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No, we call that work positive work. All right, so that means we need to put a negative sign right here, by convention.
历史上有过不同的习惯，这里我们规定,如果环境对系统做功。
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You'll also know that all of these binding energies here are negative, so the negative sign indicates that it's low.
你们将会知道所有的这些,结合能都是负的。
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And I've reversed the fraction here because of the negative sign here.
我交换了分子和分母,因为这里有个负号。
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It says, if you pull it to the right, so that x is positive, the spring will exert a force which is in the negative direction; that's why you have a minus sign.
就是说,如果你向右拉,x 取正值,弹簧产生的力方向为负,这就是这里用负号的原因
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Another way to say that it's going to be less, so you don't get confused with that the fact this is in the numerator here, there is that negative sign so it's less energy but it's a bigger negative number that gives us that less energy there.
另一个方式去说它将会变得很低实用，你们不用在这里的计算器的事实感到迷惑,这里有一个负号实用，它是更少的能量,但它是一个更大的数字,这里了它给了我们更少的能量。
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Infinity is the force when we're thinking about it and our brains, negative infinity is when we actually plug it into the equation here, and the reason is the convention that the negative sign is just telling us the direction that the force is coming together instead of pushing apart.
说力有多大时，我们想到的,是无穷大，而方程解出来的,是负无穷，这是因为习惯上,我们用负号表示力的方向,是相互吸引而不是相互排斥的,所以我们可以用库仑定律。
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Convention, OK, this negative sign is just a pure convention. You just got to use it all the time. If you use an old textbook, written when I was taking thermodynamics, they have the opposite convention, and it's very confusing. But now we've all agreed on this convention, and work is going to be with the negative sign here.
系统对外界做功的符号为负,这就是我们,在本课中的规定，纯粹出于统一符号的需要，有些教科书中，可能会使用相反的符号规定,注意不要混淆了，这门课上,我们将一直使用。
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Remember, you've got to keep track of the sign of acceleration, so if you're picking up speed towards the ground, a is negative, so it will be g plus a, but a is a negative number.
记住,一定要注意加速度的符号,所以当你加速下降的时候,a 是负的,还是 g 加上 a,但是 a 是负数
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