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Now, gravity, well force, is equal to mass times acceleration, g and the acceleration due to gravity is g.
是重力，等于质量乘以加速度，由重力导致的加速度是。
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And the idea was that gravity did work on the water and falling, and that work led to the generation of heat.
焦耳的想法是,重力对水，做了功。
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When the charge is applied, if the upper plate is negative, we would expect that the negative droplet would be repelled at a rate exceeding the gravitational fall.
当电荷起作用时，如果上边的板子是负电的，我们可以期待负电的液滴会,超过重力下降速度的速度被排斥。
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But gravity has a remarkable property that the pull of the Earth is itself proportional to the inertia of the object.
重力有一个显著特征,即地球的引力,与物体的质量成比例
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They seem to be going somewhere and there's this sort of force of pull or gravity in music having to do with some chords wanting to go to other chords.
和弦向某一个方向发展，就像有一股力量拉着它们,或者说音乐的重力吸引着它们，让一些和弦想行进成为另一些和弦。
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One should do," he says, "what archers do when attempting to reach a distant target, namely, aim your bow high, knowing that the force of gravity " will bring the arrow down."
他说：，“一个人应该做的是，模仿伟人所为,当试图达致遥不可及的目标时，意即将目标设高，明了重力会将,射出的箭吸回地面“
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We live in a gravitational field and that it affects our day to day life, and if you have hip pain or a hip that's diseased in some way, and you can't stand up against that gravitational field in the same way, that severely limits what you can do in the world.
我们生活在一个重力场中,这个场影响着我们的日常生活,如果你的髋关节疼痛,或者有其他髋关节疾病的话,就不能像平常一样,站在这个重力场中了,这严重限制了人的活动能力
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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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You might be winded doing it the second way, but when you get to the top and you are at the 60th story your gravitational potential is independent of how you got there.
对于走路你可能很抓狂，但你一旦到了顶层,你就是在第60层,你的重力势能,与你如何到达那里无关。
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You know, if you want to measure the potential energy of something in a gravitational field, you have to define the zero somewhere, right, because it's arbitrary. You can set it anywhere you want. It's the same with enthalpy.
你知道，如果你想测量重力场,中某种东西的势能，你需要，在某处定义一个零点，对吧？,因为势能的值是任意的,你可以把它设定在。
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By the way, when I say there's 10 Newtons acting this way, you might say, "What about gravity? What about the table?"
顺便提一下我说有 10 牛的作用力,你也许会问,"那重力呢,桌子对它的力呢"
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Whether you take the elevator to the top of the Hancock Tower or whether you walk up the stairs, the change in gravitational potential is identical.
不管你是乘电梯,去大厦的顶层,或者是步行，重力势能的变化是相同的。
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We all know that in a falling elevator, you definitely do not escape the pull of gravity.
我们都知道在一个下坠的电梯里,你当然还是会受到重力的
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This also tells you that the mass of an object has nothing to do with gravitation.
这也表明,物体的质量与重力无关
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Imagine that this is in outer space where there is no gravity for now.
就假设现在这是在没有重力的外太空
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So, you will feel weightless for a short time or you'll feel your weight is little.
所以你会短时间的感觉到无重力,或者感到自己变轻了
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If all you know is the particle is falling under the affect of gravity, that's not enough to say where the particle is, right?
如果你只知道,质点受重力作用下落,那并不足以表明物体的位移,对吧
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For example, let's take the case where the particle is falling under gravity.
比如说,举个例子,一个质点正在重力的作用下下落
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You feel heavy and it reads more because the poor spring not only has to support you from falling through the floor, but also accelerate you counter to what gravity wants to do.
你感到自己变重以及读数增加,因为现在弹簧不仅要支撑你,不让你掉下来,还要抵消重力的作用让你加速
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You don't feel any weight because your weight is the opposition you get to falling through the floor; but if the floor is giving way and you're just falling freely, you feel weightless.
你不会感到重力,是因为你的重力在阻碍你穿过地板,如果没有地板,你自由下落,也感觉不到重力
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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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So，the point is,every object falling under gravity is given by the same formula, but there are many, many objects that can have many histories, all falling under gravity, and what's different from one object and the other object is, when was it dropped, from what height, and with what initial speed.
关键是,每一个受重力作用下落的物体,都有同样的表达式,但是各个受重力作用下落的物体,都有不同的初始条件,所以它们的区别在于,下落时刻,下落高度和初始速度
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By the way, that's a very remarkable property of the gravitational force-- the cancellation of the two ms.
顺便说一下,这是重力的一个重要属性,即可以消去等式两边的 m
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You are pushing down with the weight mg, and the floor has got to be pushing up with the mg, because the spring is not going anywhere.
你向下的作用力是重力 mg,然后地面向上的支持力也是 mg,因为弹簧现在根本没动
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You can see that if a was equal to g, your downward acceleration is that of gravity, namely the cable has snapped in the elevator, Then you don't feel any weight.
你会发现如果 a 等于 g,你下降的加速度就是重力加速度,也就是电梯的绳索断了,那时你会完全失重
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For example, suppose you use vertical motion and you use y instead of x; and a would be g or -g; that's a particle falling down under the affect of gravity.
例如,假设在竖直运动中,你用 y 来代替 x,那么 a 就是 g 或者 -g,这就是一个受重力作用下落的质点
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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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For most of us, gravity acts this way, defines a vertical direction very naturally and the blackboard is oriented this way, so very natural to call that x and call that y and line up our axes.
对我们多数人来说,重力作用下,很自然地确定了竖直方向,而我们的黑板又是这个指向的,所以很自然地定出 x 轴和 y 轴,并标出我们的坐标系
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So, we know in this example the initial height should be 15 meters and the initial velocity should be 10, and for acceleration, I'm going to use -g and to keep life simple, I'm going to call it -10.
我们知道在这个例子中,初始高度为15米,初始速度为10,然后是加速度,我们用"-g"表示重力加速度,为了计算方便,加速度的值取为-10
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Conversely, if you get an answer and it doesn't seem to make sense, then you've got to go back and ask, am I violating some of the assumptions, and here you will find the assumption that the particle had that acceleration a is true as long it's freely falling under gravity but not when you hit the ground.
反过来说,如果你得到一个结果,发现似乎是错的,那么你就应该回过头来问问自己,我是不是违反某些前提了,这个模型中,你就发现,只要质点在重力作用下自由下落,质点具有加速度a的前提是正确的,但是落地后就不成立了
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