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"  There&amp;#039;s no better way to beat the stifling summer heat than to spend a day at the pool\u2014catching rays, cooling off in the water and, of course, impressing family and friends with a soaring, splashy cannonball. But no matter how impressive your jump, inevitably a larger, or more skilled, cannonballer will take to the pool with a louder, bigger and wetter splash. It doesn&amp;#039;t have to be that way. To make the biggest splash, all a jumper needs is a little fluid dynamics know-how, a high-speed photography cheat sheet and some practice.  What Happens During a Cannonball The first physics lesson is simple: To get the best splash, you must act like a sphere.  &amp;quot;If you&amp;#039;re doing a cannonball, it is very similar to when you drop a sphere in the water,&amp;quot; says Tadd Truscott, a professor of mechanical engineering at Brigham Young University who studies the interface between air and water and the behavior of solid objects at that interface. As soon as a body hits the pool&amp;#039;s surface, water is displaced to make room for the plunging object. Since that water has no other place to go, it shoots upward and outward. In the case of a sphere, high-speed cameras capture an image of a crown-shaped ring of splash surrounding the border of the object. This initial splash, sometimes called the radial jet, is very fast\u2014it leaves the water at 20 to 30 times your impact speed, Truscott says. &amp;quot;That&amp;#039;s what hits the people on the deck.&amp;quot; (For pics of a sphere hitting water, see our high-speed splash photo gallery) At that point, things underwater start to get interesting. As a body descends, an air cavity forms in its wake. This cavity is about the size of the object and as it descends in the water it becomes an hourglass shape.  Immediately after the cavity forms, the pressure from the water surrounding it causes it to collapse inward from the perimeter. Eventually the cavity completely collapses at one point, called the pinch-off location. After the collapse, the water that is still rushing inward to fill the cavity escapes upward, and, assuming that the body hit the water straight on, shoots straight up and out of the water. &amp;quot;The &amp;#039;kerplop!&amp;#039; and the spray that comes out at the end is from this collapsing event,&amp;quot; Truscott says. Physicists call this the jet.  &amp;amp;gt;  How to Make the Biggest Splash In terms of water volume launched from the pool, the jet is most influential in making a big splash. Overall size depends heavily on impact speed, says Stephan Gekle, a professor of physics at the University of Twente in the Netherlands. Gekle has run similar experiments to Truscott&amp;#039;s, using disks instead of spheres. &amp;quot;The jet size depends also on the impact speed, but here the object shape is very important,&amp;quot; Gekle says. The more rounded, the object (or human) is, the larger the jet will be. Weight is also a factor, since heavier objects will form deeper air cavities. What matters most underwater is the size and shape of the cavity formed. The larger the cavity the more water must rush to fill it\u2014and the straighter the cavity, the larger the portion of water that leaves the pool. &amp;quot;That&amp;#039;s one of the reasons you get a much better jet with a cannonball than with a belly flop,&amp;quot; says Nathan Keim, who researches fluid dynamics at the University of Chicago. &amp;quot;You create a cavity that is much more symmetric and deep. Because it&amp;#039;s symmetric you&amp;#039;ve set things perfectly for when that water rushes back in to fill the cavity,&amp;quot; Keim says. &amp;quot;It gets focused, so it comes in from all directions, and then has no choice but to go up.&amp;quot;  Another way to increase splash is to change your external chemistry. Truscott does drop tests with both hydrophobic (water-resisting) and hydrophilic (water-loving) spheres. Splash size increases as the degree to which an object is hydrophobic increases, and decreases as hydrophilicity increases. &amp;quot;Humans in general are hydrophobic,&amp;quot; Truscott says. But you can become even more hydrophobic by wearing brand-new clothes, or a hydrophobic wetsuit or water polo suit. Alternatively, you could coat your body in a hydrophobic substance such as Vaseline or soot. Of course, if you get onto the high-dive covered head-to-toe in Vaseline, your ability to impress family and friends may be significantly diminished. "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.popularmechanics.com/adventure/sports/a5967/physics-of-cannonball-splash/>