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  3. Everyone knows a stone bounces best on water if it’s round and flat, and spun towards the water as fast as possible. Some enthus

Everyone knows a stone bounces best on water if it’s round and flat, and spun towards the water as fast as possible. Some enthus

admin2019-06-20  5
问题     Everyone knows a stone bounces best on water if it’s round and flat, and spun towards the water as fast as possible. Some enthusiasts even travel to international stone-skimming competitions, like world champion Jerdone Coleman-McGhee, who made a stone bounce 38 times on Blanco River, Texas, in 1992.
    Intuitively, a flat stone works best because a relatively large part of its surface strikes the water, so there’s more bounce. Inspired by his eight-year-old son, physicist Lyderic Bocquet wanted to find out more. He tinkered with some simple equations describing a stone bouncing on water in terms of its radius , speed and spin, and taking account of gravity and the water’s drag.
    The equations showed that the faster a spinning stone is travelling, the more times it will bounce. To bounce at least once without sinking, Bocquet found the stone needs to be travelling at a minimum speed of about 1 kilometre per hour.
    The equations also backed his hunch(直觉)that spin is important because it keeps the stone fairly flat from one bounce to the next. The spin has a gyroscopic(陀螺的)effect, preventing the stone from tipping and falling sideways into the water.
    To match the world record of 38 bounces using a 10-centimetre-wide stone, Bocquet predicts it would have to be travelling at about 40 kilometres per hour and spinning at 14 revolutions a second. He adds that drilling lots of small pits in the stone would probably help, by reducing water drag in the same way that dim pies on a golf ball reduce air drag.
In order to make a stone bounce best on water, one needs to______.
选项 A、find a big, round stone
B、make the stone spin as fast as possible
C、reduce the spin of the stone
D、do some complicated mathematical equations
答案B
解析 根据文章的第一段第一句可知，旋转越快，石头弹跳越好。故选B。
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