跟读练习: How do airplanes actually fly? - Raymond Adkins - 通过YouTube学习英语口语
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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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关于本课
这段视频将带您深入了解飞机飞行的奥秘，特别是“升力”是如何产生的。它不仅揭示了飞机飞行的科学原理，还纠正了一些常见的错误观念，甚至提到了爱因斯坦在航空设计上的尝试。通过本课，您将能：
- 学习航空物理和流体力学相关的英语词汇。
- 掌握如何清晰、有逻辑地解释复杂科学概念的语法模式。
- 练习在学术或专业场景下进行英语口语练习，如科普讲解、论文讨论。这对于提升您的英语流利度，尤其是准备雅思口语考试，非常有帮助。
重要词汇和短语
- fluid medium (流体介质): 指像空气或水这样可以流动的物质。
- stay aloft (保持飞行/在空中): 维持在空中飞行状态。
- thoroughly debunked (彻底驳斥/揭穿): 经过彻底证明是错误的理论或说法。
- centripetal acceleration (向心加速度): 物体沿曲线运动时指向圆心的加速度。
- pressure difference (压强差/压力差): 两个区域之间压力的差异，这是产生升力的关键。
- turbulent (紊流的/湍流的): 指流体流动不规则、不稳定的状态。
- confounding concept (令人困惑的概念): 难以理解或解释清楚的复杂概念。
- foray into aeronautics (涉足航空学领域): 初次尝试或进入航空学研究领域。
本视频练习技巧
这段视频语速适中，讲解清晰，非常适合进行跟读技巧训练和发音练习：
- 语速与清晰度： 视频讲解者语速平稳、发音清晰，有助于学习者模仿其在解释复杂概念时保持语速和清晰度。尝试逐句或逐段跟读，注意连接词和逻辑停顿。
- 口音与语调： 视频采用美式英语口音，发音标准。在跟读时，请特别留意专业词汇的重音和语调变化，例如“centripetal acceleration”、“pressure difference”。这对于提升您的英语发音练习质量至关重要。
- 话题难度与词汇： 视频内容涉及科学原理，词汇较为专业。建议在跟读前先理解内容，并查阅不熟悉的词汇发音。重点练习那些您觉得难以发音或不常使用的学术词汇。这能有效提高您在专业领域的英语口语练习能力。
什么是跟读法？
跟读法 (Shadowing) 是一种有科学依据的语言学习技巧，最初开发用于专业口译员的培训，并由多语言者Alexander Arguelles博士普及。这个方法简单而强大：您在听英语母语原声的同时立即大声重复——就像是一个延迟1-2秒紧跟说话者的影子。与被动听力或语法练习不同，跟读法强迫您的大脑和口腔肌肉同时处理并模仿真实的讲话模式。研究表明它能显着提高发音准确性，语调，节奏，连读，听力理解和口语流利度——使其成为雅思口语备考和真实英语交流最有效的方法之一。