He spent hours throwing a tennis ball against a wall

他好几个小时都对着一堵墙掷 网球 。

Not completely elastic but not bad . A tennis ball & not completely elastic but not bad .

不是完全弹性的，但不坏，一个 网球，-不是完全弹性的，但不坏。

Like to flute and Xiao playing to be interested in tennis ball and ballet .

爱好长笛和箫演奏，喜欢 网球和芭蕾舞。

An automatic table tennis ball server is designed by using infra-red sensor and a few electric devices .

利用红外光传感器和较少的电子器件，设计了一种 乒乓 球全自动供 球器。

A hard return hitting the tennis ball above your head .

在你的头顶上用力地 击球。

The act of hitting a tennis ball with a tennis racket .

（双打）抢打同伴的 球用网球拍打 网球的动作。

The impact of the tennis ball really stung his leg .

网球撞击在他的腿上，真够疼的。

While out one morning in the park a jogger found a brand new tennis ball and seeing nobody around he slipped it into the pocket of his shorts .

一天早晨在公园里，一个慢跑者发现了一个全新的 网球。看到周围没有人，他就把它顺进了自己的短裤口袋。

All the kinetic energy is in the tennis ball ; nothing is in the wall .

也就是 网球的动能；，墙壁没有动能。

We have here a trajectory of a golf ball or a tennis ball in26.100 .

假设这是一条属于教室里，某 高尔夫球或 网球的运行轨迹。

So look at the tennis ball first .

首先，看 网球。

This tennis ball has no more bounce .

这个 网球已经失去弹力了。

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 soft return so that the tennis ball drops abruptly after crossing the net .

当 球过网后进行一个轻的回击以致 球可以突然落下。

From Art Dept of Chifeng normal special school study flute and like vocality table tennis ball .

来自赤峰师专艺术系，专业学习长笛。爱好声乐和 乒乓 球。

I have a tennis ball .

我有一个 网球。

I have here a tennis ball and I can bounce this tennis ball I can throw it down .

我这里有个 网球，要是把它对着地面扔，它会弹起来。

The utility model relates to a three-purpose tennis ball .

本实用新型涉及三用 网球。

A lump the size of a tennis ball .

与 网球一样大小的肿块。

He couldn 't throw a tennis ball .

他不能举办一场 网 球赛。

She just tipped the ball over the net . The tennis Ball was hit Back and forth .

她刚好把球击过网. 网球被来回地击打。

He hit the tennis ball over the net .

他把 网球 打过了网。

If you can catch a tennis ball with your hand you can learn volley easily .

假设您能用手 接球，您就能轻易学会截击。

There is air drag on that tennis ball .

网球受到空气阻力。

To make a tennis ball spin forward the racquet must be moving from low to high at contact .

为了要使 网球 球旋转向前，网拍一定要在接触点从低到高移动。

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 tennis ball is hollow but a base ball is solid .

网球是空心的，但棒球是实心的。

Why the table tennis ball swings back and forth when nobody plays it ?

没有人挥动球拍，为什么 乒乓 球会自己来回摆动？

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。