在物理学中，运动的物体有两个特征与理解能量系统动力学相关：惯性和动量。
In physics, moving objects have two characteristics relevant to understanding the dynamics of energy systems: inertia and momentum.
一个重物有很大的动量，也就是说，比如一位高速移动的足球运动员一旦运动起来，就很难改变运动状态。
A heavy object, like a football player moving at a high speed, has a lot of momentum—that is, once he is moving, it is hard to change his state of motion.
运动量少、与同伴聚会少、阅读印刷媒体（即报纸）少都与幸福感较低有关，但令人惊奇的是，做作业的时间少也与幸福感较低相关。
Less sport, and fewer meetings with peers correlated with lower wellbeing, as did less time reading print media (newspapers) and, surprisingly, less time doing homework.
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