シャドーイング練習: Material Properties 101 - 動画で英語スピーキングを学ぶ
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This video is going to be a bit different to my usual videos, but I want to talk about material properties and the words we use to describe them.
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This is information you are going to need to fully understand future videos.
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By the end of this video, I want you to understand 6 keywords that we use to describe materials.
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These are stiff, strong, ductile, brittle, tough and hard.
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With these words, you will be able to describe pretty much any material
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and better understand why certain materials are used in different applications.
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More technical videos like this will be uploaded to my second channel from now on, which you can subscribe to by following this link.
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I'll try and back up the technical stuff with interesting real-world examples.
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First we are going to learn what a tensile test is.
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A tensile test is a fundamental test in material mechanics.
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It's performed by pulling a sample of material apart until failure, while measuring the force and displacement.
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It provides us with something called a stress strain curve, which tells us a lot about the material's reactions to forces.
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In this scenario, the stress is defined by the force applied to the test sample, divided by the cross-sectional area.
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This gives us units of newtons per meter squared, which you may recognize as the metric unit for pressure, Pascals.
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Stress goes on the y-axis.
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Strain describes how much deformation has occurred with that applied force, and it is found by dividing the change in length by the original length.
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This is placed on the x-axis.
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Let's watch this test again and see what information we can get from the stress strain graph.
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As the stress rises, the material begins to deform.
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This initial linear region is elastic deformation, That means if we remove the force, the material will regain its original shape.
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Think of how a rubber band can deform hugely and still come back to its original shape.
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The end of this linear elastic deformation is marked by the yield point.
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From here out, any additional stress will cause permanent deformation.
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This is called plastic deformation.
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The stress continues to rise until it hits the ultimate tensile strength point.
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This is the ultimate strength of the material, the most stress it can handle.
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From here, less stress is needed as the material begins to decrease in cross section, which you can see happening here.
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This is called necking.
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This continues until the material fractures.
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We can get a lot of really useful information from this graph.
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The first is Young's modulus, otherwise known as the elastic modulus.
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This describes how stiff the material is, and it is obtained by finding the slope of this linear region.
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A steeper slope means a stiffer material.
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For example, a high carbon steel may look like this, whereas a flexible material with the low Young's modulus, like rubber, would look like this.
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This graph is not to scale, but it should give you an idea of how this information is represented.
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Young's modulus is one of the most used properties in engineering, as we can use it to predict deflection in a huge range of scenarios.
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Yield strength and ultimate tensile strength are two other important properties.
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An engineer will divide the yield or ultimate strength by the safety factor to achieve the max allowable stress, which is used to influence the design of the product.
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Usually engineers will aim to keep the max possible stress well below failure, but safety factors differ between industries.
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So we've seen a stiff material and a flexible material.
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Now let's look at a material in between.
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This material can be described as tuff and ductile.
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Tuff simply means the material can absorb a lot of energy without breaking.
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The area under the graph here defines how much energy is absorbed.
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Ductile means it deforms under pressure.
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The two previous materials could also be considered ductile.
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Springsteel is a tough and ductile material with a high yield strength which is why it is used in springs.
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Springs need to absorb energy without permanently deforming.
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The opposite of ductile is brittle.
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A brittle material is a material that breaks with very little deformation.
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Glass, ceramics and cast iron all fall into this category.
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You can actually tell if a material is brittle or ductile by examining the fracture surface after they have broken.
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A ductile material will have this characteristic cup and cone fracture surface, whereas brittle fractures have granular flat looking fracture surfaces.
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Some materials can go from ductile to brittle when their temperatures are lowered.
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This was actually a massive problem during World War 2 with the Liberty ship.
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Several Several of these ships literally broke in half with no warning, including the SS John P.
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Gaines, which broke in half in the frigid waters of the Bering Sea.
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It was later discovered that the grade of steel being used became brittle at lower temperatures.
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This problem was made worse by the stress concentration at the hatches, which you learned about in my first video, Why are plane windows round?
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This embrittlement is also thought to have contributed to the fracture of the titanic's hull.
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The final material property I want to talk about is hardness.
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It is directly related to the stiffness and yield strength of the material, but it is used to describe how difficult it is to dent, scratch and abrade materials.
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One way this material property is measured is with the Rockwell hardness test.
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This test involves three steps.
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First a minor load is applied to the material by an indenter.
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This establishes a zero point.
