Gridiron physics: Scalars and vectors - Michelle Buchanan

Transcriber: Andrea McDonough Reviewer: Bedirhan Cinar

翻译人员: Yuyang Zhao 校对人员: Gabriella Hu

Fourth and nineteen, folks,

第四和十九，各位，

they've gotta have a play as time's ticking away

随着时间的流逝，他们赢了这场比赛

because they've got to stay in this ball game,

因为他们必须赢这场球赛。

they've got to win.

他们必须赢。

They come out lined up in the empty set,

他们出来在空设前排开，

three receivers to the right,

3个接球员在右边，

two to the left.

2个在左边。

Defense looks like they're gonna to man up with no safety.

防守看起来他们的位置不安全。

This is the exact offensive match-up that they want:

这正是他们需要防守的：

the best receiver lined up against the linebacker.

最好的接球员对着中后卫。

Quarterback steps back to receive the ball,

四分卫向后得到球，

five yards deep in the gun.

向端区有5码的距离。

He takes a snap, drops three steps,

他向后投球，后退3步，

he plants his back foot,

他后脚稳住，

he's looking for an opening.

他寻找空挡，

There's a blitz coming off the edge!

从边线又攻击！

He steps up to avoid the rush.

他向前冲避免攻击。

He's looking down field.

他向下看着操场。

He's got the inside receiver making a cut.

他让里面的接球员切入，

He's got a step on the linebacker.

他跑进中后卫位置。

Quarterback has a beat on it.

四分卫向他投球。

He lets the ball go,

他让球通过，

it's in the air!

球在空中飞！

Receiver is out in front of the defender.

接球员跑到防卫者前面。

He's got it beat!

他要拿到球！

He's out in front, racing for the ball!

他向前跑，冲向球！

It's coming down!

球落下来！

He cradles it at the fifteen!

他快速冲向15码！

He's at the ten, five!

他到10码 ，5 码！

Touchdown!

触地得分！

Unbelievable play!

无法相信的比赛！

Now, wait a minute.

现在，等一会儿。

Of course, it's believable,

当然，是可信的。

it's physics,

在物理学上，

specifically the differences between scalars and vectors.

特别是标量和矢量的不同。

So, let's just see that replay.

那么，让我们看下回放。

"Quarterback steps back to receive the ball,

“四分卫向后得到球，

five yards deep in the gun."

向端区前进5码。“

Stop.

停。

See, measurements are defined as two different quantities.

看下，测量被定义为两个不同的量。

Scalars are measurements with only numbers,

标量仅用一个数字度量，

and vectors are measurements with direction.

而矢量还需要方向。

For example, when that quarterback takes the snap,

例如：当四分卫向后投球时，

he's five yards away, but from where?

他有5码远，可是从哪开始呢？

Back from the line of scrimmage,

从争球线向后，

so the five yards by itself is a scalar quantity.

于是，只有5码是标量。

When you add a direction,

当你增加方向后，

like five yards deep,

像向里5码，

it becomes a vector quantity.

它就称为一个矢量。

Five yards - scalar,

5码-标量。

five yards deep - vector.

向里5码-矢量。

OK, go ahead.

好的，继续。

"He takes a snap, drops three steps.

“他向后投球，后退3步。

He plants his back foot, he's looking for an opening.

他稳住后脚，他寻找空挡。

There's a blitz coming off the edge!

从边上有进攻！

He steps up to avoid the rush."

他向前移动避开进攻。“

Whoa!

哇！

Here's a difference between distance and displacement.

距离和位移之间也有区别。

Distance is a measurement

距离是一个度量

without identifying where you moved.

没有考虑你从哪移动。

It's a scalar quantity.

它是一个标量。

When the quarterback makes a three-step drop,

当四分卫做出向后3步投球。

he moves about three yards back.

向后移动了3码。

When he moves about another three yards forward,

当他向前移动另外3码，

when he steps up into the pocket,

当他向前保护四分卫。

so that quarterback moves a total distance of six yards.

这样四分卫一共移动了6码的距离。

That's a distance, that's a scalar.

