打水漂祕籍 20°角投擲效果最佳

A disc-shaped stone has to be tossed at an angle of 20 degrees to achieve the maximum number of bounces across water.

將碟狀石子以20°的角度投出可以打出最多次數的水漂。

Inspired by English scientist Barnes Wallis, who invented the bouncing bomb, researchers have described the complicated physics behind the water-skipping behaviour in stones, toys and even cannonballs.

英國科學家巴恩斯·威利斯發明了彈跳炸彈，受其啓發，研究人員解釋了石子、玩具甚至炮彈在水面彈跳這一現象背後的複雜物理原理。

Naval gunners as far back as the 18th century bounced cannonballs as a military tactic.

上溯到18世紀，海軍炮手將炮彈彈跳作爲一種軍事戰術。

'Designed to breach German dams, the weapon skipped over the water surface to avoid undersea torpedo nets.'

“爲了破壞德國大壩，炸彈在水面上彈跳以避開水下魚雷網。”

Writing in Physics Today, they say water skipping has returned to more docile roots of late with toy balls that make it much easier to achieve multiple hops.

《今日物理》寫到，如今，隨着玩具球的出現，打水漂已經變得更加容易駕馭，多次彈跳也變得簡單了許多。

The researchers said: 'Those spheres are made of an elastic material whose high compliance - or ability to readily deform - introduces some interesting changes to the skipping phenomenon.'

研究人員說：“這些球體由彈性材料製成，其高依從性或者說易變形的特點爲水漂現象帶來了一些有趣的變化。”

But, with a side throw and flick of the wrist, people young and old have been skipping stones across water for thousands of years with the object of getting as many bounces as possible.

不過，轉動手腕、體側投出，老老少少的人們用石子打了千百年水漂，目標只有一個，就是讓石子在水面的彈跳次數儘可能多。

The world record, according to the Guinness Book of Records, is 88 skips set this year by an American called Kurt Steiner.

據《吉尼斯世界紀錄》記載，打水漂的世界紀錄是88次彈跳，由美國人庫爾特·斯坦納於今年創造。

Professor Truscott said the skill depends on what angle the thrower chooses to hurl an object at, with the optimal for disc-shaped stones close to 20°. But the heavier the object, the flatter this should be.

特拉斯科特教授說打水漂的技術基於投擲者選取的投擲角度，就碟狀石子而言，最理想的投擲角度接近於20°。不過，投擲的物體越重，角度應該越小。

He said: 'Spheres are generally harder to skip than discs. In fact, previous research suggests an upper bound on the initial course angle 18°.

他說：“一般來說，與碟狀物體相比，球體的彈跳更難實現。事實上，前人的研究表明，投擲角度的上限是18°。”

'Thus for steel cannonballs, skipping can only occur for angles shallower than seven degrees.'

“因此，對於鋼製炮彈而言，只有投擲角度小於7°時纔有可能產生彈跳。”