2013年6月19日 星期三

聽力高機率考題:Flying maple seeds

原始中文機經:

植物學。教授講楓樹的種子又被稱為 wing seed,因為長得像翅膀。說這種種子靠風力傳播,落下 時會 spin,造成對自己的 lift,像直升飛機一樣的道理。而這個 lift 可以減慢下落的速度,讓風把種子送到更 遠的地方。然後說其實動物也有很多利用這個原理,例如蝙蝠和一些昆蟲。所以認為之前一直認為植物和動 物是分別進化相對獨立的觀點被 challenge 了。最後說通過這個研究可以應用到人類科技上,例如研究新的太 空船降落系統。


原文網址:
http://www.dandydesigns.org/id59.html

1. Maple要reproduce的話,必須遠離parent trees以獲取足夠的陽光,所以必須stay airborne long enough, 本身巧妙的設計讓他可以helicopter autorotation!

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Maple seeds show great design to fulfill the needs for maple trees to reproduce. A maple tree can spread shade over a large area. In order for it to reproduce, its seeds have to get far enough away from the parent tree that the young trees will not be shaded by the parent. This means that as the seed falls off the tree it has to stay airborne long enough that it will travel for a significant distance. The very complex design of the maple seed allows it to begin its helicopter autorotation almost the instant it is released from the tree.

Maple seed's helicopter autorotation



2. 仔細看翅膀表面有葉脈,使表面粗糙增加干擾氣流,能夠使種子在空中停的更久,
高爾夫球上表面小小的凹陷也有同樣的效果!


If you look carefully at the wings, you will see that they have veins in them. The veins are concentrated on the leading edge of the wing – the part that cuts into the air. This rough texture produces beneficial turbulence and the weight of the veins improves the angle of attack of the wing. Dimples on golf balls serve a similar purpose of producing beneficial turbulence. Bird wings are also designed with the shaft on the leading edge and the feathers on the back.




3.種子的翅膀變乾後才會開始墜落,不僅可以減輕重量讓種子在空中飛的更久,乾掉的翅膀也比較容易破碎,使種子暴露使其更容易繁衍。

Maple seeds do not fall off the tree until the wings are quite dry. This has two advantages. For one thing it makes them lighter so that they will fly farther. It also makes the wing more brittle so that once they land the wing material may break away from the seed. Although the wing is important to get the seed to its destination, once the seed has landed the wing has served most of its purpose. When the seed lands between blades of grass, the wing may help the seed to stand vertically enabling it to more easily imbed into the ground.

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