这是距离，是标量。

Now, displacement is a vector quantity,

现在，位移是矢量。

describing about how far out of place the object is.

表述物体离开他的位置多远。

So the quarterback dropped back three yards

这样，四分卫向后3码

and then moved back forward three yards,

然后向前移回3码。

he's in the exact same place where he started.

他又回到开始的位置。

So, his displacement is zero yards.

这样，他的位移是0码。

Distance - six yards,

距离-6码。

displacement - zero yards.

位移-0码。

So, let's look at what happened next.

好了，我们看看接下来发生什么。

"Quarterback has a beat on it, he let's the ball go!

“四分卫准备拿球，他让球过去！

It's in the air!

球在空中飞！

Receiver is out in front of the defender."

接球员走到防守者的前面。“

Stop.

停。

So, here's speed and velocity,

于是，这有速率和速度。

but let's just do one thing at a time.

可是我们一次只考虑一个事情。

So, speed is measurement without direction,

这样，速率是一种没有方向的度量，

it's a scalar quantity.

它是标量。

Velocity is a vector quantity.

速度是矢量。

It is that object's speed,

他是物体的速率，

but with a direction of motion.

而且是有方向的运动。

So the receiver accelerates away,

于是接球员加速离开，

gaining both speed and distance.

得到速率和距离。

This takes the receiver 5 seconds to run those 50 yards.

接球员5秒钟跑了50码。

So his average speed, in any given time,

这样他的平均速率，在任何给定时间，

is 10 yards/second.

是10码/秒。

The linebacker tries to keep up,

中后卫努力去阻止他，

but his overall speed is slower,

可是他的整个速率比他慢，

he only goes 35 yards in those 5 seconds,

他5秒钟仅仅跑了35码，

so his average speed is only 7 yards/second.

于是是他的平均速率仅是7码/秒。

They're both traveling in a forward direction,

他们都向相同的方向移动，

so their velocity is also positive.

于是他们的速度是正的。

You can't go from resting to your peak speed immediately.

你不能立刻从静止达到最高速率。

You've got to build up to it.

你需要逐渐增加速率。

This is acceleration.

这是加速度。

At first the linebacker can keep up with that receiver,

开始中后卫紧跟接球员，

but eventually the faster receiver pulls away.

可是最终较快的接球员跑开了。

That's acceleration, the change in speed over time.

这是加速度，速度随着时间变化。

Acceleration is a vector quantity.

加速度是矢量。

It describes a rate at which an object changes velocity.

它描述物体速度变化的比率。

Like velocity, acceleration is a vector.

像速度一样，加速度是矢量。

It happens in a direction.

它在一定的方向发生。

So let's just look at that play just one more time.

于是我们再看一次比赛回放。

"Quarterback steps back to receive the ball,

“四分卫向后让接球员拿到球，

five yards deep in the gun."

向端区前进5码。“

Vector!

矢量！

"He takes a snap, drops three steps,

“他向后投球，后退3步，

he plants his back foot.

他稳住后脚。

He's looking for an opening.

他寻找空挡。

There's a blitz coming off the edge!

从边上有进攻！

He steps up to avoid the rush."

他向前避开进攻。“

Displacement!

位移！

"He's got the inside receiver making a cut.

“他让里面的接球员切入。

He's got a step on the linebacker.

他在中后卫向前。

The quarterback has a beat on it.

四分卫投球。

He let's the ball go!

It's in the air!

他让球过去！

在空中飞！

Receiver is out in front of the defender!"

接球员跑到防卫者前面！“

Velocity!

速度！

"He's got it beat!

“他准备拿球！

He's out in front, racing for the ball!

他向前泡，冲向球！

It's coming down!

球落下！

He cradles it at the fifteen, he's at the ten, five!"

他到达15码线，他在10码， 5码！“

Acceleration!

加速度！

"Touchdown! Unbelievable play!

“触地得分！不可思议的比赛！

That was a great play as time expired,

当结束时那是一个伟大的比赛，

resulting in the touchdown

最终触地得分

and ultimately the win and pure effort."

最终获胜，真正的努力。“

And pure science.

真正的科学。