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When we did the spring, we had this theory of Hooke's Law that told us something, and we built a simulation, or built some tools around that theory.
当我们写弹簧程序的时候,我们有胡克定律来告诉我们原理，然后我们建立了一个仿真模型，或者说是在这个理论基础上建立了一些工具。
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If you connect the body to a spring, which is neither compressed nor extended, there's no force acting on it.
如果将一个弹簧连在这个物体上,弹簧既没有被压缩也没有被拉伸,也不会有力作用在它上面
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With some degree of confidence, I'm working with a reliable spring and then I will get the mass of the elephant.
这时我就对弹簧有信心了,我用的是一个可靠的弹簧,我能测出大象的质量
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We know now with the same spring, by this comparison, we will find all objects now can be attributed a mass.
我们现在知道利用相同的弹簧,采用这种比较的方法,就会发现,所有物体都有确定的质量
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Newton is not going to come and tell you what force the spring will exert when it's pulled by some amount.
牛顿不会过来告诉你,弹簧被拉伸一定量时会产生多大的力
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Even in the case of this spring, when you pull it, if you pull it to the right by some force.
甚至是在这样的弹簧问题中,当你拉它的时候,如果你用力向右拉
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I draw a graph here of the amount by which I pull the spring versus the force it exerts.
我在这里画个图,纵轴是弹簧的拉伸量,横轴是力的大小
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You cannot have a spring pulled only at one side, because then it will then accelerate with infinite acceleration in that direction.
你不可能对弹簧只施加一边的拉力,因为那样的话弹簧就会以无穷大的加速度加速,就在这个方向上
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Now I can measure that, because I pull it by one centimeter and I find the acceleration it exerts on a known mass.
现在就能测量这个力了,因为把弹簧拉伸 1 厘米,我就知道它让一个质量已知的物体产生的加速度
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We want to know how much force it exerts when I pull it by a certain amount.
我们想知道当我们将弹簧拉伸一定量时,它能产生多大的力
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The spring is getting squashed because you are pushing down and the floor is pushing up.
弹簧现在被压缩了,因为你在往下压,地面在往上推
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We go back to the spring and we want to learn something about the spring.
我们回到弹簧的问题上来,我们要学习一些关于弹簧的知识
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Does outer space even rob you of something to which you can anchor a spring?
在外太空中你是否,不再能够固定住弹簧
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If every time I get the same acceleration, I'm convinced this is a reliable spring that is somehow producing the same force under the same condition.
如果每次都能得到相同的加速度,这个弹簧的可靠性就能令人信服,即它在相同的条件下能够产生相等的力
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It means, when you are accelerating upwards, as the elevator picks up speed, the reading on the spring will be more and you will feel heavy.
也就是说当你向上做加速运动时,就像电梯加速的时候,弹簧的读数会增大,你会觉得自己变重了
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I tie a spring to my back and I anchor it to the wall and see how much the spring stretches before the two forces balance.
我把弹簧一端系在背后,另一端固定在墙上,观察两个力平衡时弹簧的伸长量
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If it's positive, it means you've stretched it, if it's negative, it means compressed.
如果它为正值,就说明弹簧被拉伸了,如果它为负值,就说明弹簧被压缩了
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Therefore, what we have done now is, we can take all kinds of springs and we can calibrate the force they will exert under various conditions.
因此,我们现在能做到的就是,我们能处理各种各样的弹簧,我们能测出它们在不同的情况下,产生的力的大小
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He said, take a spring to outer space and we'll hook up some objects to them and see how fast they move and do a comparison.
他说,把一个弹簧带到外太空,往上面挂物体,看看它们运动的快慢,并进行对比
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Remember, when we hang the elephant in outer space, nothing is going to happen.
记住,如果我们在外太空悬挂一头大象,弹簧是不会有变化的
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So springs are always pushed or pulled on either side with the same force.
所以弹簧两边永远都是受到,相同的压力或拉力
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Namely, if you pull it by so much, that's the force it will exert.
也就是,将弹簧拉伸这么长,它产生的力就有这么大
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I move a little closer and I find the stretching is a different number.
我继续靠近讲台,发现弹簧伸长量有所变化
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First, we got to make sure the spring exerts a fixed force every time.
首先,要保证,弹簧每次产生的力是恒定的
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In the case of a spring, this is the law that you will deduce.
在弹簧这个例子里,这就是你推导出来的定律
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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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If you pull the spring, there is a force acting on it.
如果拉这个弹簧,就有力作用在物体上了
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So x is not really the coordinate of the end point.
其实并不是弹簧端点的坐标
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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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This is how masses can be tabulated using a spring.
这就是为什么能用弹簧测量物体质量
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