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  • In Physics,

    在物理學中

  • the concepts of work and power help us understand

    「功」 (work) 與「功率」 (power) 幫我們了解

  • and explain lots of things in our universe.

    並解釋宇宙的許多現象

  • Let's start with work.

    我們先從功談起

  • Positive work is the energy we put into a system,

    正向的功是指投入系統的能量

  • and negative work is energy that is transferred out.

    負向的功是指系統放出的能量

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

    正功相當於在銀行存錢

  • and negative work as money taken out.

    負功相當於把錢領出來

  • In the metric system,

    在公制系統

  • work and energy are measured in Joules.

    功和能量的單位是焦耳 (Joule)

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

    以優美的機械式老爺鐘為例

  • We transfer energy into the clock

    我們把能量傳進時鐘裡

  • when we turn the crank

    是靠旋轉曲柄

  • to raise the heavy metal cylinders inside the clock.

    抬高裡面的金屬重錘

  • When we do this, we are doing positive work,

    如此我們做了正功

  • adding energy to the clock,

    把能量加到時鐘裡

  • and that energy is stored as gravitational potential energy.

    能量以重力位能的形式儲存

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

    要計算做的功,可將所施的力

  • times the distance we over which we apply the force.

    乘以施力的距離

  • To raise the metal cylinders,

    要把金屬重錘抬高

  • we need to apply a force equal to their weight.

    所施的力,等於其重量

  • That is, equal to the force of gravity

    也就是重力

  • pulling downward on the cylinders.

    往下拉金屬重錘的力

  • These cylinders weight 300 Newtons,

    金屬重錘的重量為 300 牛頓

  • which is pretty heavy,

    蠻重的

  • about as much as a small child,

    相當於一個小孩的重量

  • and if we lift them 1/2 meter,

    如果我們抬高 1/2 公尺

  • then we do 300 Newtons

    我們就做了 300 牛頓

  • times 1/2 meter

    乘以 1/2 公尺

  • or 150 Joules of work.

    等於 150 焦耳的功

  • Power is the rate at which energy is transferred.

    功率 (power) 是指能量傳遞的速率

  • When we say rate,

    當我們說速率的時候

  • we mean the amount of energy transferred

    我們指的是

  • per unit of time.

    單位時間內,傳送的能量

  • In the metric system, power is measured in

    功率的公制單位為

  • Joules per second,

    每秒的焦耳數

  • or Watts.

    也就是「瓦特」 (Watt)

  • The term Watt goes back to James Watt,

    這個名詞來自詹姆斯瓦特 (James Watt)

  • who came up with the concept of horsepower

    他提出了「馬力」的想法

  • to measure the amount of power

    要度量功率

  • produced by a typical work horse.

    可採用一般工作馬匹為基準

  • James Watt was a producer of industrial steam engines,

    瓦特是工業用蒸汽機的製造商

  • and he wanted his potential customers

    他希望潛在客戶

  • to be able to make comparisons

    能夠比較

  • between his steam engines and a familiar quanity,

    他的蒸汽機,及大家熟悉的度量…

  • the power they could get from a working horse.

    也就是工作馬匹的力量

  • It was such a useful idea

    這是個有用的想法

  • that the metric system unit for power, the Watt,

    所以公制的功率單位-瓦特

  • is named after James Watt.

    就是以他為名

  • Following in James Watt's footsteps,

    追隨瓦特的腳步

  • let's compare the amount of power it takes

    我們來比較一下

  • to run this grandfather clock

    讓老爺鐘運作

  • to the power we'd need to run

    的功率以及

  • a bright, 100-Watt light bulb.

    讓 100 瓦燈泡發亮的功率

  • We can measure the power a person uses

    要算出

  • to wind the clock

    幫老爺鐘上發條的功率

  • by dividing the amount of work they did

    只要把所做的功

  • by the time it took them to do it.

    除以所花的時間

  • If it takes 1 minute, or 60 seconds,

    如果花了 1 分鐘,也就是 60 秒

  • to lift the weights,

    抬起重錘

  • then they are doing 150 Joules

    把 150 焦耳的功

  • divided by 60 seconds,

    除以 60 秒時間

  • or 2.5 Joules per second of work.

    就得到功率,每秒 2.5 焦耳

  • They are adding energy to the clock

    將能量加進時鐘的功率

  • in the rate of 2.5 Watts.

    是 2.5 瓦特

  • You would need about 40 times as much

    要 40 倍這樣的能量

  • to run a bright, 100-Watt light bulb.

    才能讓 100 瓦的燈泡發亮

  • Before we let the clock run,

    在我們讓時鐘運轉前

  • the energy is stored

    能量以

  • as gravitational potential energy of the cylinders.

    重力位能的形式儲存在圓柱中

  • It's like your bank account

    相當於把錢

  • when you have just deposited money.

    存入銀行

  • But if we let the clock run,

    如果我們讓時鐘開始運轉

  • the cylinders slowly move downward.

    圓柱就會緩緩下降

  • Energy is leaving the clock.

    能量開始從時鐘流失

  • In fact, when the cylinders get to the bottom,

    當圓柱到達底部的時候

  • all the energy that we put in will have left.

    所有存進去的能量都用完了

  • So how much power does the clock use?

    時鐘所用的功率是多少?

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

    就是每秒有多少焦耳流出時鐘?

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

    假設 5 天後圓柱完全降下

  • We can figure this out

    我們可以算出功率

  • because we already know how much work we did

    我們已知抬升圓柱時

  • when we lifted the cylinders:

    所做的功

  • 150 Joules.

    是 150 焦耳

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

    時間是 5 天,而不是 1 分鐘

  • Five days is 5 times 24

    5 天相當於 5 乘以 24 小時

  • times 60

    乘以 60 分鐘

  • times 60 again

    再乘以 60 秒

  • or 432,000 seconds.

    也就是 432,000 秒

  • So we divide the work done by the time

    我們把所做的功除以時間

  • and find the answer of about 0.00035 Joules per second,

    得到每秒 0.00035 焦耳

  • or about 0.35 milliwatts.

    也就是 0.35 毫瓦

  • That's a tiny amount of power.

    這是很小的功率

  • This clock uses so little power

    時鐘用的功率極小

  • that you could run almost 300,000 clocks

    表示 30 萬個時鐘運作的功率

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

    等於一個 100 瓦燈泡的功率

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

    沒錯,這足夠在一個中型城市裡

  • in a medium sized city with that much power.

    讓家家戶戶的時鐘運作了

  • That's a pretty amazing conclusion

    這是很神奇的結論

  • and it took knowledge of work

    只要你有功和功率的知識

  • and power to figure it out.

    就可以算得出來

In Physics,

在物理學中

字幕與單字

單字即點即查 點擊單字可以查詢單字解釋

B1 中級 中文 TED-Ed 功率 時鐘 焦耳 能量 圓柱

TED-Ed】工作......是如何進行的?- Peter Bohacek (【TED-Ed】How does work...work? - Peter Bohacek)

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    稲葉白兎 發佈於 2021 年 01 月 14 日
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