For example, no matter how much a dancer wishes to leap off the floor and then start turning, the law of conservation of angular momentum absolutely prevents such a movement.
例如，无论一个舞者多么想要跳离地板，然后开始旋转，角动量守恒定律绝对阻止这样的动作。
有了旋转的角动量。
That's a spin angular momentum.
那是旋转的角动量。
Look at that spin angular momentum.
观察那个旋转角动量。
Why? Because it has angular momentum.
为什么，因为有了一个角动量。
Angular momentum is in this direction.
角动量是这个方向了。
What will the spin angular momentum do?
旋转的角动量会怎样呢？
What will the angular momentum vector do?
角动量的矢量会怎样呢？
Angular momentum is now in this direction.
角动量现在是在这个方向。
And what does the spin angular momentum do?
旋转的角动量怎么了呢？
What is the magnitude of that angular momentum?
角动量的，数值是多少？
It describes the angular momentum of the electron.
它描述的是，电子的叫角动量。
We have here the spin angular momentum that you saw.
这有一个旋转的角动量,如你们所见。
You give it spin angular momentum, it becomes stable.
有了一个旋转的角动量，就变得稳定。
Spin angular momentum will start to chase the torque.
旋转的角动量会开始，跟随那个力。
I've changed the direction of the spin angular momentum.
我改变了旋转角动量，的方向。
Angular momentum is pointing straight at me, away from you.
角动量直接指向我，远离你们的方向。
The angular momentum change must be torque t times delta t.
角动量的改变就是,力乘以δ
I add angular momentum in this direction and you see that here.
我在这个方向加入了角动量，你们可以在这看到。
So spin angular momentum has the property of stabilizing things.
旋转的角动量有，稳定事物的性质。
Somehow, it has the smell of some conservation of angular momentum.
不知怎么的，这一定律和,角动量守恒定律有所相似。
That means if there's torque, there's a change of angular momentum.
这意味着，如果那有一个力矩，就会有角动量的改变。
Bohr says that the energy is quantized through its angular momentum.
波尔说能量通过角动量，被量子化。
And now the angular momentum is rotating like this, is pointing here.
现在的角动量是像这样，转动的，指向这。
That's immediate consequence of the conservation of angular momentum.
这是角动量守恒的，立竿见影的效果。
And so the angular momentum of spin of the wheel is in this direction.
所以旋转的角动量是，这个方向。
But notice that l, the spin angular momentum, has moved from here to here.
注意l，旋转的角动量，已经从这移到了这。
I'm going to spin it with a high angular momentum, high spin angular momentum.
以高的角动量来旋转，高旋转的角动量。
Angular momentum is conserved about this point Q, but only about that point Q.
角动量，在点Q守恒，也只有在点Q守恒。
Therefore there is a total angular momentum which is the vectorial sum of the two.
因此，总的角动量,有两个向量。
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