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But Aristotle used to think that if you want something to move, there has to be some agency making it move.
但亚里士多德认为,如果要让物体运动,那就必须有某种作用让它运动
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I know that if the second mass moved faster than the first one, then the picture is completely wrong.
因为我知道如果第二个物体比第一个运动更快,那么受力图就肯定不是这样了
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There are many kinds of work. There's electrical work, take the motor, you plug it into the wall, electricity makes the fan go around, that's electrical work. There's magnetic work.
我们复习一下大一,学过的功的概念：,物体在力的作用下，运动了一段距离。
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But Galileo already managed to find examples where things would roll on for a very, very long time.
但伽利略已经成功找到了,物体可以运动很长很长时间的例子
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You simply want to describe things the way they are and then dynamics tells you how they changed and why they changed.
你只是单纯描述物体的实际状态,而动力学则是解释它们运动的方式和原因的
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So, for example, if you were trying to study the motion of some object, here is one example.
举个例子,如果你想研究某个物体的运动,这里有个例子
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Then next week we'll do more complicated problems that involve motion in higher dimensions, how to go to two dimensions or three dimensions.
下周我们将会处理更复杂的问题,包括更高维数的物体运动,如何处理二维以及三维运动
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Dynamics then tells you why the object goes up, why the object goes down and why is it pulled down and so on.
而动力学则会告诉你为什么物体向上运动,为什么向下运动,为什么停下来,等等
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The great discovery that Galileo and Newton made is that you don't need a force for a body to move at constant velocity.
伽利略和牛顿的伟大发现就是,物体不需要力来维持匀速运动
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But adding a constant velocity to objects does not change the fact that those which were maintaining constant velocity still maintain a constant velocity.
但是加上一个恒定速度并不会改变下述事实,即,那些正在匀速运动的物体,仍然保持匀速运动
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but you can sort of tell that the particle is moving slowly or rapidly by looking at the space in between these tick marks.
但你可以通过观察计时点之间的距离,来判断该物体运动的快慢
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It's very clear you don't need a force if something is doing nothing, just sitting there.
显而易见,如果物体没有运动,只是静止状态,那是不需要力的
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One way to say it is, every body will continue to remain in a state of rest or uniform motion in a straight line.
另外一种说法是,任何物体都会继续保持静止,或匀速直线运动的状态
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And know intuitively that if they move together, they will behave like an object of mass 5 and the acceleration will again be 2.
凭直觉认为既然它们一起运动,那么它们就相当于一个质量为 5 千克的物体,然后我们可以算出加速度为 2
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But if I see you through the glass, the object is going on some trajectory, which has got both up and down and horizontal motion.
但是如果我透过窗户看到你,这个物体沿着某个轨迹运动,既有上下,也有水平方向的运动
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When a body is going around a circle, they say that's some centrifugal force acting.
如果一个物体做圆周运动,他们就说有离心力作用于这个物体
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If it moved slower than the first one, it means it's rammed into this one.
如果它运动的比第一个慢,那么它就会撞上这个物体
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Nowadays, if you go to outer space, you can check for yourself that if you throw something out, it just goes on forever without your intervention.
现如今,如果你去了外太空,你可以向外抛个物体试试,如果你不打断它,它就会一直运动下去
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One way is to just use your common sense and realize that if you push it this way, these two guys are going to move together.
第一种方法就是你可以通过常识感觉到,如果你这样推它,这两个物体会一起运动
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He said, take a spring to outer space and we'll hook up some objects to them and see how fast they move and do a comparison.
他说,把一个弹簧带到外太空,往上面挂物体,看看它们运动的快慢,并进行对比
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That means, if you are going in a plane and you throw something up in the air, it seems to be going up and down to you.
也就是说,如果你在飞机中,你向空中扔出一物体,它也许会相对于你上下运动
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What's your plan for measuring acceleration if some little thing is moving?
如果某个小物体在运动,你要如何测量加速度
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So here's the long ruler and here's this thing moving.
这里有把很长的尺子,而这里有个物体在运动
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The reason it comes down is gravity is pulling it.
物体向下运动是因为重力作用
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You send something, you'll find it goes on forever.
向外抛一个物体,它就会一直运动下去
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We are moving at constant velocity.
我们现在是让物体匀速运动
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Here's a body that's moving, right?
这里有个物体在运动,对吧
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The particle is moving along this arc.
物体沿着这条曲线运动
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Everything moves around in 3D.
所有的物体在三维中运动
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What's this particle doing?
这个物体运动状态如何
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