How does work...work? - Peter Bohacek

Transcriber: Andrea McDonough Reviewer: Bedirhan Cinar

翻译人员: Yuyang Zhao 校对人员: Marini Qian

In Physics,

在物理学领域

the concepts of work and power help us understand

功和功率的概念帮助我们理解

and explain lots of things in our universe.

并解释宇宙中发生的很多事情

Let's start with work.

先从功开始说起

Positive work is the energy we put into a system,

正功指的是我们注入系统的能量

and negative work is energy that is transferred out.

负功则是它转化出的能量

Think of positive work as money being added to your bank account,

如果把正功比作是存入银行账户的钱的话

and negative work as money taken out.

那么负功就是从那儿取出的钱

In the metric system,

在度量单位里

work and energy are measured in Joules.

功和能都是通过焦耳来衡量的

As an example, let's take a beautiful, old, mechanical grandfather clock.

以一座精美的老式落地机械大摆钟为例

We transfer energy into the clock

当我们拉动曲柄

when we turn the crank

来举起摆钟内部的重重的金属缸体时

to raise the heavy metal cylinders inside the clock.

我们就是在把能量传递给了大摆钟

When we do this, we are doing positive work,

这就叫做做正功

adding energy to the clock,

为大摆钟注入能量的同时

and that energy is stored as gravitational potential energy.

这份能量被储存为重力势能

We can calculate the amount of work done by multiplying the force we apply

当我们计算做了多少功时

times the distance over which we apply the force.

可以将我们对物体施加的力乘以我们在施力方向上移动的距离

To raise the metal cylinders,

为了举起金属缸体

we need to apply a force equal to their weight.

我们需要施加一个和缸体等重的力

That is, equal to the force of gravity

即，和对汽缸向下作用的重力

pulling downward on the cylinders.

相等

These cylinders weight 300 Newtons,

这些汽缸重达300牛顿

which is pretty heavy,

这相当重

about as much as a small child,

相当于一个小孩的重量

and if we lift them 1/2 meter,

如果我们再把他们往上举1/2米

then we do 300 Newtons

那就算连续1/2米

times 1/2 meter

施300牛顿的力

or 150 Joules of work.

或是说做了150焦耳的功

Power is the rate at which energy is transferred.

功率是指能量转化的比率

When we say rate,

我们所说的比率

we mean the amount of energy transferred

是指每单位时间内

per unit of time.

被转化的能量的数量

In the metric system, power is measured in

在度量单位里，功率是通过

Joules per second,

每秒多少焦耳来衡量的

or Watts.

或是瓦特

The term Watt goes back to James Watt,

瓦特这个术语，要追溯到詹姆士·瓦特

who came up with the concept of horsepower

他提出了马力这个概念

to measure the amount of power

来衡量一匹典型的役马

produced by a typical work horse.

生产时的功率

James Watt was a producer of industrial steam engines,

詹姆士·瓦特制造了工业用的蒸汽机

and he wanted his potential customers

为了使他的潜在客户

to be able to make comparisons

能在他所制造的蒸汽机

between his steam engines and a familiar quanity,

和一个熟悉量

the power they could get from a working horse.

从一匹役马中获得的工作效率作比较

It was such a useful idea

用以詹姆士·瓦特来命名的瓦特

that the metric system unit for power, the Watt,

来作功率的单位

is named after James Watt.

真是个绝妙的想法

Following in James Watt's footsteps,

让我们来效仿詹姆士·瓦特

let's compare the amount of power it takes

来比较运行一座落地大摆钟所需消耗的功率

to run this grandfather clock

和一个100瓦特的电灯泡

to the power we'd need to run

所消耗的功率

a bright, 100-Watt light bulb.

We can measure the power a person uses

我们可以通过

to wind the clock

将一个人的工作量

by dividing the amount of work they did

除以他工作的时间

by the time it took them to do it.

来衡量他给钟上弦的功率

If it takes 1 minute, or 60 seconds,

如果他花了一分钟，或是说60秒

to lift the weights,

来举起这个重量的东西

then they are doing 150 Joules

那他们就做了150焦耳

divided by 60 seconds,

除以60秒的功率

or 2.5 Joules per second of work.

或是说每单位工作时间内2.5焦耳的功

They are adding energy to the clock

他们以2.5瓦特的功率

in the rate of 2.5 Watts.

给大摆钟增加能量

You would need about 40 times as much

以同样的功率，你需要40分钟

to run a bright, 100-Watt light bulb.

来点亮一枚100瓦特的电灯泡

Before we let the clock run,

在我们使大摆钟运行之前

the energy is stored

这份能量就已

as gravitational potential energy of the cylinders.

重力势能的形式，被储存在汽缸里了

It's like your bank account

这种情形，就像

when you have just deposited money.

你刚把钱存入银行账户

But if we let the clock run,

但如果我们要让大摆钟运行起来

the cylinders slowly move downward.

汽缸就要慢慢地向下移动

Energy is leaving the clock.

此时，能量会从大摆钟丧失

In fact, when the cylinders get to the bottom,

而事实上，当汽缸到达底部时

all the energy that we put in will have left.

我们注入的所有能量就已经释放完毕了

So how much power does the clock use?

那大摆钟究竟用了多少功率呢

That is, how many Joules of energy per second leave the clock

也就是说，如果汽缸需要五天的时间回到原来的位置

if it takes 5 days for the cylinders to return to their original position?

那么，每秒有多少焦耳的能量离开了大摆钟？

We can figure this out

我们能计算出来

because we already know how much work we did

因为我们已经知道

when we lifted the cylinders:

当我们举起汽缸时做了多少功：

150 Joules.

150焦耳

But this time, it took 5 days rather than a minute.

但这次，它需要花五天的时间而不是一分钟

Five days is 5 times 24

五天，就是5乘以24

times 60

乘以60

times 60 again

再乘以60

or 432,000 seconds.

或是说432,000秒

So we divide the work done by the time

因此，当我们讲所做的功除以做功的时间

and find the answer of about 0.00035 Joules per second,

就会得到每秒0.00035焦耳的结果

or about 0.35 milliwatts.

或是说0.35毫瓦

That's a tiny amount of power.

那是一个非常小的功率

This clock uses so little power

这个大摆钟消耗的功率如此小

that you could run almost 300,000 clocks

以至于点亮一枚100瓦特的电灯泡所需的同样功率

using the same power it takes to run one 100-Watt light bulb.

可以让300，000座大摆钟运转起来

That's right, you could run a clock in every house

的确如此，这个大小的功率

in a medium sized city with that much power.

足以在一个中等大小的城市里的任意家庭里运行起一座大摆钟

That's a pretty amazing conclusion

这是个相当令人惊奇的结论

and it took knowledge of work

并且它通过运用功

and power to figure it out.

和功率的知识来得出的