中級 1756 タグ追加 保存
動画の字幕をクリックしてすぐ単語の意味を調べられます!
単語帳読み込み中…
字幕の修正報告
Airplane jet engines have gotten bigger and bigger over time - and it’s not just because
planes are getting bigger: the Airbus A350 is a smaller plane than the Boeing 747 but
has bigger engines. The reason? Bigger engines are simply more efficient, up to a point.
Modern jet engines actually consist of two propulsion systems working together: the jet
core, which provides the power and a small amount of thrust, and the fan, which is just
a big propellor driven by the jet core that provides most of the thrust.
Pure jet engines can be incredibly powerful (which is why they’re used for fighter jets),
but they’re also horribly inefficient because they shoot out their exhaust at super high
speeds, which equates to huge amounts of kinetic energy, since kinetic energy is proportional
to the speed squared, so accelerating exhaust to twice the speed takes 4 times the energy.
In exchange for power, they literally blast energy away as a bunch of hot air.
Of course, you do have to shoot some air out of the back of an engine to generate thrust,
but it doesn’t have to have lots of energy. Instead of accelerating a little bit of air
a lot, you can achieve your desired thrust by accelerating a lot of air a little bit
- you get the same momentum boost but save a ton of energy.
Essentially, if you make an engine too small, it has to accelerate the air so much as to
be a waste of energy – kind of like using a machine gun to propel your car. But if you
make the engine too big, then it starts to cause too much drag. An ideal engine is somewhere
in between – rough estimation puts the ideal engine somewhere around 4 meters in diameter,
which is just slightly bigger than the current largest engines.
So you can expect jet engines to continue growing in size... but not forever.
I’d like to thank Audible.com for supporting this video. As you may have heard, Audible
has audiobooks of all sorts, including fiction, non-fiction and periodicals. You can try Audible
free for 30 days by going to audible.com/minutephysics, and if you do so I recommend the book Ender’s
Game by Orson Scott Card, it was one of the pivotal sci-fi novels I read as a teenager
and I can’t recommend it enough. Remember, the enemy’s gate is down. And you can try
Audible free for 30-days by going to audible.com/minutephysics.
コツ:単語をクリックしてすぐ意味を調べられます!

読み込み中…

なんで飛行機のエンジンは大きいのか(Why Are Airplane Engines So Big?)

1756 タグ追加 保存
Ken Lo 2017 年 1 月 26 日 に公開
お勧め動画
  1. 1. クリック一つで単語を検索

    右側のスプリクトの単語をクリックするだけで即座に意味が検索できます。

  2. 2. リピート機能

    クリックするだけで同じフレーズを何回もリピート可能!

  3. 3. ショートカット

    キーボードショートカットを使うことによって勉強の効率を上げることが出来ます。

  4. 4. 字幕の表示/非表示

    日・英のボタンをクリックすることで自由に字幕のオンオフを切り替えられます。

  5. 5. 動画をブログ等でシェア

    コードを貼り付けてVoiceTubeの動画再生プレーヤーをブログ等でシェアすることが出来ます!

  6. 6. 全画面再生

    左側の矢印をクリックすることで全画面で再生できるようになります。

  1. クイズ付き動画

    リスニングクイズに挑戦!

  1. クリックしてメモを表示

  1. UrbanDictionary 俚語字典整合查詢。一般字典查詢不到你滿意的解譯,不妨使用「俚語字典」,或許會讓你有滿意的答案喔