3.3 连接牛顿第一和第二法律

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  连接牛顿第一和第二法律

  

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  This image is of Buzz Aldrin, one of the first men to walk on the moon. Apollo 11 was the spaceflight that landed the first humans, Neil Armstrong and Buzz Aldrin, on the moon on July 20, 1969. Armstrong became the first to step onto the lunar surface 6 hours later on July 21. As you probably already know, men weigh less on the moon than on Earth; this is because the force of gravity is less on the moon than on Earth.
  ::这是巴斯·阿尔德林(Buzz Aldrin)的图像,他是最早在月球上行走的人之一。阿波罗11号是1969年7月20日登月的航天飞机,搭载第一批人尼尔·阿姆斯特朗和巴斯·阿尔德林(Baz Aldrin)登月。阿姆斯特朗在7月21日6小时后成为第一个登月球表面的人。 正如你可能已经知道的那样,人类在月球上比在地球上的重量要低;这是因为在月球上的引力比在地球的引力要小。

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  What is a force?
  ::什么是力量?

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  Newton’s First and Second Laws of Motion
  ::牛顿第一和第二号运动法

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  A force is a push or a pull on an object. When you place a book on a table, the book pushes downward on the table and the table pushes upward on the book. The two forces are equal and there is no resulting motion of the book. If, on the other hand, you hold the book in the air and let go, the force of gravity will pull the book to the ground.
  ::一种力量就是对一个对象的推力或拉力。当你把一本书放在一张桌子上时, 书会往下推, 桌子会往上推。 两个力量是相等的, 书不会因此产生运动。 另一方面, 如果你把书放在空中放走, 引力会把书拉到地上 。

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  If you slide a book across the floor or a table, the book will experience a frictional force, which acts in the opposite direction of the motion. This force will slow down the motion of the book and eventually bring it to rest. A smoother surface has a smaller force of , which will allow the book to slide further before coming to rest. If a perfectly smooth floor could be created, there would be no friction and the book would slide forever at constant .
  ::如果您将一本书滑过地板或桌子, 这本书将经历摩擦力, 摩擦力与运动相反。 这支力量将减慢这本书的动作, 并最终让它得到休息。 更平滑的表面有小的 . 使书在休息前能进一步滑动。 如果可以建立完全平滑的地板, 就不会有摩擦, 这本书将永远持续地滑动 。

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  Newton’s First Law of Motion states that an object at rest will stay at rest and an object in motion will remain in motion. It describes a phenomenon called . Inertia is the tendency of an object to resist change in its state of motion. In the absence of any force, an object will continue to move at the same constant speed and in the same straight line. If the object is at rest, in the absence of any force, it will remain at rest. Newton’s First Law states that an object with no force acting on it moves with constant . (The constant velocity could, of course, be 0 m/s.)
  ::牛顿的第一个运动法则规定,休息的物体将保持休息,运动的物体将保持活动状态。它描述了一种被称为“不动”的现象。一个物体倾向于抵制运动状态的改变。在没有任何武力的情况下,一个物体将继续以同样的不变速度和在同一直线上移动。如果物体处于休息状态,在没有武力的情况下,它将保持休息状态。牛顿的第一法则规定,一个没有武力的物体以恒定的速度移动。 (当然,恒定速度可以是0米/秒。 )

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  According to Newton’s First Law, is a force needed to keep a sled sliding on ice at a constant velocity? Use the simulation below to discover more:
  ::根据牛顿的第一定律,是否需要一支力量来保持冰雪滑动的恒定速度? 用下面的模拟来发现更多:

