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So, a massless body cannot have a net force on it, because the acceleration of the rope cannot be infinite.
所以没有质量的物体不会受到力,因为绳子的加速度不可能是无穷大
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In fact, it has to be some finite number, which is the acceleration of either of these two guys.
事实上它必须是有限的数值,也就是这两个物体某中某一个的加速度
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And, you know acceleration means either change of speed or change of direction.
你知道加速度意味着,不是改变速度就是改变方向。
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The government has liberized the economy and that has of course been playing a role but the growth acceleration started almost a decade before that, so the factors are a little more complex.
印度政府让经济自由发展,这一决策显然是起了作用的,但在这一决策出现约10年前,印度经济的加速发展便开始了,所以经济腾飞的原因还比较复杂。
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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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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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Then, I bring the elephant and I pull the spring by the same amount and I find the acceleration of the elephant and the denominator is obviously the mass of the elephant.
然后我再找来大象,用相同的力去拉弹簧,大象就具有了加速度,很明显,分母就是大象的质量
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First one says, if you knew the force acting on any body, without going into what caused the force, then you may set that force equal the mass times acceleration of the body.
第一部分是,如果你知道作用在任一物体上的力,无论这个力的来源是什么,都可以令力等于质量乘以物体的加速度
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If your plan is to accelerate a 3 kg mass with an acceleration of 2 meters per second, you better have a rope that can furnish that force and it can take the tension of 6 Newtons.
如果你想用 2 米每秒平方的加速度,去拉一个 3 千克的物体,那么你就需要一根能提供拉力的绳子,并且它能够承受 6 牛的张力
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When you're falling to the surface of the Earth, you are describing a problem of constant acceleration.
当你讨论下落问题时,你在描述一个加速度恒定的问题
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It's useful to have the average acceleration, which you can find by taking similar differences of velocities.
平均加速度也是很有用的,你可以用类似方法,取速度的变化量求出来
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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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It knows that this particle happened to have a height of 15, at the time of 0, and a velocity of 10, and it is falling under gravity with an acceleration of -10.
这个质点恰好处在高度为15的地方,零时刻,初速为10,并在重力作用下以-10的加速度下坠
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Then the acceleration of the planet is the force of gravity between the planet and the Sun, which Newton will tell you is directed towards the Sun and it depends on how far you are.
行星的加速度源自,行星和太阳之间的作用力,牛顿认为这个力指向太阳,它的大小取决于行星离太阳有多远
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Therefore, when you divide by the mass to get the acceleration, the response of different bodies is inverse to the mass.
因此,当你拿力除以质量得到加速度时,不同物体的加速度与质量成反比
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But the acceleration it produces on the elephant and on the mass, are in an inverse ratio of their masses.
但这个力使大象和物体产生的加速度,与它们的质量成反比
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It says that, "If a body has an acceleration, then you need a force and the relation of the force to acceleration is this thing."
它是这么说的,"如果一个物体有加速度,那么你需要有一个力,力和加速度的关系是这样的"
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A limited class of problems is one in which the acceleration is just a constant.
在这类有限的问题里,加速度均为常数
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Acceleration is the easiest thing to measure of these three quantities.
加速度是这三个量中,最容易测量的
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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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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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We can be precise about how much bigger by saying, "If the acceleration of a body to a given force is ten times that of a one kilogram mass, then this mass is one-tenth of one kilogram."
我们能精确地知道质量能大多少,只需要说,"如果物体在给定力作用下的加速度,是一个 1 千克物体的加速度的 10 倍,那这个物体的质量就是 1 千克的十分之一"
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But it has an acceleration of -g.
但是有加速度 -g
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Why should the amount by which you're attracted to the Earth be also a measure of how much you hate acceleration?
为什么物体受地球引力的大小,恰好能衡量物体加速的难易程度呢
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Take the difference of the two velocities and divide by the difference of the two times, and you've got the acceleration.
求出速度的差值,除以时间的差值,这样就能得到加速度
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The advantage of introducing that guy is that if you like, I can now write an equation for the acceleration as a vector.
引入它的好处是,如果你愿意的话,我可以把加速度写成矢量形式
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