[email protected] (David E. Belcher) wrote in message
news:<
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>
[email protected] (PotatoSmack) wrote in message
> news:<
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> > I was contemplating the dimples on a golf ball and the ridges on a Frisbee. I noted that a
> > little turbulence was a good thing. Hence to make myself more aerodynamic on the bike I will
> > shave the front of my legs and leave the back of my legs hairy. What effect will this have.
> > Comments and opinions please.
>
> Well, as far as the golf ball goes, I recall reading [1] that a team of scientists wondered why
> golf balls are dimpled in the first place, so they decided to experiment with smooth golf balls.
> End result - they found that the traditional dimpled ball is *more* aerodynamic; apparently the
> little dimples break up the air flow and reduce drag.
>
> David E. Belcher
>
> Dept. of Chemistry, University of York
Determining why golf balls are dimpled does not require experimentation, it more requires the lack
of experimentation. The dimples are put on golf balls to generate aerodynamic lift. I think a team
of scientists should wonder why dimples are put on golf ball to generate aerodynamic lift when in
fact a golf ball used for its intended purpose does not generate lift at all. This will take some
simple experimentation.
The dimples on the golf ball can certainly reduce the dynamic drag on the ball in flight. The real
reason golf balls are dimpled is to increase surface or friction drag. This is what causes the
Magnus effect also called Magnus lift. Surface drag on a spinning ball is reflected in a toque force
that apposes rotation. If the surface drag on one side of the ball were to become greater than the
surface drag on the opposite side a more linear force is produced. The uneven surface drag around
the ball is brought about by the golf balls linear motion. I have never seen a paddleboat with a
smooth cylinder for a paddle wheel but that would be a good experiment. Try smooth, dimpled and
paddled. The forward linear force generated by the paddle wheel is drag its also thrust. You do not
want to increase the surface drag too much on a spinning golf ball because it would more quickly
lose its spin. And believe it or not the Magnus effect is based on the fact that the ball is
spinning even though when determining the aerodynamic force that causes it the fact that the ball is
spinning is totally ignored.
