Open hand or not

Originally posted by Kim Tarnower Not the thumb tip and fingertip touching, but the thumb held alongside the pointer finger in a flat position. I think the idea is that a flat "paddle" shape of the hand (whether fingers held together or slightly apart) is better than a cup shape. You explained the point perfectly. Thanks George

and all this time I thought that i could swim :) but seriously though I get the idea. Thanks for the thoroughly detailed discussion.

I read somewhere about the angle of the hand having alot to do with how much water can be 'trapped' at the the beginning of each stroke. We were taught 20 years ago to keep the palm outward to initiate a high elbow on the entry. I've seen some of the latest college phenoms using more of a scooping action to the catch. This was even more evident with the sprinters. Does anyone know if this is what coaches are promoting these days?

Lindsay, you are missing something major here. Your actual velocity = Force you apply to the water - Drag ( all of the combined drag forces that act on your body ). Your body may in fact not accelerate in actual velocity ( relative to when you push off the wall ) but F=MA is in effect with each propulsive phase of your stroke. If it was not you would slow to a stop in a few metres and never move again ! Force is generated by hand and arm and the fore-foot, during the kick. It is also obvious from the equation that the hand has to Accelerate during the arm movement to maintain and increase the force applied. That is the hand moves from almost at rest ( hand entry - catch) to moving rapidly at the end of the arm action. This movement, though, has to be a controlled acceleration as Fluid Dynamics will punish hasty movements by rapidly increasing drag and premature shedding of the propulsive vortex. Look in Cecil Colwins "Breakthrough swimming" for detailed info on this. Smooth, controlled application of force, while minimising drag and conserving momentum is the best way of swimming. Learning how to maintain this at high speed is the tricky part ! We don't know very much about how swimmers actually move through the water. Previous studies have not been set up very well. The dominant theory in the last 30 years was of Lift dominated propulsion. This lead to talk of "sweeps " etc. One of the main studies for this involved a model of a hand on a stick, suspended in a steady flow and the resultant forces were analysed ! In fact lift forces are quite unimportant in the conditions of " unsteady flow " that apply in actual swimming as the boundary layer cannot attach itself to the hand properly to allow lift forces to operate ! Until we can do studies where sensors are attached to swimmers and analysis is based on what occurs when they actually move in the water then we will not know for sure what is going on.

You explained the point perfectly. I consider that high praise indeed, coming from you, George! :cool: Thanks! :)

Hey Mark, you're right, but I don't think I was being picky, while a large paddle wheel will produce an approximation of constant velocity straight line motion the quoted description of how F=ma applies to swimming was totally wrong. After a quick read of the paper on propulsion and vortices it isn't clear to me that the vortices produce propulsion, it seems to me that are a side effect of propulsion that might be useful in analyzing the efficiency of the propulsive movements, if some way to observe the vortices can be figured out. Gareth, you are probably right that we won't reason our way to a record time, I was just curious if there was anyone here with a more solid knowledge of fluid dynamics than my own that might enlighten me on what the dominant forces are. I admit that I get irritated when I read technical material that seems incorrect, and several sections of Breakthrough Swimming drove me up the wall. The thing I did find useful was the section on the importance of timing, even though Colwin somewhat mashed up the concept of momentum. Realizing the importance of timing and avoiding loss of momentum did actually help me understand and improve my butterfly stroke.

Originally posted by LindsayNB but I don't know quantitatively what the relative contributions are. Anybody out there that is still up on their fluid dynamics? Check out any of Colwin's books, there are chapters on fluid dynamics and technique. The principle to remember is that it is more efficient to move a large mass of water slowly, than to move a small mass of water quickly.

Newton's Law, 1, 2, 3, all come into play, and I am sure that many other things come into play. When the new technology comes to us we shall be able to fly through the water and I may not be here to see it in my time. George.

you guys lost me. Thats all too complicated. This brought up a question though; Is the hand more relevant than the forearm?

I don't doubt that F=ma plays a role in swimming, after all my original question was what the relative contributions of force from accelerating water are versus force from viscosity/drag. The problem with the passage I quoted was that it got the terms all wrong and the relative contributions all wrong. The passage defined m to be the mass of the swimmer and a to be the acceleration of the swimmer. I think we would all be happy if we could maintain the speed we had coming off the wall right? To maintain velocity is to have zero acceleration and therefore F=ma tells us zero force is required! In reality to maintain speed the propulsive force exerted by the swimmer must be equal and opposite to the drag forces thereby summing to zero. In the original passage the author said: "Although it is not totally accurate because of the friction of the water it does explain the basic force a swimmer must exert." This is completely untrue for a swimmer moving at constant velocity (acceleration is zero), the "friction" (really drag) is the basic force not the inaccuracy! One of the problems I have with a lot of the swimming literature is that it isolates various factors without looking at relative contributions. You invariably find explanations of the bernoulli effects as they apply to foils but anyone with a passing familiarity with these can tell you that the hand makes a hopeless foil and that if there is any effect at all it is insignificant. All you have to do is go to the pool and move your hand back and forth in the water to realize that you aren't going to do a 30s 50m moving your hands back and forth. You can generate some force by moving a hand laterally at an angle, but the force will be a fraction of moving the same hand straight back. I have to say that propulsive vortexes are something I'm pretty sceptical about, I have a hard time believing they make any significant contribution to propulsion (to tell the truth the only discussion of propulsive vortexes I remember was wrt the dolphin kick, which I didn't buy at all, perhaps there is a more convincing case elsewhere but I am skeptical). I only had one course in fluid dynamics in my undergrad engineering days but I can't help but feel that my prof. could have sorted through most of the literature and pointed out what made since and what was foolish and what would require experimentation to determine. I suspect that a lot of it could be dismissed without the need for any experiments.