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That is, you minimize potential energy and you see things falling under the force of gravity and so forthgoing to potential energy minima in conformance with this result.
换句话说，你使得势能最小化,然后发现我们关注的东西,在重力或者其他力的作用下下落,直到势能最小的地方,这和我们刚才的结果是一致的。
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There are many kinds of work. There's electrical work, take the motor, you plug it into the wall, electricity makes the fan go around, that's electrical work. There's magnetic work.
我们复习一下大一,学过的功的概念：,物体在力的作用下，运动了一段距离。
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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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We know what an electric field is, it's just a space through which a Coulomb force operates.
我们知道，电场不过,是库仑力的作用空间。
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And there are various forces that play in the nucleus that will dictate when this will be stable and when it won't be.They isolated it, but it decays very quickly on the order of microseconds Lifetime on the order of microseconds.
在原子核中有很多种力,都会产生作用，当条件是稳定的,还有当它不是的时候，它们提取出来，但是它会以微秒的速度衰变,生命只有几微秒长。
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We focus on one because we are paying for it, but the wall is doing the opposite.
我们只关注某一边因为我们只对这一边施力,但是墙对另一边有反向的作用力
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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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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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Mass of an object is how much it hates to accelerate in response to a force.
物体的质量,反映了物体在力的作用下加速的难易程度
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He just said whenever there's an acceleration, it's going to be due to some forces and it's your job to find what the forces are.
他只说过只要有加速度,就说明有力的作用,你们的任务是要找出这些力
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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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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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If you look at the electrical force, the force of electricity, proton and electron or something, it's not proportional to the mass of either object.
如果你考察电作用力,即电现象产生的力,质子啊,电子啊,或者其它什么东西,这种力不和物体的质量成比例
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you're looking for that equal and opposite forces acting at two ends of the rope.
你就得求出作用在绳子两端的,大小相等方向相反的力
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It plays a big role in gravitation, in the Coulomb interaction.
它在引力和库仑力中都起着重要的作用
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The fact that you don't need a force for it to move forever at a given speed in a given direction, that's not obvious, because in daily life you don't see that.
对于物体不需要力的作用就能保持,确定的速度和方向持续运动这一事实,它并非显而易见,因为在日常生活中你看不到这种情况
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So, we just talked about the force law to describe the interaction between a proton and an electron. You told me that when the distance went to infinity, the force went to zero. What happens instead when the distance goes to zero? What happens to the force?
我们刚刚讨论了描述质子,和电子之间相互作用力的定律,当距离变为无穷时,力变为零，那当距离变为,零时会发生什么？,这时候力是多少？
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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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Whenever there is a force, it can be traced back to a tangible material cause, which is all the time a force of contact, with the exception of gravity.
如果有作用力,那它一定能找到一个明确的实体施力物体,也就是无论何时物体受的都是接触力,引力除外
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There are forces between the quarks.
在夸克之间存在力的作用
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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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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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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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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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That's how by either balancing the unknown force with a known force or by simply measuring the acceleration as I fall towards this podium and multiplying by mass, you can find the force that exerts on me.
我们既可以让未知力与已知力平衡,也可以只测量我冲向讲台时加速度的大小,再与我的质量相乘,都能求出作用在我身上的力的大小
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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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We are constantly looking for values of F and we're constantly looking for responses or bodies to a known force.
我们不断地寻找 F 的值,我们不断地探索已知力对物体的作用
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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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The only force acting on this guy is this little f.
这个物体只受一个力的作用,也就是 f
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