He spent hours throwing a tennis ball against a wall.

他花了数小时对着一堵墙扔网球。

My father would burst into the kitchen bouncing a tennis ball.

我父亲会拍打着网球闯进厨房。

I spent many hours mindlessly banging a tennis ball against the wall.

我花了好多个小时单调地对着墙打网球。

I have here a tennis ball.

我这里有个网球。

This tennis ball has no more bounce.

这个网球已经没有弹力了。

Last week a tennis ball hit me on the head, but I tried to ignore the pain, believing that it would go away sooner or later.

上周，一个网球击中了我的头，但我试图忽视疼痛，相信痛感迟早会消失的。

This is a table tennis ball.

这是一个乒乓球。

So, look at the tennis ball first.

首先，看网球。

There is air drag on that tennis ball.

网球受到空气阻力。

The largest is the size of a tennis ball.

最大一块有一个网球那么大。

We have here a trajectory of a golf ball or a tennis ball in 26.100.

假设这是一条属于教室里,某高尔夫球或网球的运行轨迹。

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。

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。

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。

Suppose I take a tennis ball 100 and I throw up a tennis ball in 26.100.

比如，我拿了个网球,把它向上抛26。

It's actually an advanced piece of robotics that won't fetch a tennis ball.

虽然它确实不会叼回抛出去的网球，但它可是一只先进的机器狗。

Or I see a chartreuse-yellow tennis ball on the lawn, pick it up and throw it.

否则我的目光会落到草坪上的淡黄绿色的网球上，捡起来，扔出去。

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。

He observed somebody hit a tennis ball and wondered about the paths of projectiles.

他看到别人打网球就会思考网球的行进路线。

I have also here a regular... well, it's not quite a tennis ball, but close enough.

这里有个规则的。，它接近于网球。

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。

The tennis ball-style single stack of balls in a tight-fitting cylinder is the simplest;

网球式的单层包装将圆柱体塞满是最简单的；

A fuzzy tennis ball flies faster than a bald one for the same reason, Mr Bottaro explains.

毛茸茸的网球比表面光滑的球飞得快的原因正是这个原理，波塔罗解释说。

It's a chunk of brain matter "roughly equivalent to a tennis ball in size," McAuliffe says.

“这是一大块的脑浆大致相当于一个网球的大小。”麦考利夫说。

Each "pebble" in a pebble-bed gas reactor is a graphite fuel sphere the size of a tennis ball.

在一个球形气体反应堆里的每一个“小球”都是一个网球大小的石墨燃料球。

(Think of what would happen if you tried to slow down a skateboard with a tennis ball on it).

试想一下，你用网球使滑板减速是什么效果。

The human brain has decreased by about the size of a tennis ball over the past 30,000 years.

——在过去三万年间，人类大脑的平均体积大小降低了百分之十。

The wall has an infinitely large mass, but the momentum of this tennis ball 2mv has changed by an amount 2 mv.

墙壁的质量无限大，但是网球的动量,改变了。

Procedural memory is your memory for skills, such as how to hit a tennis ball. This doesn't take conscious thought.

程序性记忆是对技能的记录，比如如何打网球，这并不需要意识过程。