Forces in water are much higher tan in air, so you see bigger effects. That said, it is likely that most of what you were observing was coming from chages in direction that occur during the "collision" with the surface. Similar result.

A really easy way to see/play with the effect of spin on a thrown object is to mess around with a beach ball. You can "spin" a ball a loong ways of course. The same trick is used in almost any ball sport - watch a free kick in football (you guys are watching aren't you?), or a baseball pitch, or tennis serve etc...

Matthias

Gard,

Yes, that does sound like Magnus effect to me.  However, Herr Magnus did his research on projectiles in a single medium.  I don't think he worked with projectiles at the interface between two media with such differing densities and viscosities.  Nevertheless, the effect is the same.

This may have been discussed already in forum, but paintball guns can be bought with barrels that curve slightly downward. The balls acquire a backspin as they skid along the top of bore. A flatter trajectory and more controlled path is achieved. Aside from  paint ball guns, more massive ammo needs more roughness  of a certain type to get good Magnus effect.
Controlled, consistant spin of any kind is a slinging challenge.  Minimal spin is preferred with some ammo for high angle distance casts.    

Tom 

     Dale,                                                                  
         You are quite right: we "modern" slingers generally get to do a lot less slinging than we would like. I wonder if there are any historical references to help us reconstruct just how common really accurate slingers were. Was this an unusual talent, or common and widespread?                                                                                    
     Thomas,                                                                               
         Yes, I seem to recall reading this about paintball guns and I think airsoft guns use the same technique. I believe this is called "hop up." Generally, I use the "Apache" technique and I suspect that this technique also imparts a spin to the projectile. After a little bit of experimentation, I found that if I hold my hand with my thumb facing backwards at the start of the slinging stroke, when my arm is almost directly overhead ( vertical ) my thumb now faces forward. Thus the release cord ( which I hold between my thumb and index finger ) is also forward and when I release, the stone "rolls" out of the pouch.
I hope to try slinging a painted stone to see if I can observe the spin, or photography with a high shutter speed might reveal this, but I simply haven't gotten around to performing this experiment yet.         
                                                                           .......Dan

Gard,
I think you have it backward.  A backspin causes the projectile to fly farther in air.  This is because the spin draws air backward over the top faster, while retarding the flow of air across the bottom, thus producing lift.  A topspin, where the ball/stone/whatever is spinning the same way as it would were it rolling along the ground, produces negative lift, and it dives into the ground.

As a stone or ball hits water, you get odd effects like you observed.  With a backspin, the bottom of the stone grabs some water and pushes it ahead, thus trying to pile up some water in front of it.  This keeps the stone on top of the water, and it skips along.  But with a topspin, the stone grabs water and pushes it backward and upward, and the stone dives into the water.

Slinger_Man_Dan,
The traditional Balearic test was to hit the slats of a gate.  Nine slats, nine casts, but I do not know the range.  I believe one might have been required to hit them in a particular order, or perhaps to announce beforehand which slat would be hit (a la billiards: "Cue ball over the rim, land on right foot of spectator wearing the fedora").

Your description sounds exactly like how I do an Apache cast, when I'm trying for a backspin.  But usually I try for a football/rifle spin, so I want the sling cords side-by-each at release, instead of fore-and-aft.  Painting a ball or stone does help.  Casting at very low power also helps, because the stone stays close enough to see, longer.

Thomas,
Tennis balls are great for practicing various spins.  The results are quite obvious.  Long ago, I slung a tennis ball underhand and it just scooted along a foot above the ground for 60 or 70 feet before dropping ... marvelous!  I've never been able to repeat that, but it is one of the reasons I keep on slinging.  Someday before I die, maybe I will be good enough I can do something like that on purpose!

Hey I've played catch with that!  The ball curves way up with underspin. It is loads of fun.


I have a question about spinning and curving projectiles.  Spinning a round object and making it curve I can understand.  Dale described it expertly.  What I don't get is when you throw something flat, like a poker card or a frisbee, the effect is the opposite.  For example, a right hander would throw  frisbee with a "backhand" style and create a clockwise spin on the object.  Such spin would make it turn to the right according to the magnus effect and I have seen it happen many times with balls and rocks but on frisbees or playing cards they curve to the left!  There must be other forces at work there?

Thanks Techstuf.  But I am still having trouble.  If the object is shaped symetrically (unlike the wings of an airplane) would it still have more lift on the advancing side?

If the advancing side of a clockwise spining flat object have more lift that means the object should tilt upward on the left side and curve to the right.  But that is not the case, I have tried with playing cards, frisbees and CDs in all three cases the right side tilt up and the objects curves to the left! ???