Angels or SFO/aerodynamics of a curvebal

[bigr]

We studied this in my fluid dynamics class in college.

corky is on the right track, however the conclusion is wrong.

and enigma is essentially right. the curve ball you see on TV is for the most part an optical illusion. however there are aerodynamic forces at work.

a better illustration of a curve ball is the "tennis ball".

what causes a ball to "curve" is the interaction of the "boundary layer" on the ball interacting with the relative wind.

if you have ever hit a tennis ball with back spin then you notice that the ball will "float" and probably be out of bounds. however, for those of you old enough to remember Bjorn Borg and Guilermo Villas, they both hit the tennis ball with tremendous "top spin". this made the ball "dive" into the court.

why does this happen?

this happens because of the boundary layer of air around the ball.
what is the boundary layer? it is a microscopic thin layer of air that "attaches" to the ball. this also happens to an airfoil and causes drag. engineers have been trying to reduce this for years and i won't go into it.

the boundary layer spins with the ball. think of the boundary layer as a microscopic layer of air that adhears to the ball and spins with it. thus for a tennis ball with top spin, this creates an interaction between the boundary layer of air and the relative air that the ball flys thru. this creates a greater pressure differential at the top of the ball (forward of top dead center of the ball). at the bottom of the ball the boundary layer has less relative velocity with the "relative wind" of the ball flying thru the air. thus this is a lower pressure area and the tennis ball is "pushed downward" if it has top spin. this is an aerodynamic force and has nothing to do with rotational momentum or gyroscopic forces.

therefore, a curve ball thrown that rotates clockwise (looking down) will curve to the right.

check out "aerodynamics for naval aviators". it explains this in terms of airfoils.

 

[TurboS7]

If there is no rising fast ball then why do I have to raise my mitt up 8" at the last second to catch my son's fastball. (He throw 90+ MPH) I used to have to do the same with my Dad(he used to pitch for the Brooklyn Dodgers) his fast ball was fast, real fast.

 

[bigD]

Hmmm...seems to me we're all pretty much saying the same thing here.

According to my simulation, a typical curveball has a horzontal displacement of around a foot or so. Of course this is all dependant on the pitch speed, ball rotation speed, etc... I haven't gotten the assignment back yet, so I'm not ABSOLUTELY sure if my equations of motion and boundary conditions are right, but I think they are. The code to solve the differential equations is definitely correct, though. It's been tested in other situations. To be fair, I'm not worrying about the decay of rotational speed because it's pretty negligable over the time it takes the ball to travel from the pitcher to the catcher.

Turbo7 - I'm not a baseball player, and like I said above, maybe my math is simply incorrect, but the Magnus force seems to be roughly a third of the force of gravity. So in the case of a fastball, the rate of decent of the ball would be slowed, but the force would never be large enough for the vertical displacement to be negative (upwards) in relation to gravity. I think what's happening is that you're placing your catcher's mitt at a location where you'd expect the ball to be on a normal pitch, and finding that the ball doesn't drop as much as you expected it to - so you have to raise the mitt up a bit. My code shows a fastball of about 90mph to drop a little over a foot.

 

[TurboS7]

That is what makes the whole thing totally facinating. How can we hit a ball that is travelling 90MPH, dropping one foot and moving one way or the other, especially when we can't even see the ball the last couple of feet to the bat. The "break" is dependent on the diffrence of the vector force of the throw vs. the aerodynamics of the ball. Wonderful game last night.