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For the second step, a major load is then added, which indents the material.
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And for the final step, the major load is removed, while maintaining the initial load.
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The difference in depth between the first and third step is then used to calculate the hardness of the material.
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Diamond is a very hard material, which is why it is used in cutting tools.
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One of the fantastic properties of steel is its ability to be heat treated, to have its hardness tailored in different areas.
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For example, with swords you want your cutting edge to be hard but the core of the blade to be ductile.
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This means the sword can bend under pressure without breaking, while the cutting edge can resist damage.
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As always, thanks for watching.
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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C1レベルのスピーキングレッスンは、動画「Material Properties 101」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：material, stress, ductile, brittle, strength。 この動画には、シャドーイング用の文が85文、単語が1264語あります。 音声の長さは6:06です。 話す速さは速く、1分あたり約207語です。音のつながりや弱く発音される音が多くなります。 単語の82%は英語の頻出3,000語に含まれます。残りは練習の前に確認しておきましょう。
この動画の重要語彙
動画の中で特に難しい単語15語を、発音と意味つきで紹介します。
| 単語 | 発音 | 意味 |
|---|---|---|
| fracture 名詞 | /ˈfɹæk.t͡ʃʰəː/ | 骨折 |
| deform 動詞 | /dəˈfɔɹm/ | 歪める |
| tensile 形容詞 | /ˈtɛn.sɪl/ | 張力の, 伸張の |
| stiff 形容詞 | /stɪf/ | 硬い |
| graph 名詞 | /ɡɹæf/ | グラフ, 図表 |
| elastic 形容詞 | /ə-/ | エラスティック, 伸縮性の |
| absorb 動詞 | /æbˈsɔɹb/ | 吸収する |
| tuff 名詞 | /tʌf/ | 凝灰岩 |
| slope 名詞 | /sloʊp/ | 坂, 坂道 |
| axis 名詞 | /ˈæksɪs/ | 軸 |
| aspire 動詞 | /əˈspaɪɚ/ | 希求する, 熱望する |
| keyword 名詞 | /ˈkiː.wɜːd/ | キーワード |
| tailor 名詞 | /ˈteɪlɚ/ | 仕立て屋, テーラー |
| dent 名詞 | /dɛnt/ | 凹み |
| ceramic 名詞 | /səˈɹæmɪk/ | 陶器, 陶芸品 |
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 | will be uploaded · is defined · is found |
| 現在完了形 have/has + 過去分詞 — 過去の出来事が今も関係している | has occurred · we've seen · have broken |
| 関係詞節 who / which + 節 — 人や物について情報を加える | stress, which is · strength which is · material, which is |
注意したい発音
話し手はI'll, we've, wouldn'tなど、短縮形や弱形を3回使っています。聞こえたとおりの短い形で発音しましょう。
- 「sh」と「zh」の音: deformation /ˌdɛfəˈmeɪʃən/, deflection /dəˈflɛkʃən/, sectional /ˈsɛkʃənəl/, consultation /ˌkɑnsəlˈteɪʃən/
- 長い単語（アクセントの位置に注意）: deformation /ˌdɛfəˈmeɪʃən/, allowable /əˈlaʊ.əbəl/, personalize /ˈpɜː.sə.nə.laɪz/, characteristic /ˌkæɹ(ə)ktəˈɹɪstɪk/, consultation /ˌkɑnsəlˈteɪʃən/
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: brittle /ˈbɹɪtəl/, embrittlement /ɛmˈbɹɪtl̩mənt/, granular /ˈɡɹæn.jə.lə(ɹ)/, counselor /ˈkaʊnsələ(ɹ)/
- /f/ — 「フ」ではなく、上の歯と下唇で出す: deformation /ˌdɛfəˈmeɪʃən/, fracture /ˈfɹæk.t͡ʃʰəː/, deform /dəˈfɔɹm/, stiff /stɪf/, graph /ɡɹæf/
- 子音の連続 — 間に母音を入れない: distress /dɪˈstɹɛs/, brittle /ˈbɹɪtəl/, fracture /ˈfɹæk.t͡ʃʰəː/, deform /dəˈfɔɹm/, hardness /ˈhɑɹdnəs/
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。
- まず0.75倍速で一文ずつシャドーイングし、慣れてきたら通常の速度に戻します。
- 自分の声を録音して元の音声と比べます。fracture, deform, tensile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。