Prática de Shadowing: What is Voltage? - Aprenda a falar inglês com vídeo
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To understand how electricity works, we need to zoom in on atoms, the things that make up all matter.
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Atoms are made up of three basic particles.
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That is, protons, which have a positive electric charge, neutrons, which have no electric charge, and electrons, which have a negative electric charge.
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The protons and neutrons are tightly packed in the core or nucleus of an atom,
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while electrons move about this nucleus in regions known as shells or orbitals.
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Right now, this atom is electrically neutral, as it has the same number of protons and electrons.
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With enough energy, an electron may be stripped away, leaving the atom with a net positive charge.
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Likewise, another atom may receive a freed electron, which then makes the atom electrically negative.
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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.
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We can demonstrate this using a balloon and a soda can.
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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.
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As a result, this balloon now has a net negative charge.
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When we bring it close to the can, the can chases the balloon.
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Let's look at why that's happening.
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The aluminum in the can is a conductor, which means that the electrons can freely move about the material.
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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.
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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.
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Since the positive charges are closer to the balloon than the negative charges, the attractive force is greater than the repulsive force.
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This results in a net force that pulls the can toward the balloon.
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Let's see that again in instant replay.
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Before we go any further, let's talk about units.
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The SI unit for electric charge is the coulomb, generally abbreviated with an uppercase C.
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An electron has a charge of about negative 1 .602 times 10 to the negative 19th coulombs,
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and a proton has a charge of about positive 1 .602 times 10 to the negative 19th coulombs.
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Energy is usually given in joules, which is abbreviated with the symbol uppercase J.
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1 joule is equal to the amount of energy transferred to an object
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when a force of 1 newton is applied to that object over a distance of 1 meter.
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Energy can either be potential, which results from an object's position or arrangement, or kinetic, resulting from the object's motion.
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Both kinetic and potential energy are given in joules.
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Now we can define voltage.
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Voltage is a measure of electric potential between two points.
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The unit, volt, is defined as one joule of potential energy per unit charge given in coulombs.
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Let's explain this with an example.
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Let's say that I've got a particle with a negative one coulomb of charge.
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Then, let's say there is a particle with positive one coulomb of charge next to it.
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Since opposites attract and the positive particle is as close as it can get to the negative particle, everything is at rest.
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There is no kinetic or potential energy.
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Now, let's say
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that I need to use 10 joules of energy to move the positive particle from its resting position to this point.
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If I were to release it, it would move back to the negative particle.
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As a result, we can say that it has 10 joules of electric potential energy so long as I hold it here.
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Now, if I repeated this demo with three positively charged particles,
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it would take 30 joules of energy to move them the same distance away from the negative particle.
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So they have 30 joules of potential energy as long as I'm holding them here.
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As we defined earlier, voltage is the electric potential between two points.
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To calculate the voltage between their starting and ending points, we know that I did 30 joules of work to move the particles,
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and the total charge is 3 coulombs.
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So the voltage is 30 joules divided by 3 coulombs, which is 10 volts.
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We would say that the electric potential between these two points is 10 volts.
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If I released one of the particles, it would move back to the negatively charged particle.
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That would leave me with 20 joules of potential energy and 2 coulombs of charge, so the potential is still 10 volts.
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Even if I had no positive particles, the potential between the two points is still 10 volts.
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As you can see, electric potential energy is not the same as electric potential.
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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.
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Let's take a look at a battery.
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It doesn't really matter how far apart the terminals of a battery are.
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The chemicals inside a battery determine the electrical potential between the terminals.
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A fully charged AA alkaline battery is listed as having 1 .5 volts.
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That means each coulomb of charge moving from one end of the battery will do 1 .5 joules of work.
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Now, compare that to a much larger D -cell battery.
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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.
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As a result, D -cells will last a lot longer than AA batteries, doing the same amount of work.
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Static electricity can be a lot of fun, but more often than not, it's considered dangerous or a nuisance.
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One of the most dramatic displays of static electricity happens in nature.
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Storm clouds can build up a potential difference of millions of volts when compared to the Earth.
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And at some point, the electrons actually force their way through the air, creating lightning in order to balance out that charge difference.
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This sudden flow of electricity in an attempt to neutralize two statically charged objects is known as electrostatic discharge, or ESD.
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While lightning is a rather extreme display of electrostatic buildup and discharge, static electricity can still be quite useful.
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For example, many factory and power plant smokestacks employ a technology
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that uses static electricity to pull soot and ash out of the air as it flows up through the pipe, resulting in less pollution.
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Also, most cars are painted using a process called powder coating.
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In this, paint leaving the spray nozzle is given an electric charge, and the car body is given a different electric charge,
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which creates a stronger bond between the paint and the car body.
