シャドーイング練習: What is Voltage? - 動画で英語スピーキングを学ぶ

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To understand how electricity works, we need to zoom in on atoms, the things that make up all matter.

Atoms are made up of three basic particles.

That is, protons, which have a positive electric charge, neutrons, which have no electric charge, and electrons, which have a negative electric charge.

The protons and neutrons are tightly packed in the core or nucleus of an atom,

while electrons move about this nucleus in regions known as shells or orbitals.

Right now, this atom is electrically neutral, as it has the same number of protons and electrons.

With enough energy, an electron may be stripped away, leaving the atom with a net positive charge.

Likewise, another atom may receive a freed electron, which then makes the atom electrically negative.

When we have two objects with different electric charges due to the absence or presence of excess electrons, we say that we have static electricity.

We can demonstrate this using a balloon and a soda can.

When I rub a piece of cloth against the balloon, I strip away electrons from the piece of cloth and add them to the balloon.

As a result, this balloon now has a net negative charge.

When we bring it close to the can, the can chases the balloon.

Let's look at why that's happening.

The aluminum in the can is a conductor, which means that the electrons can freely move about the material.

As we bring the negatively charged balloon near the metal, the electrons are pushed away to the far side of the can since like charges repel.

That leaves an excess of positive charge on the side of the can nearest the balloon, which is pulled toward the balloon as opposite charges attract.

Since the positive charges are closer to the balloon than the negative charges, the attractive force is greater than the repulsive force.

This results in a net force that pulls the can toward the balloon.

Let's see that again in instant replay.

Before we go any further, let's talk about units.

The SI unit for electric charge is the coulomb, generally abbreviated with an uppercase C.

An electron has a charge of about negative 1 .602 times 10 to the negative 19th coulombs,

and a proton has a charge of about positive 1 .602 times 10 to the negative 19th coulombs.

Energy is usually given in joules, which is abbreviated with the symbol uppercase J.

1 joule is equal to the amount of energy transferred to an object

when a force of 1 newton is applied to that object over a distance of 1 meter.

Energy can either be potential, which results from an object's position or arrangement, or kinetic, resulting from the object's motion.

Both kinetic and potential energy are given in joules.

Now we can define voltage.

Voltage is a measure of electric potential between two points.

The unit, volt, is defined as one joule of potential energy per unit charge given in coulombs.

Let's explain this with an example.

Let's say that I've got a particle with a negative one coulomb of charge.

Then, let's say there is a particle with positive one coulomb of charge next to it.

Since opposites attract and the positive particle is as close as it can get to the negative particle, everything is at rest.

There is no kinetic or potential energy.

Now, let's say

that I need to use 10 joules of energy to move the positive particle from its resting position to this point.

If I were to release it, it would move back to the negative particle.

As a result, we can say that it has 10 joules of electric potential energy so long as I hold it here.

Now, if I repeated this demo with three positively charged particles,

it would take 30 joules of energy to move them the same distance away from the negative particle.

So they have 30 joules of potential energy as long as I'm holding them here.

As we defined earlier, voltage is the electric potential between two points.

To calculate the voltage between their starting and ending points, we know that I did 30 joules of work to move the particles,

and the total charge is 3 coulombs.

So the voltage is 30 joules divided by 3 coulombs, which is 10 volts.

We would say that the electric potential between these two points is 10 volts.

If I released one of the particles, it would move back to the negatively charged particle.

That would leave me with 20 joules of potential energy and 2 coulombs of charge, so the potential is still 10 volts.

Even if I had no positive particles, the potential between the two points is still 10 volts.

As you can see, electric potential energy is not the same as electric potential.

When we start talking about moving electrons through conductors and electronic components, we are talking about current electricity, which is slightly different than static electricity.

Let's take a look at a battery.

It doesn't really matter how far apart the terminals of a battery are.

The chemicals inside a battery determine the electrical potential between the terminals.

A fully charged AA alkaline battery is listed as having 1 .5 volts.

That means each coulomb of charge moving from one end of the battery will do 1 .5 joules of work.

Now, compare that to a much larger D -cell battery.

Each coulomb of charge will still only do 1 .5 joules of work, but a D -cell has far more coulombs of charge than a AA.

As a result, D -cells will last a lot longer than AA batteries, doing the same amount of work.

Static electricity can be a lot of fun, but more often than not, it's considered dangerous or a nuisance.

One of the most dramatic displays of static electricity happens in nature.

Storm clouds can build up a potential difference of millions of volts when compared to the Earth.

And at some point, the electrons actually force their way through the air, creating lightning in order to balance out that charge difference.

This sudden flow of electricity in an attempt to neutralize two statically charged objects is known as electrostatic discharge, or ESD.

While lightning is a rather extreme display of electrostatic buildup and discharge, static electricity can still be quite useful.

For example, many factory and power plant smokestacks employ a technology

that uses static electricity to pull soot and ash out of the air as it flows up through the pipe, resulting in less pollution.

Also, most cars are painted using a process called powder coating.

