Flying a kite is a common childhood pastime. Even if you haven’t done it yourself, you’ve probably at least seen it. But have you ever stopped and wondered how the fun activity actually works? What is it that keeps that colorful cloth aloft◆? If your answer to that last question is “the wind,” you are on the right track. It’s much more complicated than that, though. A kite that flutters steadily in the air with little effort from the person holding onto the string is a working example of the basic principles of aerodynamics◆, or the science of flight. Whether you are talking about a kite, a bird, or an airplane, the science is the same. The upward◆force that pushes a kite into the air and keeps it there is called lift◆. This is achieved when the air pressure underneath◆ the kite, or a wing, is higher than the air pressure above it. That difference in pressure is the result of a difference in air speeds; fast-moving air is lower in pressure and slow-moving air is higher. The design of a kite is angled◆ so that wind passing underneath it is slowed down, resulting in lift. Of course, you have to remember that the kite, though fairly light, still weighs something, so the force of the lift must be equal to a kite’s weight in order for it to fly. Once you have your kite in the air, then thrust (the force that pushes the kite forward) and drag (the force that pushes back against the kite) come into play. If you want to keep the kite steady, then these two forces must also be equal. Now, grab a kite and give it a try.
1. pastime n. 消遣，娛樂 • Watching movies is Eric’s favorite pastime. 看電影是艾瑞克最喜歡的消遣活動。 2. probably adv. 大概；很可能 • It will probably take me three weeks to read this 1,000-page novel. 看這本一千頁的小說大概要花上我三個禮拜的時間。 3. complicated a. 複雜的 • The software was complicated, so it took me quite some time to learn how to use it. 這套軟體很複雜，所以我花了好一段時間才學會怎麼用。 4. flutter vi.（在空中）飄揚；飄動 • The red flag fluttered in the breeze. 那面紅旗在微風裡飄揚。 5. steadily adv. 穩定地 steady a. 穩定的，平穩的 • The number of visitors to the winter resort is steadily growing. 這個冬季度假勝地的遊客數正穩定地增加中。 • Nathan tried to keep his smartphone steady while he was taking a selfie. 奈森在自拍的時候試著穩定他的智慧型手機。 6. principle n. 原理，原則 in principle 原則上 • I agree with you in principle; it is your method that I disagree with. 原則上我同意你，我不同意的是你的方法。 7. achieve vt. 達到；實現 achievement n. 成就 • If you work hard, you will eventually achieve your goals. 如果你努力，最後一定會達成目標。 8. pressure n. 壓力 • Cameron applied pressure on the wound with a clean cloth to stop the bleeding. 卡麥倫用一塊乾淨的布在傷口上施壓止血。 9. fairly adv. 相當地，頗 • Chad’s written English is fairly good, but he needs to improve his spoken English. 查德的英文文筆還不錯，但他需要加強他的英文口說。 10. thrust n. 推力 • Mary is calculating the thrust generated by those engines. 瑪莉正在計算那些引擎產生的推力。 11. grab vt. 抓住 • The little boy grabbed his mother’s arm and wouldn’t let go. 那名小男孩抓住媽媽的手臂不放。
1. be on the right / wrong track 思路正確／錯誤 • Joyce hasn’t solved the problem, but she believes she is on the right track. 喬伊絲還沒解決這個問題，但她認為她的方向是對的。 • These lab results show that we are on the wrong track. 這些實驗室的結果顯示我們想錯了。 2. hold onto... 抓緊……；堅守…… • The worker held onto the rope and pulled it hard. 那名工人抓緊繩子並猛力一拉。 3. slow down... / slow... down 減緩／放慢……（速度） • Please slow down your pace. I can’t keep up with you. 請放慢你的腳步。我跟不上你。 4. result in... 導致／造成…… = lead to... = bring about... = give rise to... = contribute to... • Teddy’s careless driving resulted in the accident. 泰迪的魯莽開車導致了這場車禍。 5. be equal to... 等於……；相當於…… • A kilogram is equal to 1,000 grams. 一公斤等於一千公克。 6. come into play 有影響，起作用；開始生效 • The policy only comes into play if you are absent for more than a week. 如果你缺席超過一週，這項規定才會生效。 7. give... a try 試一試／嘗試…… = give... a shot = give... a go • Just give it a try. I believe you can make it. 試看看吧。我相信你辦得到。
force n.（物理學上的）力；（自然）力；力量 • The astronauts felt the force of the Earth’s gravity when they reentered the atmosphere. 那些太空人在重返大氣層時感受到地心引力的力量。 ＊reenter [ ri`EntK ] vt.（航天器的）重返大氣層 • Not until the major earthquake struck did I realize how terrible the force of nature can be. 直到那場大地震發生，我才了解大自然的力量有多可怕。 • The truck crashed into the wall with great force. 那輛卡車猛力撞上那面牆。 --------------------------------------------------------------- 英文中還有很多單字也有「力」的意思，有時可以互換使用，介紹如下： a. power n. 力量；權力 • The power of the impact created a huge hole in the ground. 撞擊的力量在地面製造出一個大洞。 • The president has been using his power to influence foreign policy. 那位總統一直在用他的權力影響外交政策。 b. strength n. 力氣，體力；毅力 • David was so tired that he didn’t even have the strength to walk. 大衛累到連走路的力氣都沒有。 • Wendy is confident she has the strength to face the challenge. 溫蒂確信她有毅力面對這個挑戰。 c. might n.（極大的）力量，力氣 • The thief struggled with all his might to break loose from the police. 那名竊賊用盡全身力氣，想從警察手中掙脫。 d. energy n. 活力，精力 • I don’t know how Kathy is always full of energy so early in the morning. 我不知道凱西怎麼總是一大早就充滿活力。 e. vigor n. 活力，精力 • Janet turned off the TV, picked up her books, and started studying with vigor. 珍妮特關掉電視、拿起她的書，並開始起勁唸書。