Prática de Shadowing: TOEFL Listening Practice #3 | Academic Lecture + Questions & Answers - Aprenda a falar inglês com vídeo
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You are about to listen to a TOEFL-style academic lecture.
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Listen carefully and take notes.
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You'll answer questions at the end.
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Let's begin.
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Alright, so last time we talked about some of the basic properties of stars.
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Temperature, brightness, distance.
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And today I want to start with a question that seems almost impossible to answer.
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What are stars made of?
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Now, think about the problem for a second.
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If a geologist wants to know what a rock is made of, what can she do?
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Take a sample?
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Exactly.
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Bring it into a laboratory, analyze it chemically.
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But obviously we can't do that with a star.
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Even the Sun is about 150 million kilometers away, and other stars are much, much farther.
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So how can astronomers say that a particular star contains hydrogen, helium, sodium, calcium, whatever?
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How can we know what's there without ever collecting a sample?
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The answer is light, more specifically something called spectroscopy.
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Now, you've probably seen what happens when white light passes through a prism.
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It makes a rainbow.
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Right.
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The light separates into different colors or different wavelengths.
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And if you do this carefully with light from a star, you get what we call a spectrum.
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But a stellar spectrum isn't usually just a smooth rainbow.
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There are dark lines at particular places in it.
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These are called absorption lines.
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And those little dark lines are enormously useful.
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In fact, you can think of them as… Well, almost like fingerprints. of the star?
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Not exactly of the star itself.
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Fingerprints of the chemical elements in the star's atmosphere.
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Let me explain.
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Every chemical element interacts with light in its own characteristic way.
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Hydrogen absorbs light at certain specific wavelengths.
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Sodium absorbs at another set of wavelengths.
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Calcium has its own pattern.
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So if astronomers see the characteristic absorption pattern of hydrogen in a star's spectrum, they know hydrogen is present.
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If they see the pattern associated with sodium, they know sodium is present.
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And so on.
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But how do they know which lines belong to which element in the first place?
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Good, that's the important part.
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We can determine that here on Earth.
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In a laboratory, scientists can heat different elements and examine the wavelengths of light associated with them.
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Each element produces a distinctive pattern.
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Then astronomers compare those laboratory patterns with the lines they observe in starlight.
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If the patterns match, they can identify the element, so we're not guessing what stars contain.
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We're comparing astronomical observations with measurements that can be reproduced in a laboratory.
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Now this idea became extremely important in the 19th century.
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And there's a nice historical example involving the Sun.
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Astronomers studying sunlight noticed a set of spectral lines that didn't match any element known at the time.
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So they proposed that there must be an element in the Sun that hadn't yet been discovered on Earth.
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Wait!
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They discovered an element in the Sun before they found it here?
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Exactly.
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That element was helium.
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The name actually comes from Helios, the Greek word associated with the Sun.
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Helium was identified in the solar spectrum before scientists confirmed its presence on Earth.
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And think about why that's significant.
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It demonstrated that spectroscopy could tell us about matter in a place we couldn't physically visit.
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That's a pretty remarkable idea.
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Now, I want to be careful here because there's an easy misunderstanding.
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When we look at a star's spectrum, we aren't necessarily seeing the composition of the entire star equally.
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Most of the absorption lines we observe are produced by material in the star's outer layers, its atmosphere.
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So we don't actually know what's inside the star?
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Well, that's going a little too far.
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We can learn about stellar interiors using other evidence and physical models.
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But spectroscopy gives us the most direct information about the material interacting with the light we observe, especially in the outer layers.
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So when you hear someone say, we know what the star is made of because of its spectrum, remember that there's a little more complexity behind that statement.
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Now, chemical composition isn't the only thing a spectrum can tell us.
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This is where it gets even more useful.
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Suppose I know exactly where a particular hydrogen line should appear.
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I look at a star, and the same line is there, but it's shifted slightly toward the red end of the spectrum.
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What might cause that?
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The star is cooler?
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can affect a spectrum, yes, but that's not what I'm describing here.
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If the whole pattern shifts toward longer, redder wavelengths, that can indicate that the star is moving away from us.
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And if the lines shift toward shorter, bluer wavelengths, it's moving toward us?
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Right?
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This is related to the Doppler effect.
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You've experienced the same basic phenomenon Imagine an ambulance approaching you with its siren on.
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The pitch sounds higher as it approaches and lower after it passes and moves away.
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With light, instead of hearing a change in pitch, we observe a change in wavelength.
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Movement away produces what we call a red shift.
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Movement toward us produces a blue shift.
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Now, don't take the ambulance analogy too literally.
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Sound waves and light waves aren't identical, and they don't travel in the same way.
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The analogy is useful because in both cases, relative motion affects the waves we observe.
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So from one spectrum you can tell what a star contains and whether it's moving?
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Yes, and potentially more than that.
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Spectra can provide information about temperature, density, rotation, magnetic fields.
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But for today I want you to remember the two basic ideas we've discussed.
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First, pattern of spectral lines can identify chemical elements.
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Second, shift.
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In the position of those lines can give us information about motion.
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Pattern tells us something about composition, shift tells us something about movement.
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Those are different pieces of information coming from the same starlight, and that's really the larger point.
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Astronomy often works this way.
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We can't touch most of the things we study, we can't bring a star into a laboratory, but the light reaching us carries information.
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The challenge is learning how to read it.
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Questions.
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1. What is the lecture mainly about?
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2. Why does the professor compare spectral lines to fingerprints?
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3. Why does the professor discuss the discovery of helium?
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4. Why does the professor say, well, that's going a little too far?
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5. According to the professor, what are two types of information that astronomers can obtain from spectral lines?