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This allows for a more uniform paint coverage
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and reduces paint waste since less of it's likely to stick around in the air or drip off the car body.
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Next time we'll dive into current electricity and talk about making it do work for us.
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Thank you.
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Vocabulário e dicas de fala para esta lição
Esta aula de conversação usa o vídeo “What is Voltage?”. As palavras que mais se repetem: charge, electron, energy, joule, balloon. Este vídeo tem 48 frases e 889 palavras para praticar shadowing. A fala dura 6:30. O falante mantém um ritmo estável de cerca de 137 palavras por minuto, confortável para o shadowing. Apenas 74% das palavras estão entre as 3.000 mais comuns do inglês, por isso o vocabulário é exigente.
Vocabulário principal deste vídeo
15 palavras do vídeo que vale a pena aprender, com pronúncia e significado:
| Palavra | Pronúncia | Significado |
|---|---|---|
| electricity substantivo | /ɪˌlɛkˈtɹɪsɪti/ | eletricidade |
| balloon substantivo | /bəˈlun/ | balão, bexiga |
| static adjetivo | /ˈstæt.ɪk/ | estático |
| voltage substantivo | /ˈvəʊltɪd͡ʒ/ | tensão, voltagem |
| particle substantivo | /ˈpɑɹtək(ə)l/ | partícula |
| atom substantivo | /ˈætəm/ | átomo |
| electron substantivo | /ɪˈlɛk.tɹɑn/ | elétron, eletrão |
| coat substantivo | /ˈkoʊ̯t/ | casaco, agasalho |
| strip verbo | /ˈstɹɪp/ | tirar, retirar |
| define verbo | /dɪˈfaɪn/ | definir |
| lightning substantivo | /ˈlaɪt.nɪŋ/ | relâmpago |
| excess substantivo | /ˈɛksɛs/ | excesso |
| attract verbo | /əˈtɹækt/ | atrair |
| depend verbo | /dɪˈpɛnd/ | depender |
| cloth substantivo | /klɒθ/ | pano, tecido |
Gramática neste vídeo
As estruturas que o falante mais usa, com as palavras exatas do vídeo:
| Estrutura | No vídeo |
|---|---|
| Voz passiva be + particípio passado — o foco está no que acontece, não em quem faz | are made · may be stripped · are pushed |
| Orações relativas who / which + oração — informação extra sobre uma pessoa ou coisa | protons, which have · conductor, which means · balloon, which is |
Pronúncia para ficar de olho
- Os sons de “th”: thirty /ˈθɝti/, cloth /klɒθ/
- Os sons de “sh” e “zh”: shell /ʃɛl/, ratio /ˈɹeɪ.ʃoʊ/, pollution /pəˈluʃən/, adhesion /ˌædˈhiː.ʒən/
- Palavras longas — acerte a sílaba tônica: electricity /ɪˌlɛkˈtɹɪsɪti/, aluminum /əˈlu.mɪ.nəm/, positively /ˈpɑ.zɪ.tɪv.li/, abbreviate /əˈbɹi.vi.eɪt/, electrically /ɪˈlɛk.tɹɪk.li/
Sons difíceis para falantes de português:
- Consoante final — sem acrescentar um “i” depois: static /ˈstæt.ɪk/, coat /ˈkoʊ̯t/, strip /ˈstɹɪp/, attract /əˈtɹækt/, depend /dɪˈpɛnd/
- /l/ final — a língua toca o céu da boca, não vira “u”: particle /ˈpɑɹtək(ə)l/, shell /ʃɛl/, terminal /ˈtɚmɪnəl/, neutral /ˈnuː.tɹəl/, joule /d͡ʒuːl/
- s + consoante no início — sem um “i” antes: static /ˈstæt.ɪk/, strip /ˈstɹɪp/, smokestack /ˈsmoʊkˌstæk/
Como praticar com este vídeo
- Ouça o vídeo inteiro uma vez sem falar e anote as palavras que você não conhece.
- Faça shadowing frase por frase na velocidade normal, repetindo cada uma até o seu ritmo ficar igual ao do falante.
- Grave a sua voz e compare com o original, prestando atenção a palavras como electricity, balloon, static.
O que é a Técnica de Shadowing?
Shadowing é uma técnica de aprendizado de idiomas com base científica, originalmente desenvolvida para o treinamento de intérpretes profissionais. O método é simples, mas poderoso: você ouve áudio em inglês nativo e repete imediatamente em voz alta — como uma sombra seguindo o falante com 1-2 segundos de atraso. Pesquisas mostram melhora significativa na precisão da pronúncia, entonação, ritmo, sons conectados, compreensão auditiva e fluência na fala.