It means this tennis ball... while it is in free fall, it has no weight.
再比如说这个网球。，自由落体过程中它没有重量。
2
The cons hurry for cover and watch the bars pull free from the window – the weight of the elevator blows them off easily.
团伙们匆忙地找东西垫在地上，他们看着栅栏被从窗户上拉下来-电梯的重量轻松地就将它们扯动了。
3
"Findings from this study suggest that this incentivized structured weight loss program with free prepared meals can effectively promote weight loss compared with usual care group," the authors said.