Sunday, June 19, 2005

Weird Science: Great Sailing Balls

Four! Ever hear that behind you on the golf course, followed shortly by a four-letter F word of your own as that long drive nearly hits you? Why is it that golf balls can travel so far anyway - several hundreds of yards? Today, briefly, we will examine those balls to see why.

The first golf balls were actually smooth. But golfers of long ago, as proficient today with four letter F words as we are, found that scuffed up balls traveled farther than new smooth ones. They quickly began to hammer small dents into new balls to make them travel farther. Strange but true fact. But why is that so?

Well it has to do with aerodynamics and boundary layers. You see the golf ball must push its way through the air as it sails toward the green, water, sandtrap, back of another golfer’s head, or the nearby interstate - depending on your skill level.

And a ball traveling through air has a boundary layer of air surrounding it - a skin if you will of air clinging to the ball. There are two types of boundary layers. One is turbulent and the other is laminar or smooth. A dimpled golf ball sailing through the air has a turbulent boundary layer while a smooth ball has a laminar one clinging to it.

Now, a golf ball with turbulent boundary layer will cause less of a wake (like that of a boat in water) than a smooth ball. And this wake effect, dealing with pressure differentials on the front and back of the sailing gall, makes all the difference in how far it will go. The dimpled one wins easily, able to travel twice the distance as a smooth one.

So, if dimples are so great, how many is too many or not enough? Well, there is no actual ideal number, but the number of dimples that work best comes in between 300 to 500. Way more than Shirley Temple. And the more dimples you try to put on a golf ball past 500, the closer the golf ball gets to becoming smooth and you defeat the effect.

So, the next time you are playing with your balls, you will have a better understanding of why they can sail so far after you whack them. . . .

Ummm, that could have been worded better.
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