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Occasionally, you'll find you need to cancel out units, because, of course, you're always doing unit analysis as you solve your problems, and sometimes you'll need to convert joules to kilogram meters square per second squared.
偶然地，你会发现需要消除单位，因为在解题时,经常要做单位分析，所以有时候需要把,焦耳换做,一千克乘以米的平方除以秒的平方。
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Again, your common sense tells you, "Look, you are pulling something whose effective mass seems to be 5, the answer is 2."
你的常识会又一次告诉你,"你在拉一个相当于 5 千克的物体,所以加速度是 2 "
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The seconds cross out, the kilograms cross out, one of the meters crosses out from the top, so we're left with an answer in meters.
秒消掉了，千克消掉了，单位米和上面的一起约去了，所以我们得到的答案只剩下米。
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0 And it has a mass of 9.11 times 10 to the minus 31 kilograms The charge compensation comes out of the nucleus with the proton and it is positive 1.6 times 10 to the minus 19 coulombs.
它的质量是9。11乘以0,到负31千克,电荷补偿来自于,有质子的原子核,它是+1。6*10^库伦。
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A kilocalorie, and this is really what we--when people talk about calories, how many calories in food, it's really kilocalories that they're referring to, but that would be the energy required to raise a kilogram of water one degree centigrade.
一千卡,是人们讨论卡路时是真正用的单位,当提起食物中的热量,人们指的是多少千卡,一千卡,是将一千克水提升1℃所需要的热量
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Likewise for mass, we will take a chunk of some material and we will call it a kilogram.
质量也是这样,我们找来一大块材料,然后称它为 1 千克
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Here I got 3 kg and I got 2 kg and I'm pushing with 10 Newtons and I want to know what happens.
一个物体 3 千克,另一个 2 千克,现在我用 10 牛的力推它,我想知道接下来会怎样
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I'm going to give you a glass case and in the glass case is an entity with this as one kilogram, by definition.
我给你一个玻璃箱,箱子里放的东西刚好是 1 千克,这是根据定义的
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If I pull the one kilogram mass and I let it go, it does something, some acceleration.
如果我拉 1 千克重的物体并松手,就会获得一个加速度
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Most of chemistry has gone SI so every mass should be in kilograms.
大部分的化学遵守国际单位制,所以质量的单位应该是千克。
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A joule is a kilogram meter squared per second squared.
一个焦耳等于,一千克乘以米的平方除以秒的平方。
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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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So, the way to measure force is in kilogram meters per second squared.
所以,力的单位是千克米每秒平方
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Now, I tie this one kilogram mass to it and let it go.
现在,我把这个 1 千克重的物体系上,并松开手
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Newtons acting on 2 kg, gives you an acceleration of 2.
牛的力作用在 2 千克的物体上,那么其加速度大小就是 2
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The point is, the one kilogram is a matter of convention.
关键在于,1 千克已经定下来了
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How do we know the mass of this is 5 kilograms?
我们怎么知道质量就是 5 千克呢
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But this is the acceleration of the one kilogram mass.
但这是 1 千克物体具有的加速度
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We divide that by the mass, so 0.12 kilograms, that's the mass of a regulation baseball for the major leagues, and the velocity of the baseball is 42 meters per second. So, we can cross out our units doing our unit analysis.
我们用质量来除它，质量为0，12千克，这是大多数联赛规定的棒球质量,棒球的速度为42米每秒,所以，我们可以消去单位,来做单位分析。
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That kilogram, I don't expect you to deduce.
那 1 千克,我没指望你们能推导出来
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Here's the body of mass 3.
这就是那个 3 千克的物体
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A typical problem that you may have done in your first pass at Newton's law, someone tells you a force of 36 Newtons is acting on a mass of whatever, 4 kilograms; what's the acceleration?
在你们第一次接触牛顿定律时,可能见过这么一道典型题目,告诉你,一个 36 牛的力,作用在一个物体上,4 千克吧,问加速度是多少
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Mass is measured in kilograms.
质量的单位是千克
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That is 6 Newtons divided by 3 kg is also an acceleration of 2.
即,6 牛除以 3 千克同样得到加速度是 2
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You hook one end of the spring to a wall and you pull it from rest by some amount and you attach the one kilogram mass to it.
你把弹簧的一端固定在墙上,然后拉伸一段距离,接着你把 1 千克物体固定在上面
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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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I got 2 kg and I pull this guy with 10 Newtons.
还有一个 2 千克的物体,我用 10 牛的力来拉它
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I got 3 kg and I have a rope.
有一个 3 千克的物体和一根绳子
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We'll first pick the body, with mass 3.
我们先来分析这个 3 千克的物体
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If you knew this was one kilogram, then the acceleration of the elephant, which will be some tiny number, maybe 100th of what this guy did; the mass of the elephant is then 100 kilograms.
如果已知这个物体的质量为 1 千克,那大象的加速度,会是一个比较小的数,可能是物体加速度的 1 / 100,大象的质量就是 100 千克
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