会发生。有两个因素影响物体加速:在物体和物体质量上活动的净力。牛顿的第二项运动法说明了力和质量如何影响加速。法律规定,一个物体加速速度等于物体除以物体质量的物体上行动的净力。这可以用方程式表示:

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  $\begin{array}{r}\mathrm{A}\mathrm{c}\mathrm{c}\mathrm{e}\mathrm{l}\mathrm{e}\mathrm{r}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}=\frac{\mathrm{N}\mathrm{e}\mathrm{t}\mathrm{f}\mathrm{o}\mathrm{r}\mathrm{c}\mathrm{e}}{\mathrm{M}\mathrm{a}\mathrm{s}\mathrm{s}}\end{array}$
  ::加速=NetforceMass

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  or $\begin{array}{r}\mathrm{a}=\frac{\mathrm{F}}{\mathrm{m}}\end{array}$
  ::或 a= Fm

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  Q : While Tony races along on his rollerblades, what net force is acting on the skates?
  ::问:当Tony骑着滚轮滑刀赛跑时,

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  A : Tony exerts a backward force against the ground, as you can see in the Figure , first with one skate and then with the other. This force pushes him forward. Although partly counters the forward motion of the skates, it is weaker than the force Tony exerts. Therefore, there is a net forward force on the skates.
  ::A:托尼对地面施加了后向力量,正如你从图中看到的那样,先是滑冰,然后是滑冰。这股力量将他推向前进。虽然部分地反击了滑冰的前向运动,但它比托尼的实力弱。因此,滑冰上有一支前向力量。

  

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  Watch the video below to learn more about Newton's second law and the relationship between force, mass, and acceleration:
  ::更多了解牛顿的第二定律以及力量、质量和加速度之间的关系:

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  Direct and Inverse Relationships
  ::直接关系和反关系

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  Newton’s second law shows that there is a direct relationship between force and acceleration. The greater the force that is applied to an object of a given mass, the more the object will accelerate. For example, doubling the force on the object doubles its acceleration.
  ::牛顿的第二项法律显示,力与加速之间存在直接关系。 力越强,对特定质量对象的力就越强,物体的加速度就越高。 比如,将物体上的力增加一倍,加速度就会加倍。

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  The relationship between mass and acceleration is different. It is an inverse relationship. In an inverse relationship, when one variable increases, the other variable decreases. The greater the mass of an object, the less it will accelerate when a given force is applied. For example, doubling the mass of an object results in only half as much acceleration for the same amount of force.
  ::质量和加速度之间的关系是不同的。 它是一种反向关系。 在反向关系中, 当一个变量增加时, 另一个变量减少。 一个对象的质量越大, 当应用给定的力时,它的速度就越快。 例如, 将一个对象的质量增加一倍, 使相同强度的加速率只有一半。

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  Q : Tony has greater mass than the other two boys he is racing (pictured in the opening image). How will this affect his acceleration around the track?
  ::问:Tony比其他两个赛马男孩的重量要大(在开场图中描绘)。这将如何影响赛马场周围的加速度?

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  A : Tony’s greater mass will result in less acceleration for the same amount of force.
  ::答:托尼的重量越大, 同样的力量的加速度就越低。

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  Summary
  ::摘要

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  • Newton’s second law of motion states that the acceleration of an object equals the net force acting on the object divided by the object’s mass.
    ::牛顿的第二项运动法规定,物体加速速度等于物体按物体质量分开的物体上的净功率。
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  • According to the second law, there is a direct relationship between force and acceleration and an inverse relationship between mass and acceleration.
    ::根据第二项法律,武力与加速有直接关系,质量与加速有反向关系。

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  Review
  ::回顾

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  1. State Newton’s second law of motion.
     ::州牛顿的第二项诉讼法。
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  2. How can Newton’s second law of motion be represented with an equation?
     ::如何用等式来代表牛顿的第二项运动法?
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  3. If the net force acting on an object doubles, how will the object’s acceleration be affected?
     ::如果物体的净功率加倍,该物体的加速度将受到何种影响?
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  4. Tony has a mass of 50 kg, and his friend Sam has a mass of 45 kg. Assume that both friends push off on their rollerblades with the same force. Explain which boy will have greater acceleration.
     ::托尼的重量为50公斤,他的朋友Sam的重量为45公斤。假设两个朋友都用同样的力力推开他们的滚轮刀。请解释哪个男孩的加速度更高。

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  Explore More
  ::探索更多

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  Use this resource to answer the questions that follow: 
  ::使用此资源回答下列问题:

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  1. How is force proportional to acceleration?
     ::武力如何与加速成比例?
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  2. How is force proportional to mass?  
     ::武力如何与质量成比例?