walter wrote on Aug 6
th, 2009 at 10:22pm:
Still impressive Aussie! Do you usually hole tennis balls that you're going to use for sling ammo?
walter
Not deliberately but I have yet to find a tennis ball that doesn't eventually rupture from the pounding it gets when thrown repeatedly against a hard wall. The ball in the picture was already fairly badly ruptured and due to be thrown out. If the ball was still intact I doubt it would have been able to squeeze down enough to stay in the crack which is only around 3/4" wide. Still the photo looks good.
Superficially tennis balls appear to be constructed like baseballs, ie. from two figure 8 like halves. In fact only the felt is applied that way. Underneath is an ordinary hollow rubber ball moulded in two hemispherical halves which are welded or glued together. It is this joint which fails. Quality balls will last several hundred or even a thousand shots; the cheapies will sometimes rupture on the first. Still if you only throw them so they land on grass they're OK, but for throwing against a returning wall reasonable quality is required.
BTW an easy way to increase the weight of a tennis ball is to inject some water into it with a hypodermic needle. It also reduces the amount of spin as the water inside can't be spun up by the release much the same as it's virtually impossible to spin a raw egg. Can be of use if you're getting a lot of distance robbing topspin.