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When you want to know if something is transparent to visible light or not, here is the mystery material and here is visible light.
而我们知道,物体是否对可见光透明，这里是神秘的材料，这里是可见光。
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On this guy, I have 10 from the left 10 acting this way, 4 acting that way.
对这个物体,受到一个 10 牛的从左向右的力,10牛的力朝这边,4牛的力朝那边
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There is work due to gravity.
我们就说对这个物体做了功。
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Well, yes, of course things fall down, but why?
对，物体当然下降，但为什么？
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So, hopefully that kind of clears up that question. And, of course, when the velocity actually is zero, this equation that the de Broglie has put forth is valid for anything that has momentum, so if something does not have any velocity at all, it actually does not have momentum, so you can't apply that equation anyway.
能回答你的问题，当然，如果速度真的是零的话,德布罗意提出的这个方程,只对有动量的物体成立,所以如果一个东西没有速度，它没有动量，也就不能应用这个方程。
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If in a typical control the red parts of the brain respond when somebody is looking at a face and the blue parts that you see here respond to some other objects that are essentially matched for.
在典型的控制组中,当被试看到一张人脸后,大脑的红色部分会作出反应，看到其他物体的时候,大家在此看到的蓝色部分,对基本上对应的事物做出反应。
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If all you know is the particle is falling under the affect of gravity, that's not enough to say where the particle is, right?
如果你只知道,质点受重力作用下落,那并不足以表明物体的位移,对吧
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Other is gravitational mass, which is the measure of how much you're attracted to the Earth.
另一个是引力质量,它可以用来衡量地球对物体引力的大小
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Imagine then from now on, we can find the mass of any object, right?
假设从现在开始,我们就能测量任何物体的质量了,对吧
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It's not talking about the gravitational pull of the Earth on an object.
没提到地球对物体的引力
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Here is some object, it's 5 kilograms and I apply 10 Newtons.
这有一个物体,5 千克,我对它施加 10 牛的力
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This is the force exerted by the spring on the mass.
这是弹簧对物体的作用力
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You cannot tell the mass, because what you are doing now is appealing to the notion of mass as something that's related to the pull of the Earth on the object.
你无法测出质量,因为你现在所做的是把质量,用地球对物体的引力给替代了
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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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We are constantly looking for values of F and we're constantly looking for responses or bodies to a known force.
我们不断地寻找 F 的值,我们不断地探索已知力对物体的作用
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the ropes will be pulling the block with T in the other direction, then I got 10 Newtons here.
绳子也会对另一物体施加方向相反的拉力 T,于是我知道这里是 10 牛顿
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Consequently, for this object the position y, at any time t is known to be 15+10t-5t^.
因此,对这个物体来说,在任意时刻的位移y,就应该为15+10t-5t^
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For this guy, F = ma will be 10 - f = 3a.
对这个物体,F = ma 就是 10 - f = 3a
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Now, you can do F = ma for the three different objects.
现在你可以用 F = ma 对这三个物体进行计算
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Then we do F = ma for these two guys.
然后我们对这两个物体使用 F = ma
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I know this is the right answer, because if I now find the acceleration, I find it's mg divided by m and I get -g as the answer for all bodies.
我知道这个等式是正确的,因为现在如果我要求物体的加速度,用 mg 除以 m,我就得到 -g,这个结果对所有物体都成立
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The free-body diagram, it says you can pick any one body that you like and apply F = ma to it, provided you identify all the forces acting on that body.
所谓隔离法,就是说你可以任意 选取一个物体,分析出它所受的所有力后,单独对其运用 F = ma 进行计算
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Then, to find the meaning of b, we take one derivative of this, dx/dt, that's velocity as a function of time, and if you took the derivative of this guy, you will find as at+b. That's the velocity of the object.
接下来,为了弄清b的含义,我们取它的一阶导数,dx/dt,得到速度作为时间的函数,如果你对它求导的话,你会得到at+b,这就是物体的速度
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