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6. What is the purpose of the professor's example of an ambulance siren?
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1. Correct answer.
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B. How astronomers use starlight to learn about stars.
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The lecture focuses on spectroscopy and the information astronomers can obtain by analyzing light from stars.
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The professor explains how spectral lines reveal chemical composition
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and how shifts in those lines can indicate whether a star is moving toward or away from Earth.
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Why the other answers are incorrect.
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A is incorrect because differences in stellar brightness are not the main subject.
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C is incorrect because laboratory experiments actually play an important role in identifying spectral patterns.
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D is incorrect because the lecture does not explain how astronomers calculate stellar distances.
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2. Correct answer.
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A. To emphasize that each chemical element has a distinctive spectral pattern.
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The professor explains that hydrogen, sodium, calcium, and other elements interact with light at specific wavelengths.
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Because each element has a characteristic pattern, Astronomers can compare the lines in starlight with patterns measured in laboratories.
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The fingerprint analogy emphasizes distinctive identification.
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The professor also immediately qualifies the analogy, the lines are not fingerprints of an individual star but of the chemical elements present in its atmosphere.
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3. Correct answer.
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C. To provide an example of spectroscopy revealing matter that had not yet been identified on Earth.
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Astronomers observed spectral lines in sunlight that did not match any element known at the time.
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They concluded that an unknown element must be present in the sun.
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That element was later identified as helium.
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The example demonstrates the power of spectroscopy.
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Scientists could identify evidence of a chemical element in a place they could not physically visit.
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4. Correct answer.
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A. The student has incorrectly concluded that astronomers know nothing about stellar interiors.
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The professor explains that absorption lines mainly provide direct information about material in a star's outer layers.
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The student then asks whether this means scientists do not know what is inside stars.
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The professor's response, that's going a little too far, signals that the student's conclusion is too strong.
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Astronomers can still learn about stellar interiors using other observations and physical models.
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This is a typical TOEFL speaker purpose flash function question.
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The professor is qualifying a student's interpretation rather than rejecting the original concept.
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5. Correct answers.
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A and C.
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The chemical composition of a star and the direction of a star's motion relative to Earth.
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The pattern of absorption lines can identify chemical elements.
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A shift in those lines can reveal relative motion.
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A red shift can indicate movement away from Earth, while a blue shift can indicate movement toward Earth.
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The professor summarizes this distinction near the end of the lecture.
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Pattern is composition.
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Shift is movement.
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6. Correct answer.
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C. To illustrate how relative motion can affect observed waves.
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The professor uses the familiar example of an ambulance siren to introduce the Doppler effect.
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As an ambulance approaches, its perceived pitch is higher.
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As it moves away, the pitch becomes lower.
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A related effect occurs with light.
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Instead of a change in perceived pitch, astronomers observe a change in wavelength.
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The professor also warns students not to take the analogy too literally because sound and light are different kinds of waves.
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The purpose of the example is therefore to make the general relationship between relative motion and observed waves easier to understand.
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Vocabulário e dicas de fala para esta lição
Este vídeo tem 153 frases e 1628 palavras para praticar shadowing. A fala dura 11:32. O falante mantém um ritmo estável de cerca de 141 palavras por minuto, confortável para o shadowing. Apenas 76% 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 |
|---|---|---|
| element substantivo | /ˈɛləmənt/ | fundamento |
| spectrum substantivo | /ˈspɛktɹəm/ | espectro, espetro |
| observe verbo | /əbˈzɜːv/ | seguir, acompanhar |
| laboratory substantivo | /ˈlæb(ə)ɹəˌtɔɹi/ | laboratório |
| composition substantivo | /ˌkɑm.pəˈzɪʃ.ən/ | composição |
| hydrogen substantivo | /ˈhaɪdɹəd͡ʒ(ə)n/ | hidrogênio, hidrogénio |
| stellar adjetivo | /ˈstɛl.əɹ/ | estelar |
| relative substantivo | /ˈɹɛl.ə.tɪv/ | parente, parenta |
| pitch substantivo | /pɪt͡ʃ/ | arremesso |
| lecture substantivo | /ˈlɛk.t͡ʃə/ | conferência, palestra |
| ambulance substantivo | /ˈæmbjᵿl(ə)n(t)s/ | ambulância |
| sodium substantivo | /ˈsəʊ.di.əm/ | sódio |
| analogy substantivo | /əˈnæləd͡ʒi/ | analogia |
| absorption substantivo | /æbˈsɔɹp.ʃn̩/ | absorção |
| compare verbo | /kəmˈpɛɚ/ | comparar |
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 | is made · are called · can be reproduced |
| Present perfect have/has + particípio passado — uma ação passada que ainda importa agora | you've probably seen · You've experienced · we've discussed |
Pronúncia para ficar de olho
O falante usa 20 contrações e formas reduzidas, como can't, don't, aren't. Diga-as na forma curta, do jeito que você ouve.
- Os sons de “th”: smooth /smuːð/, wavelength /ˈweɪvˌlɛŋ(k)θ/
- Os sons de “sh” e “zh”: composition /ˌkɑm.pəˈzɪʃ.ən/, absorption /æbˈsɔɹp.ʃn̩/, associate /əˈsoʊʃi.ət/, observation /ˌɑbzɚˈveɪʃn̩/, flash /flæʃ/
- Palavras longas — acerte a sílaba tônica: laboratory /ˈlæb(ə)ɹəˌtɔɹi/, composition /ˌkɑm.pəˈzɪʃ.ən/, analogy /əˈnæləd͡ʒi/, associate /əˈsoʊʃi.ət/, characteristic /ˌkæɹ(ə)ktəˈɹɪstɪk/
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 element, spectrum, observe.
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.