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  Newton’s First Law is equivalent to saying that “if there is no net force on an object, there will be no .” In the absence of acceleration, an object will remain at rest or will move with constant velocity in a straight line. The acceleration of an object is the result of an unbalanced force. If an object undergoes two forces, the motion of the object is determined by the net force. The magnitude of the acceleration is directly proportional to the magnitude of the unbalanced force. The direction of the acceleration is the same direction as the direction of the unbalanced force. The magnitude of the acceleration is inversely proportional to the mass of the object; the more massive the object, the smaller the acceleration produced by the same force.
  ::牛顿的第一法则相当于说“如果一个物体上没有净力,就不会有净力 ” 。 如果没有加速,一个物体将保持休息或以恒定速度在直线上移动。一个物体的加速是不平衡力的结果。如果一个物体经历了两股力,物体的动作由净力决定。加速力的大小与不平衡力的大小直接成正比。加速力的方向与不平衡力的方向相同。加速力的大小与物体的质量成反比;物体的加速力越大,同一力量产生的加速力就越小。

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  These relationships are stated in Newton’s Second Law of Motion : "the acceleration of an object is directly proportional to the net force on the object and inversely proportional to the mass of the object."
  ::这些关系在牛顿第二定律运动中写道:“物体的加速率直接与物体的净力成正比,与物体的质量成反比。”

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  Newton’s Second Law can be summarized in an equation:
  ::牛顿的《第二法》可以用一个方程式来概括:

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  $\begin{array}{r}a=\frac{F}{m}\end{array}$ or more commonly, $\begin{array}{r}F=ma\end{array}$
  ::a=Fm或更常见的,F=ma

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  According to Newton’s Second Law, a new force on an object causes it to accelerate. However, the larger the mass, the smaller the acceleration. We say that a more massive object has a greater inertia.
  ::根据牛顿的《第二法》,物体上的新力量导致其加速。 然而,质量越大,加速度越小。 我们说,更大规模物体的惯性越大。

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  The units for force are defined by the equation for Newton’s Second Law. Suppose we wish to express the force that will give a 1.00 kg object an acceleration of 1.00 m/s ² .
  ::力力单位由牛顿第二法则的方程式来定义。 假设我们想表达给一千克物体以1.00 m/s2加速度的力的话。

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  $\begin{array}{r}F=ma=(1.00\text{kg})(1.00{\text{m/s}}^2)=1.00\text{kg}\cdot {\text{m/s}}^2\end{array}$
  ::F=ma=(1.00公斤)(1.00米/秒)=1.00千克/秒)

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  This unit is defined as 1.00 newton or 1.00 N.
  ::该单位的定义为1.00牛顿或1.00牛顿。

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  $\begin{array}{r}\frac{kg\cdot m}{s^2}=\text{newton}\end{array}$
  ::立方公尺@ ms2 = newton

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  What Forces are Acting on You? 
  ::什么力量在对你采取行动?

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  A classic physics example of the applications of Newton’s Second Law is the acceleration we experience while riding in an elevator. How can you accelerate upward if your (or the force due to gravity) always remains the same? At what points are you speeding up in the elevator? Slowing down? Moving at a constant rate? What is the net force required for these accelerations to occur? Use the simulation below to explore these questions and gain a deeper understanding of Newton’s Second Law:
  ::牛顿第二定律应用的经典物理实例是我们在电梯中加速飞行。 如果(或重力)始终不变,你如何能向上加速? 在什么点上加快电梯? 减速? 以恒定速度移动? 这些加速飞行所需要的净力是什么? 利用下面的模拟来探索这些问题,并加深对牛顿第二定律的理解:

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  Examples
  ::实例

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  Example 1  
  ::例1

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  What force is required to accelerate a 2000. kg car at 2.000 m/s ² ?
  ::加速2000公斤2 000米/秒的汽车需要何种武力?

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  $\begin{array}{r}F=ma=(2000.\text{kg})(2.000{\text{m/s}}^2)=4000.\text{N}\end{array}$
  ::F=ma=(2000公斤)(2 000米/秒)=400.00.N

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  Example 2  
  ::例2

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  A net force of 150 N is exerted on a rock. The rock has an acceleration of 20. m/s ² due to this force. What is the mass of the rock?
  ::由于这种力量,岩石的加速度为20米/秒。岩石的质量是多少?

