单词tennis ball
un.: 网球
网球
So, try to see that the tennis ball is very close to an ideal parabola.
所以，试着看，网球是一个，比较理想的抛物线。
A racket bounces a tennis ball up and down on the court , before a hand grabs the ball.
球场上，一只球拍啪啪啪弹着球，接着，一只手抓住了球。
So the top curve shows the body weight of a genetically obese mouse that eats nonstop, until it turns fat like this furry tennis ball.
上面的曲线显示体重是一个有肥胖基因的老鼠不停的吃，直至它变得象这个毛茸茸的网球一样胖。
With a tennis ball under your hitting arm, you"ll be forced to hold the racquet out in front of you and use proper technique.
夹一个网球在你击球胳膊的腋下，会强迫你保持拍头在你体前并使用更合理的技术。
Your peripheral vision may not be all that good for watching a fast moving table tennis ball onto a relatively small racket head.
你的余光也未必那么好，能看着一些如此快速运动的小乒乓球到达一个相对较小的拍头上。
You want to have completed your cross step and be back in the side shuffle before your opponent hits the tennis ball.
但你需要在对手击球前完成交叉步并使用侧滑步。
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。
a tennis ball in class like this, then the whole trajectory is. . . the whole trajectory is in one plane in the vertical plane.
如果我抛出一个网球，这样，那么整个轨。，在一个平面上，一个垂直平面上。
To see why this happens, imagine throwing a tennis ball into the air.
要知道为什么会发生这种情况，请想像一下往空中扔网球的情景。
Here"s a simple tip that will help you master this shot: Practice hitting low volleys with a tennis ball placed under your hitting arm.
这里有一个小窍门帮助你掌握这种击球方法：夹一个网球在你击球胳膊的腋下来练习低位截击。