[OT] Simple math considered physics; turns out it's fun, not harmful

Jim Kuzdrall gnhlug at intrel.com
Wed Nov 21 22:40:25 EST 2007


On Wednesday 21 November 2007 17:51, Greg Rundlett wrote:
>  He said if I have some friends who know physics I could figure out
> how fast that is in the big leagues.  I'm not making fun of the guy,
> but physics isn't involved in solving the problem, just regular math.

    Actually, it is a physics problem.  Assuming the ball velocity is 
measured at "home plate", the ball is likely to have left the pitcher's 
hand at a considerably higher speed than it has at the end of its 
travel.

   With the Reynold's number for the baseball and some well accepted 
flow models, the "flow regime" can be determined.  I would guess it is 
in the velocity cubed region.   That means drag forces are proportional 
to velocity cubed, and thus the speed may vary considerably during its 
travel.  Again, subject to a rather straight forward computational 
confirmation.

    If the ball is slowing down significantly, it must be going quite a 
bit faster at 33 feet, and even faster at 60 feet.  Which means that 
the travel time (batter response time) is shorter for a 96mph pitch 
than you calculated by the linear speed approximation.  In fact, 
intuitively the 70mph guess might be about right.

    Anyway, congratulations for turning to some math (and physics) for 
an initial guess.  Very often, particularly in engineering, such 
approximations are good enough to whittle choices down to only one (or 
none), making the more sophisticated computation unnecessary.  And it 
gives more insight than a blind guess.  And fun.

    The difference between pure math, applied math, and physics is 
probably too OT for this forum.  But interesting.

Jim Kuzdrall


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