One of our users, JSS, has commented on a topic on the site.  Because the comment was of such high quality in explaining how airflow over and through a wiffle ball works, I decided it needed it’s own post.  Thanks JSS, for making a difficult to understand subject a little easier for everyone.  Here’s the comment in it’s entirety.

Have you considered cutting/scuffing the side of the ball without the holes? You can get a slider to break about 4-6+ feet that way, as you induce a ‘slippery’ turbulent boundary layer to form on the side without holes. Batters think the pitch will go BEHIND them, then it crosses over and hits the zone. I used to aim at a spot (fence post) 3 feet behind the batter’s head when throwing it to hit the strike zone. The wiffle ball breaks toward the holes at slow speeds due to turbulence induced by the holes so the ball breaks toward the holes at slow speeds. At faster speeds, the ball will break away from the holes as the air flowing around the solid side sticks to it more (boundary layer theory), like the upper part of a wing, and deflects the ‘wake’ away from the direction it breaks. What you do by scuffing is lower the speed at which the ball will change from breaking towards to away from the holes, and the air “sticks to” the scuffed side even more efficiently (like the little traingular vortex generators on the leading edge of aircraft wings), causing a larger break distance, but the penalty is some speed is bled off from all of that air being deflected, no free lunch.

Here is the crazy thing: The ball size has everything to do with how fast the transition speed is, because of Reynold’s Number. Buy some wiffle junior balls, and some wiffle king balls (softball size). The wiffle kings will break away from the holes at a much slower pitch speed. The wiffle junior needs an even faster pitch than the regular wiffle ball to break away from the holes. The curious thing about the wiffle junior is that if thrown hard enough, it will break away from the holes for the first part of the pitch (until about 15 feet from the batter), then CHANGE direction and break towards the holes as it slows down. Really creepy pitch. A slider thrown by a RHP will appear to be unreachable at first to a right handed batter (break far out of reach outside), then just as the batter has made the decision not to swing, it will change direction and tap the strike zone, infuriating the batter. You can of course scuff the solid side of the junior balls to reduce the transition speed, making them act more like an unscuffed regular ball.

The Wiffle Kings can be thrown harder due to the extra mass; they carry further and keep their speed better, and the transition speed is very slow, like 25-30mph, then it starts breaking away from the holes. They can be hard to hit, and will actually dent the yellow wiffle bats. They curve less, because they are heavier, unless scuffed almost paper-thin, but then you lose the speed/momentum advantage.

We use the junior balls because they break towards the holes at medium pitch speeds (small backyard with tall ‘fences’), and we use lighter wooden bats: fungo bats (17-22 oz), the marucci stick, and the markwort corkball bat. It makes for a pretty fun time, mound is 41 feet from strike zone, about 38 feet to home.

JSS