In this, paint leaving the spray nozzle is given an electric charge, and the car body is given a different electric charge,

which creates a stronger bond between the paint and the car body.

This allows for a more uniform paint coverage

and reduces paint waste since less of it's likely to stick around in the air or drip off the car body.

Next time we'll dive into current electricity and talk about making it do work for us.

Thank you.

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このレッスンの語彙とスピーキングのポイント

このスピーキングレッスンは、動画「What is Voltage?」を教材にしています。繰り返し出てくる語は次のとおりです：charge, electron, energy, joule, balloon。この動画には、シャドーイング用の文が48文、単語が889語あります。音声の長さは6:30です。話す速さは1分あたり約137語で安定しており、シャドーイングしやすいペースです。英語の頻出3,000語に含まれる単語は74%だけなので、語彙は難しめです。

この動画の重要語彙

動画に出てくる覚えておきたい単語15語を、発音と意味つきで紹介します。

単語	発音	意味
balloon 名詞	/bəˈlun/	バルーン, 気球
static 形容詞	/ˈstæt.ɪk/	静的
voltage 名詞	/ˈvəʊltɪd͡ʒ/	電圧
particle 名詞	/ˈpɑɹtək(ə)l/	粒子
atom 名詞	/ˈætəm/	原子, アトム
electron 名詞	/ɪˈlɛk.tɹɑn/	電子
coat 名詞	/ˈkoʊ̯t/	コート, 外套
strip 動詞	/ˈstɹɪp/	剥ぐ, 外す
lightning 名詞	/ˈlaɪt.nɪŋ/	稲妻, 雷光
attract 動詞	/əˈtɹækt/	引きつける
depend 動詞	/dɪˈpɛnd/	依存する
cloth 名詞	/klɒθ/	布
minus	/ˈmaɪ.nəs/	引く
conductor 名詞	/kənˈdʌktɚ/	指揮者
nucleus 名詞	/ˈnuː.kli.əs/	核, 核心

この動画の文法

話し手がよく使っている文型を、動画の実際の表現とともに紹介します。

文型	動画での表現
受動態 be + 過去分詞 — 誰がするかより、何が起きるかに焦点を当てる	are made · may be stripped · are pushed
関係詞節 who / which + 節 — 人や物について情報を加える	protons, which have · conductor, which means · balloon, which is

注意したい発音

「th」の音: thirty /ˈθɝti/, cloth /klɒθ/
「sh」と「zh」の音: shell /ʃɛl/, ratio /ˈɹeɪ.ʃoʊ/, pollution /pəˈluʃən/, adhesion /ˌædˈhiː.ʒən/
長い単語（アクセントの位置に注意）: electricity /ɪˌlɛkˈtɹɪsɪti/, aluminum /əˈlu.mɪ.nəm/, positively /ˈpɑ.zɪ.tɪv.li/, abbreviate /əˈbɹi.vi.eɪt/, electrically /ɪˈlɛk.tɹɪk.li/

日本語話者が苦手な音：

/r/ と /l/ の区別 — /l/ は舌先を歯茎につけ、/r/ はどこにもつけない: electricity /ɪˌlɛkˈtɹɪsɪti/, particle /ˈpɑɹtək(ə)l/, electron /ɪˈlɛk.tɹɑn/, relative /ˈɹɛl.ə.tɪv/, explore /ɪkˈsploɹ/
/v/ — /b/ にならないように、上の歯を下唇に当てる: voltage /ˈvəʊltɪd͡ʒ/, relative /ˈɹɛl.ə.tɪv/, divide /dɪˈvaɪd/, positively /ˈpɑ.zɪ.tɪv.li/, volt /vəʊlt/
/f/ — 「フ」ではなく、上の歯と下唇で出す: define /dɪˈfaɪn/, uniform /ˈjunɪˌfɔɹm/, leaf /lif/, freely /ˈfɹili/

この動画での練習方法

まず声を出さずに動画を最後まで聞き、知らない単語をメモします。
通常の速度で一文ずつシャドーイングし、話し手のリズムに合うまで繰り返します。
自分の声を録音して元の音声と比べます。balloon, static, voltageなどの単語に特に注意しましょう。

シャドーイングとは？英語上達に効果的な理由

シャドーイング（Shadowing）は、もともとプロの通訳者養成プログラムで開発された言語学習法で、多言語習得者として知られるDr. Alexander Arguelles によって広く普及されました。方法はシンプルですが非常に効果的：ネイティブスピーカーの英語を聞きながら、1〜2秒の遅延で声に出してすぐに繰り返す——まるで「影（shadow）」のように話者を追いかけます。文法ドリルや受動的なリスニングと異なり、シャドーイングは脳と口の筋肉が同時にリアルタイムで英語を処理・再現することを強制します。研究により、発音精度、抑揚、リズム、連音、リスニング力、そして会話の流暢さが大幅に向上することが確認されています。IELTSスピーキング対策や自然な英語コミュニケーションを目指す方に特におすすめです。

シャドーイングのやり方: ステップ別の完全ガイドを読む →

シャドーイング練習: What is Voltage? - 動画で英語スピーキングを学ぶ

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