First, find where that real center-of-masspoint is in-game.
首先，找到游戏中真正的重心点位置。
2
Based on the Poisson bracket and the discriminant of integral of motion, we prove the problem that the moment of momentum is the integral of motion when the masspoint is affected by central force.
运用泊松括号，依据运动积分判别式，证明了质点受有心力作用时，其动量矩是运动积分的问题。
3
As mass production techniques were refined in the 19th century, the price of pianos dropped to the point that a larger proportion of the population could afford to own them.