Pratique du Shadowing: How do airplanes actually fly? - Raymond Adkins - Apprendre l'anglais à l'oral avec YouTube

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By 1917, Albert Einstein had explained the relationship between space and time.
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By 1917, Albert Einstein had explained the relationship between space and time.
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But, that year, he designed a flawed airplane wing.
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His attempt was based on an incomplete theory of flight.
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Indeed, insufficient and inaccurate explanations still circulate today.
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So, where did Einstein go wrong?
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And how do planes fly?
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Though we don’t always think of it this way, air is a fluid medium— it’s just less dense than liquids like water.
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Things that are lighter than air are buoyant within it, while heavier objects require an upward force, called lift, to stay aloft.
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For planes, this force is mostly generated by the wings.
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One especially pervasive false description of lift is the “Longer Path” or “Equal Transit Time” explanation.
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It states that air molecules traveling over the top of a curved wing cover a longer distance than those traveling underneath.
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For the air molecules above to reach the wing’s trailing edge in the same instance as those that split off and went below, air must travel faster above, creating a pocket of lower pressure that lifts the plane.
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This explanation has been thoroughly debunked.
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Air molecules floating above and below the wing don't need to meet back up.
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In reality, the air traveling above reaches the wing’s trailing edge much faster than the air beneath.
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To get a sense of how lift is actually generated, let's simulate an airplane wing in motion.
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As it moves forward, the wing affects the movement of the air around it.
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As air meets the wing’s solid surface, a thin layer sticks to the wing.
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This layer pulls the surrounding air with it.
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The air splits into pathways above and below the wing, following the wing’s contour.
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As the air that’s routed above makes its way around the nose of the wing, it experiences centripetal acceleration, the force you also feel in a sharply turning car.
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The air above therefore gathers more speed than the air traveling below.
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This increased speed is coupled with a decrease in pressure above the wing, which pulls even more air across the wing’s upper surface.
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The air flowing across the lower surface, meanwhile, experiences less of a change in direction and speed.
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The pressure across the wing’s lower surface is thus higher than that above the upper surface.
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This pressure difference results in the upwards force of lift.
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The faster the plane travels, the greater the pressure difference, and the greater that force.
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Once it overcomes the downward force of gravity, the plane takes off.
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Air flows smoothly around curved wings.
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But a wing’s curvature is not the cause of lift.
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In fact, a flat wing that’s tilted upwards can also create lift— as long as the air bends around it, contributing to and reinforcing the pressure difference.
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Meanwhile, having a wing that’s too curved or steeply angled can be disastrous:
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the airflow above may detach from the wing and become turbulent.
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This is probably what happened with Einstein’s wing design, nicknamed “the cat’s back.” By increasing the wing’s curvature, Einstein thought it would generate more lift.
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But one test pilot reported that the plane wobbled like “a pregnant duck” in flight.
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Our explanation is still a simplified description of this nuanced, complex process.
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Other factors, like the air that’s flowing meters beyond the wing’s surface— being swept up, then down— as well as air vortices formed at the wing’s tips, all influence lift.
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And, while experts agree that the pressure difference generates lift, their explanations for how can vary.
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Some might emphasize the air’s behavior at the wing’s surface, others the upward force created as the air is deflected downwards.
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However, there's no controversy when it comes to the math.
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Engineers use a set of formulas called the Navier-Stokes equations to precisely model air’s flow around a wing and detail how lift is generated.
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More than a century after Einstein’s foray into aeronautics, lift retains its reputation as a confounding concept.
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But when it feels like it’s all going to come crashing down, remember:
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it’s just the physics of fluid in motion.
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This video was made possible with support from Marriott Hotels.
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With over 590 hotels and resorts across the globe, Marriott Hotels celebrates the curiosity that propels us to travel.
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Check out some of the exciting ways TED-Ed and Marriott are working together, and book your next journey at Marriott Hotels.
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About This Lesson

Dive into the fascinating world of aeronautics with this insightful lesson that debunks common misconceptions about how airplanes fly. This video provides a clear, concise explanation of lift, revealing the true physics behind flight. For your English speaking practice, you'll encounter sophisticated vocabulary related to science, engineering, and fluid dynamics, offering an excellent opportunity to expand your academic lexicon. You'll practice understanding and explaining complex scientific principles, which is invaluable for improving your English fluency and communication skills in various contexts, including professional and academic discussions. Pay close attention to the speaker's clear articulation and logical flow, which serve as an excellent model for organizing your thoughts and presenting information effectively.