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    $\begin{array}{r}m=\frac{F}{a}=\frac{(150\text{N})}{(20.{\text{m/s}}^2)}=7.5\text{kg}\end{array}$
  ::m=FA=(150 N)(20.m/s2)=7.5公斤

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  Example 3  
  ::例3

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  A net force of 100. N is exerted on a ball. If the ball has a mass of 0.72 kg, what acceleration will it undergo?
  ::球的净功率为100 N,如果球质量为0.72公斤,会加速到什么程度?

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    $\begin{array}{r}a=\frac{F}{m}=\frac{(100.\text{N})}{(0.72\text{kg})}=140{\text{m/s}}^2\end{array}$
  ::a=Fm=(100.N(0.72公斤)=140m/s2)

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  Apply Newton’s Second Law in this simulation to determine the acceleration of an airboat with a given mass and a variety of forces acting on it:
  ::在模拟中应用牛顿的第二定律来确定具有一定质量和各种力量的航空船加速速度:

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  Further Reading
  ::继续阅读

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  • Newton's First Law
    ::牛顿第一法

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  Summary
  ::摘要

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  • A force is a push or pull on an object.
    ::力量是推力或拉动物体。
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  • Newton’s First Law states that an object with no net force acting on it remains at rest or moves with constant velocity in a straight line.
    ::牛顿的第一定律指出,一个没有净力作用的物体仍处于休息状态,或以恒定速度直线移动。
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  • Newton’s Second Law states that the acceleration of an object is directly proportional to the net force on the object and inversely proportional to the mass of the object.
    ::牛顿的《第二项法律》规定,物体加速率与物体的净力成正比,与物体的质量成反比。
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  • Newton’s Second Law is expressed as an equation, $\begin{array}{r}F=ma\end{array}$ .
    ::牛顿的第二法则以方程式F=ma表示。

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  Review
  ::回顾

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  1. A car of mass 1200 kg traveling westward at 30. m/s is slowed to a stop in a distance of 50. m by the car’s brakes. What was the braking force?
     ::一辆1200公斤重的汽车在30米/秒向西行驶,在车刹车50米的距离内被减速到停车。 制动部队是什么?
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  2. Calculate the average force that must be exerted on a 0.145 kg baseball in order to give it an acceleration of 130 m/s ² .
     ::计算在0.145公斤棒球上必须施加的平均力,使其加速度达到130 m/s2。
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  3. After a rocket ship going from the Earth to the moon leaves the gravitational pull of the Earth, it can shut off its engine and the ship will continue on to the moon due to the gravitational pull of the moon.
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     1. True
        ::真实
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     2. False
        ::假假
     
     ::从地球到月球的火箭飞船离开地球引力拉动后,它可以关闭引擎,由于月球引力拉动,船将继续飞向月球。
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  4. If a space ship traveling at 1000 miles per hour enters an area free of gravitational forces, its engine must run at some minimum level in order to maintain the ships velocity.
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     1. True
        ::真实
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     2. False
        ::假假
     
     ::如果以每小时1 000英里的速度航行的航天船进入无引力区域,其发动机必须至少运行一定水平,以保持船只的速度。
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  5. Suppose a space ship traveling at 1000 miles per hour enters an area free of gravitational forces and free of air resistance. If the pilot wishes to slow the ship down, he can accomplish that by shutting off the engine for a while.
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     1. True
        ::真实
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     2. False
        ::假假
     
     ::假设一艘时速1000英里的太空船进入一个无引力和无空气阻力的区域。 如果飞行员希望放慢飞船的速度,他可以通过关闭引擎一段时间来达到这个目的。真假。

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  Explore More
  ::探索更多

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

   

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  1. What is a Hero’s Engine?
     ::英雄的引擎是什么?
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  2. How does Newton’s First Law of Motion have to do with the Hero’s Engine?
     ::牛顿的第一定律与英雄的引擎有什么关系?
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  3. Why does the yellow ball go further?
     ::为什么黄球会更进一步?