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That means the force you're applying is cancelled by another force, which has got to be the force of friction.
意味着你施加在物体上的力被另一个力抵消了,这个力就是摩擦力
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There, Newton doesn't tell you what forces are going to be acting on a body in a given situation.
在式子里,牛顿没有告诉你,在给定条件下,有哪些力,作用在物体上
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So, if we think about the force that occurs between a positively and a negatively charged particle, what we have is essentially a Coulomb force, so we can describe this as a force of attraction.
一个带负电的粒子之间，的作用力,这本质上就是库伦力，我们可以把它，描述成一个引力。
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It's not doing as much work.
活塞上的力。
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In every context in which I place a body, I'll have to know what are the forces acting on it.
每次我拿一个物体举例子时,我就得知道有哪些力作用在物体上
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It's the 10 Newtons acting on it, because I know the 10 Newton is pushing me and I'm going to feel it even if I'm here.
他们认为这 10 牛的力作用在了物体上,因为这个力在推着物体前进,物体能感觉到的,即使没有直接接触
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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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The physicist has to constantly find out what forces act on bodies.
物理学家必须,不断地寻找都有哪些力作用在物体上
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The stuff that people tend to add sometimes is to keep drawing the 10 Newtons that's acting on that.
有人经常凭空添加的力,总是把这个 10 牛的力硬加在这个物体上
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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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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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You've got many forces acting on a body.
很多力同时作用在物体上
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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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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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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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Your problem is to only look at the forces of contact on you, and that is just this f.
你只需要注意那些直接作用在这个物体上的力,那就只有 f 了
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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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Then I know that kx is equal to the force that is exerting at this separation.
然后我就能知道 kx 等于,这个位置上讲台产生的力的大小
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