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  • 武力力力力力力

    A boy performing a trick on a scooter at a skate park under blue skies.

    Jean  has been riding a scooter for almost as long as he can remember. As you can see, he’s really good at it. He can even do tricks in the air. It takes a lot of practice to be able to control a scooter like this. Jean automatically applies just the right forces to control his scooter.  
    ::Jean骑摩托车的时间几乎已经够长了。 正如你所看到的,他非常擅长驾驶。他甚至可以在空中耍花招。 要控制这样的摩托车需要大量实践才能。 Jean自动运用正确的力量来控制他的摩托车。

    Defining Force
    ::定义力力

    Force is defined as a push or pull acting on an object. There are several fundamental forces in the universe, including the force of gravity, electromagnetic force, and weak and strong nuclear forces. When it comes to the motion of everyday objects, however, the forces of interest include mainly gravity, , and applied force. Applied force is force that a person or thing applies to an object.
    ::强制是指对物体的推力或拉力。宇宙中存在几种基本力量,包括重力、电磁力、弱力和强力核力量。然而,在日常物体运动方面,有关力量主要包括重力、力力和力。应用武力是指一个人或东西适用于物体的力量。

    Q : What forces act on Jean ’s scooter?
    ::问题:什么力量对Jean的摩托车采取行动?

    A : Gravity, friction, and applied forces all act on Jean ’s scooter. Gravity keeps pulling both  Jean and the scooter toward the ground. Friction between the wheels of the scooter and the ground prevent the scooter from sliding but also slow it down. In addition,  Jean applies forces to his scooter to control its and direction.
    ::甲:重力、摩擦和运用力都对让的摩托车采取行动。 重力将让和摩托车都拉向地面。 摩擦和地面之间的摩擦阻止了摩托车滑动,也放慢了滑动速度。 此外,让将力推到他的摩托车上来控制它和方向。

    Force and Motion
    ::武力和动力

    Forces cause all motions. Every time the motion of an object changes, it’s because a force has been applied to it. Force can cause a stationary object to start moving or a moving object to change its speed or direction or both. A change in the speed or direction of an object is called . Look at Jean ’s brother  Gordon  in the Figure . He’s getting his scooter started by pushing off with his foot. The force he applies to the ground with his foot starts the scooter moving in the opposite direction. The harder he pushes against the ground, the faster the scooter will go.
    ::力量导致所有动作。 每次物体运动改变时,都是因为对物体施压。 武力可以使静止物体开始移动, 或使移动物体改变速度或方向, 或两者兼而有之。 物体的速度或方向的改变被称作 。 看看图中Jean 的哥哥戈登。 他用脚推开滑板车,从脚推开。 他用脚踏地的力使滑板车向相反的方向移动。 他越是往地推,滑板车越是越快。

    A boy wearing a helmet pushes off with his foot on a scooter in a park.

    How much an object accelerates when a force is applied to it depends not only on the strength of the force but also on the object’s mass. For example, a heavier scooter would be harder to accelerate.  Gordon would have to push with more force to start it moving and move it faster. 
    ::当对物体施用武力时,物体会加速多少速度,不仅取决于力量的强度,而且取决于物体的质量。 比如,更重的摩托车将更难加速。 戈登将不得不用更大的力来启动它并加速移动。

    Q : What units do you think are used to measure force?
    ::问:你认为用哪些单位来衡量武力?

    A : The SI unit for force is the Newton (N). A Newton is the force needed to cause a mass of 1 kilogram to accelerate at 1 m/s 2 , so a Newton equals 1 kg • m/s 2 . The Newton was named for the scientist Sir Isaac Newton, who is famous for his laws of motion and gravity.
    ::A:SI力单位是牛顿(N)。牛顿是造成1公斤重量以1米/秒的速度加速所需的力量,因此牛顿等于1公斤/秒。 牛顿是科学家Isaac Newton爵士的名字,他以运动和重力法而出名。

    Force as a Vector
    ::作为矢量强制力

    Force is a vector , or a measure that has both size and direction. For example,  Gordon pushes on the ground in the opposite direction that the scooter moves, so that’s the direction of the force he is applies. He can give the scooter a strong push or a weak push. That’s the size of the force. Like other vectors, a force can be represented with an arrow. You can see some examples in the Figure . The length of each arrow represents the strength of the force, and the way the arrow points represents the direction of the force.
    ::力是一种向量, 或一种具有大小和方向的量度。 例如, Gordon 将脚踏车向相反的方向推倒在地面上, 推向滑行车移动的方向, 这就是他所应用的力的方向。 他可以给滑行车以强大的推力或微弱的推力。 这就是力的大小。 与其他向量一样, 一种力可以用箭头代表。 您可以在图中看到一些例子。 每个箭头的长度代表着力的强度, 以及箭头指针代表力方向的方式 。

    Examples of force vectors illustrating directions and strengths of forces applied.

    Q : How could you use arrows to represent the forces that start Gordon ’s scooter moving?
    ::问:你如何用箭头来代表发动戈登滑板车动动的力量?

    A :  Gordon pushes against the ground behind him (to the right in the Figure ). The ground pushes back with equal force to the left, causing the scooter to move in that direction. Force arrows A and B (in example 2 in the Figure ) could represent these forces.
    ::A:戈登将他身后的地面推向(图中向右 ) 。 地面以等力向左推向后,导致摩托车朝这个方向移动。 部队箭头A和B(图中的例子2)可以代表这些力量。

    Summary
    ::摘要

    • Force is defined as a push or pull acting on an object. Forces include gravity, friction, and applied force.
      ::力是指对物体的推力或拉力作用。力包括重力、摩擦和施加力。
    • Force causes changes in the speed or direction of motion. These changes are called acceleration.
      ::动力导致运动速度或方向的变化。这些变化被称为加速。
    • The SI unit for force is the Newton (N).
      ::SI力力单位是牛顿(N)。
    • Force is a vector because it has both size and direction. Like other vectors, it can be represented by an arrow.
      ::强制是矢量, 因为它既具有大小, 也具有方向。 与其他矢量一样, 它可以用箭头代表 。

    Review
    ::回顾

    1. What is force?
      ::什么是力量?
    2. Relate force and motion.
      ::相对武力和动议。
    3. What forces control the motion of everyday objects?
      ::什么力量控制日常物体的移动?
    4. Identify and define the SI unit for force.
      ::确定和界定SI部队。
    5. Draw a diagram to represent a foot kicking a resting soccer ball. Use arrows to represent the force applied to the ball and to show how the ball moves after it is kicked. 
      ::绘制图表以代表脚踢休养足球球。 使用箭头来表示球所应用的力量, 并显示球被踢后如何移动 。