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。

麻省理工公开课 - 热力学与动力学课程节选

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

耶鲁公开课 - 基础物理课程节选

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

耶鲁公开课 - 基础物理课程节选

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

耶鲁公开课 - 基础物理课程节选

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

耶鲁公开课 - 基础物理课程节选