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"Within that week with support, of the body weight support, we were able to get him to stand without any help at the legs so he was generating enough force to bear his body weight."
VOA: special.2011.06.01
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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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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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The chief minister's body was found by the Indian Air Force at the site where his helicopter crashed Wednesday.
VOA: standard.2009.09.03
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Gravity is one force that acts on a body without the source of the force actually touching it.
引力是一种受力物体收到了力的作用,但却没有接触施力物体的力
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Every force, with one exception, can be seen as a force due to direct contact with the body.
除了一个例外,其它所有力必须要和物体有直接接触
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The great discovery that Galileo and Newton made is that you don't need a force for a body to move at constant velocity.
伽利略和牛顿的伟大发现就是,物体不需要力来维持匀速运动
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Every time you are finding out a different force that's acting on a body with different origin.
每次你都会发现不同来源的力,作用在物体上
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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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When a body is going around a circle, they say that's some centrifugal force acting.
如果一个物体做圆周运动,他们就说有离心力作用于这个物体
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If you leave the body alone, maybe there's no force acting on it.
如果你把物体丢在一边,可能就没有外力作用在它上面
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One says, leave any body near the Earth, it yields a force.
有人说,在地球表面的任何物体,都会受到力的作用
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But do you know what the force on the body is?
但你知道物体受到了多大力的作用吗
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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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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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I've got to find them by experimenting, by putting other bodies and seeing how they react and then finding out what's the force that acts on a body when it's placed in this or that situation.
我得通过实验找出这些力,我会增加其它物体,观察其反应,求出当它处在这种或者那种情况下时,作用在物体上的力
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In fact, there's a property of gravitational fields anywhere, even in outer space, but there is some residual field between all the planets and all the stars in the universe, that the force on a body is proportional to the mass of the body.
实际上,这是任何地方的引力场都具备的属性,甚至是在外太空,在所有的行星和恒星之间,存在着某种剩余场,在这个场里作用在物体上的力,和物体的质量之间存在比例关系
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What makes the law surprising is that if I only gave you half the law, namely every body will remain at rest if it's not acted upon by a force, you will say, "That's fine. I accept that, because here's something, you leave it there, it doesn't move.
这条定律妙就妙在,如果只看定律的前半段,即,如果物体不受外力作用,将保持静止状态,你肯定会觉得,"这没什么,我能理解,因为你把一个物体放在那里,自己肯定不会动
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F = ma is universally true, independent of the nature of the force acting on a body.
= ma 是一条普适定律,与作用在物体上的力的属性无关
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If you bring a plus charge near a plus charge, if my body m, has a plus charge and another plus charge is there, it'll feel a force due to that.
如果让两个正电荷靠近,如果一个物体 m 带正电荷,在这里有另一个正电荷,它就会感受到力的作用
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For example, we know that if a body is near the surface of the Earth, the force of gravity of that object seems to be m times g, where g is 9.8.
例如,我们知道,如果在地球表面有一个物体,该物体受到的重力大小为 m 与 g 的乘积,g 等于 9.8
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FT means the total force on a body.
T 表示物体所受的合力
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