章节大纲

  • A young skateboarder performs a trick with a skateboard, showcasing enthusiasm and skill.

    There’s no doubt from Corey’s face that he loves skateboarding! Corey and his friends visit Newton’s Skate Park every chance they get. They may not know it, but while they’re having fun on their skateboards, they’re actually applying science concepts such as forces and motion.
    ::科里无疑喜欢滑板。 科里和他的朋友们每有机会都去牛顿滑板公园探险。 他们可能不知道这一点,但是虽然他们在滑板上玩得很开心,但他们实际上在应用力量和运动等科学概念。

    Keep on Rolling
    ::继续滚

    Have you ever ridden a skateboard? If so, then you already know something about Newton’s first law of motion . This law was developed by English scientist Isaac Newton around 1700. Newton was one of the greatest scientists of all time. He developed three laws of motion and the law of gravity, among many other contributions.
    ::你曾经骑过滑板吗? 如果有的话,那么你已经知道牛顿的第一个运动法。 这项法律是英国科学家艾萨克·牛顿在1700年左右制定的。 牛顿是有史以来最伟大的科学家之一。 他制定了三项运动法和重力法,以及其他许多贡献。

    Newton’s first law of motion states that an object at rest will remain at rest and an object in motion will stay in motion unless it is acted on by an unbalanced force. Without an unbalanced force, a moving object will not only keep moving, but its and direction will also remain the same. Newton’s first law of motion is often called the law of because inertia is the tendency of an object to resist a change in its motion. If an object is already at rest, inertia will keep it at rest. If an object is already in motion, inertia will keep it moving.
    ::牛顿的第一部运动法则规定,休息的物体将保持休息,运动的物体将保持活动状态,除非以不平衡的力量采取行动。 没有不平衡的力量,移动的物体将不仅继续前进,而且其方向也将保持不变。 牛顿的第一部运动法则常常被称为“法律 ” , 因为惰性是物体抵制其运动变化的倾向。 如果物体已经处于休息状态,惰性将保持其休息状态。 如果物体已经处于运动状态,惰性将保持其运动状态。 如果物体已经处于运动状态,惰性将保持其运动状态。

    Therefore, a skateboard at rest will remain at rest unless acted upon by an unbalanced force. In the absence of or any other unbalanced force,  a skateboard in motion will just keep on rolling!
    ::因此,除非有一支不平衡的力量采取行动,否则休息的滑板将保持休息。 如果没有一支不平衡的力量或其他任何不平衡的力量,运动中的滑板就会继续滚动!

    Starting and Stopping
    ::开始和停止

    So how do we change motion? You probably know that to start a skateboard rolling over a level surface, you need to push off with one foot against the ground. That’s what Corey’s friend Nina is doing in this picture .
    ::所以,我们如何改变运动?你可能知道,要开始滑板在平面上滚动,你就必须用一只脚踩地面。 科里的朋友尼娜正在这幅画中这样做。

    A person pushing off a skateboard at sunset, demonstrating motion initiation.

    A person stepping on the back of a skateboard to create friction and stop it.

    Do you know how to stop a skateboard once it starts rolling? Look how Nina's friend Laura does it in the Figure . She steps down on the back of the skateboard so it scrapes on the pavement. This creates friction, which stops the skateboard.
    ::你知道如何在滑板开始滚动后停止滑板吗?

    Even if Laura didn’t try to stop the skateboard, it would stop sooner or later. That’s because there’s also friction between the wheels and the pavement. Friction is a force that counters all kinds of motion. It occurs whenever two surfaces come into contact.
    ::即使劳拉没有试图阻止滑板,它也迟早会停止。 这是因为轮子和人行道之间也存在摩擦。 摩擦是一股对抗各种运动的力量。 当两个表面发生接触时,它就会发生。

    Do You Get It?
    ::你明白吗?

    Q : How does Nina use Newton’s first law to start her skateboard rolling?
    ::尼娜如何使用牛顿的第一个法律开始滑板滚动?