Key Vocabulary & Phrases

  • Fluid medium: A substance that flows and deforms under stress, like air or water. (e.g., "Air is a fluid medium—it’s just less dense than liquids like water.")
  • Stay aloft: To remain in the air or at a high altitude. (e.g., "Heavier objects require an upward force, called lift, to stay aloft.")
  • Thoroughly debunked: Proven to be false or incorrect after careful examination. (e.g., "This explanation has been thoroughly debunked.")
  • Centripetal acceleration: The acceleration directed towards the center of a circular path, causing an object to move in a curve. (e.g., "It experiences centripetal acceleration, the force you also feel in a sharply turning car.")
  • Turbulent airflow: Irregular or chaotic movement of air, often characterized by eddies and vortices. (e.g., "The airflow above may detach from the wing and become turbulent.")
  • Nuanced, complex process: A process that involves subtle distinctions and is intricate or difficult to understand. (e.g., "Our explanation is still a simplified description of this nuanced, complex process.")
  • Confounding concept: An idea or topic that is confusing or difficult to comprehend. (e.g., "Lift retains its reputation as a confounding concept.")

Practice Tips for This Video

To maximize your learning and pronunciation practice with this video, we recommend using the shadowing technique. The narrator speaks at a moderate and consistent pace, making it ideal for mimicking both the rhythm and intonation of standard American English. Focus on articulating the scientific terms clearly, such as "centripetal acceleration," "turbulent," and "Navier-Stokes equations." Pay attention to the linking sounds between words and how the speaker emphasizes key information. This video is particularly beneficial for those preparing for the IELTS speaking exam, as it provides excellent practice for describing processes and explaining complex ideas, especially in Part 3. Try to explain the concept of lift in your own words after shadowing, using the vocabulary you've learned. This will significantly boost your confidence and overall English fluency when discussing academic or technical subjects.

Qu'est-ce que la technique du Shadowing ?

Le Shadowing est une technique d'apprentissage des langues fondée sur la science, développée à l'origine pour la formation des interprètes professionnels. Le principe est simple mais puissant : vous écoutez de l'anglais natif et le répétez immédiatement à voix haute — comme une ombre suivant le locuteur avec un décalage de 1 à 2 secondes. Les recherches montrent une amélioration significative de la précision de la prononciation, de l'intonation, du rythme, des liaisons, de la compréhension orale et de la fluidité.

Comment pratiquer efficacement sur ShadowingEnglish

  1. Choisissez votre vidéo : Choisissez une vidéo YouTube avec un anglais clair et naturel. Les TED Talks, BBC News, scènes de films, podcasts sont parfaits. Collez l'URL dans la barre de recherche.
  2. Écoutez d'abord, comprenez le contexte : La première fois, gardez la vitesse à 1x et écoutez simplement. Ne répétez pas encore. Concentrez-vous sur la compréhension du sens.
  3. Configurez le mode Shadowing :
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  4. Faites du Shadowing à voix haute (la pratique essentielle) : Dès qu'une phrase est jouée — ou pendant la pause — répétez-la à voix haute, clairement et avec confiance. Imitez le rythme, les accents et l'intonation du locuteur.
  5. Augmentez le défi : Une fois à l'aise avec un passage, augmentez la vitesse à <code>1.25x</code> ou <code>1.5x</code>. Pratiquez 15 à 30 minutes par jour pour des résultats visibles en quelques semaines.

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