A disc-shaped stone has to be tossed at an angle of 20 degrees to achieve the maximum number of bounces across water.
将碟状石子以20°的角度投出可以打出最多次数的水漂。

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.
英国科学家巴恩斯·威利斯发明了弹跳炸弹，受其启发，研究人员解释了石子、玩具甚至炮弹在水面弹跳这一现象背后的复杂物理原理。

Naval gunners as far back as the 18th century bounced cannonballs as a military tactic.
上溯到18世纪，海军炮手将炮弹弹跳作为一种军事战术。

'Designed to breach German dams, the weapon skipped over the water surface to avoid undersea torpedo nets.'
“为了破坏德国大坝，炸弹在水面上弹跳以避开水下鱼雷网。”

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》写到，如今，随着玩具球的出现，打水漂已经变得更加容易驾驭，多次弹跳也变得简单了许多。

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.'
研究人员说：“这些球体由弹性材料制成，其高依从性或者说易变形的特点为水漂现象带来了一些有趣的变化。”

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.
不过，转动手腕、体侧投出，老老少少的人们用石子打了千百年水漂，目标只有一个，就是让石子在水面的弹跳次数尽可能多。

The world record, according to the Guinness Book of Records, is 88 skips set this year by an American called Kurt Steiner.
据《吉尼斯世界纪录》记载，打水漂的世界纪录是88次弹跳，由美国人库尔特·斯坦纳于今年创造。

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.
特拉斯科特教授说打水漂的技术基于投掷者选取的投掷角度，就碟状石子而言，最理想的投掷角度接近于20°。不过，投掷的物体越重，角度应该越小。

He said: 'Spheres are generally harder to skip than discs. In fact, previous research suggests an upper bound on the initial course angle 18°.
他说：“一般来说，与碟状物体相比，球体的弹跳更难实现。事实上，前人的研究表明，投掷角度的上限是18°。”

'Thus for steel cannonballs, skipping can only occur for angles shallower than seven degrees.'
“因此，对于钢制炮弹而言，只有投掷角度小于7°时才有可能产生弹跳。”