    A : The skateboard won’t move unless Nina pushes off from the pavement with one foot. The force she applies when she pushes off is stronger than the force of friction that opposes the skateboard’s motion. As a result, the force on the skateboard is unbalanced, and the skateboard moves forward.
    ::简言之:除非尼娜一脚从人行道上推下来,否则滑板不会移动。 她推出去时所应用的力量比反对滑板运动的摩擦力更强大。 结果,滑板上的力量不平衡,滑板向前移动。

    Q : How does Nina use Newton’s first law to stop her skateboard?
    ::问:尼娜如何使用牛顿第一部法律阻止滑板?

    A : Once the skateboard starts moving, it would keep moving at the same speed and in the same direction if not for another unbalanced force. That force is friction between the skateboard and the pavement. The force of friction is unbalanced because Nina is no longer pushing with her foot to keep the skateboard moving. That’s why the skateboard stops.
    ::甲:当滑板开始移动时,如果不是另一支不平衡的力量,它也会以同样的速度和方向继续移动。 这一力量是滑板和人行道之间的摩擦。 摩擦的力量是不平衡的,因为尼娜不再用脚推着滑板继续移动。 这就是为什么滑板停止了。

    Changing Speed
    ::变化速度

    A person skating on a bank at a skate park, demonstrating motion and friction.

    Corey’s friend Jerod likes to skate on the flat banks at Newton’s Skate Park. That’s Jerod in the Figure . As he rolls down a bank, he sees Corey is about to run into him! To change his speed, he quickly presses his foot against the ground and drags it. This creates a strong friction force that slows him down.
    ::科里的朋友杰罗德喜欢在牛顿滑板公园的平面银行滑冰。 这是《图》中的杰罗德。 当他滑下银行时,他看到科里正要撞到他!为了改变他的速度,他很快将脚踩在地上拖着它。 这造成了强大的摩擦力量,拖慢了他。

    Do You Get It?
    ::你明白吗?

    Q : How does Jerod use Newton’s first law of motion to change the speed of his skateboard?
    ::问:耶洛德如何使用牛顿的第一个运动法则来改变滑板的速度?

    A : Dragging his foot on the ground creates an unbalanced force. The increased force of friction causes his body to slow down and slows the skateboard as well. Jerod knows that his shoes and the top of his board will create lots of friction, allowing him to keep the board from slipping out from under his foot.
    ::甲:将脚拖到地上形成一种不平衡的力量。摩擦力量的增加导致他的身体减慢,滑板也减慢了速度。 耶洛德知道他的鞋和板顶将制造许多摩擦,使他能够防止板子从脚下滑出。

    Summary
    ::摘要

    • Newton’s first law of motion states that an object at rest will remain at rest and an object in motion will remain in motion unless it is acted on by an unbalanced force.
      ::牛顿的第一部运动法规定,休息的物体将保持休息,运动的物体将保持运动,除非以不平衡的力量采取行动。

    Review
    ::回顾

    1. State Newton’s first law of motion.
      ::牛顿州第一部运动法
    2. You don’t need to push off with a foot against the ground to start a skateboard rolling down a bank. Does this violate Newton’s first law of motion? Why or why not?
      ::这是否违反了牛顿的第一部运动法则? 为什么或为什么不呢? 这是否违反了牛顿的首部运动法则?

    A person sits on the ground after falling from a skateboard on pavement.

    1. Jerod ran into a rough patch of pavement, but he thought he could ride right over it. Instead, the skateboard stopped suddenly and Jerod ended up on the ground (see Figure ). Explain what happened.
      ::Jerod跑到路面上,但他认为他可以骑车过路面。 相反,滑板突然停了下来,Jerod最后倒在地上(见图 ) 。 解释发生了什么。
    2. Now that you know about Newton’s first law of motion, how might you use it to ride a skateboard more safely?
      ::既然你知道牛顿的第一部运动法, 如何用它更安全地骑滑板?