Open hand or not

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! Lindsay, are you confusing Velocity with Force ? F=MA is Zero and still move forwards can only be true in a Vacuum, and that after an initial propulsion. The actual velocity of the swimmer could be expressed as the sum of: F=MA ( of swimmer ) minus F ( where F is force of total Drag ) The water pushes back almost as strongly as we push against it. If there is no force exerted by the swimmer we STOP. The force exerted must be greater than the total drag to Accelerate or Equal to total drag to move at a constant velocity. The original question bout hand position is also well addressed in Colwins book. In short the larger the surface area the better, and fingers should be forward of the palm to hold pressure against the water rather than be bent backwards, which allows pressure to slip. :)

Originally posted by u352 you guys lost me. Thats all too complicated. This brought up a question though; Is the hand more relevant than the forearm? In swimming everything is revelant. Hand, forearm, kick, body roll, start, turn, guts, etc. etc. George

Hey y'all. Try this while you're sitting at your computer. Put an elbow on the table and study the hand a little while the forearm is in the up position. If you make a fist, the hand area is as small as it can be. If you open the hand and keep four fingers closed, but relaxed, most of us have a cup shaped hand; if you bring in the thumb and close it next to its neighbor the cup becomes more pronounced. Also, the more relaxed the joints are the deeper the cup becomes, approaching the fist configuration. Doc Counsilman, in his SCIENCE OF SWIMMING announced his results of his hand studies to show that the cupped hand was less effective than that held straight and that the spreading of fingers was found to be not detrimental. Also the wrist should be straight, especially not hyperextended. Now, if you'll lay your hand lightly, palm down, on the table, then press down on the knuckles with the fingers of the other hand, you'll see how much bigger an area your hand covers. Your fingers are spread apart, some more than others, seeming to be the best you can do with what you've got. The question here is whether or not it is worth the extra energy and attention to make the hand thus, bigger. And, yes, how much bigger, since we can actively spred the fingers much more! I think you'll find that swimming with closed fists, will make your time slower by ten percent, and your stroke count per pool length will increase by ten percent. Thus, the open hand, cupped as little as possible, extended with a straight wrist, is the best appendage to be using in swimming. And, since Valhallan brought up, and rightly so, the subject of "elbows up", Doc Counsilman would point out that this can be achieved in the crawl stroke automatically by the thumb first hand entry. If the hand entry is "pinky first" the bending of the elbow to initiate the stroke creates the dreaded "dropped elbow", correctable only by a contortionist.

Originally posted by LindsayNB Ouch! In the case of a swimmer they start each length travelling faster than they can maintain by swimming so their is no forward acceleration involved after you leave the blocks or wall, i.e. all the force is used to overcome friction. F=ma tells you nothing about the force you have to exert except for on the blocks or pushing off the wall! Would it not be easier if we could swim through the air like I used to dream when I was younger. George

Originally posted by geochuck Would it not be easier if we could swim through the air like I used to dream when I was younger. Air would certainly be easier to glide through, but it would be very hard to accelerate in! I still sometimes have dreams where I levitate or swim in the air. Luckily physics doesn't apply to dreams! :)

Um, no, I don't think I am confused, but then if I were I probably wouldn't think I was... The F in F=ma equation can be elaborate to: F = the sum of all forces acting on the body the main components of the sum are F(p) the propulsive forces exerted by the swimmer F(d) the drag forces exerted by the water on the body then F = F(p) + F(d) noting that F(p) and F(d) will have opposite signs. if the swimmer has constant velocity then a = 0 and ma=0 so F(p) + F(d) = 0 or F(p) = -F(d) If the swimmer is exerting no propulsive force then F(d) = ma and a = F(d)/m with drag force F(d) being exerted in the opposite direction of movement the swimmer will decelerate. All of this is only to say that the original passage was misleading, F=ma does apply but in terms of understanding how much propulsive force you need to apply it is more useful to go to the direct equation for a swimmer moving at constant velocity F(p) = F(d) as swimmer generated acceleration is only involved when pushing off the blocks or wall. Putting my original question another way, I wonder what the ratio is of drag forces acting on the hand as it moves backward is relative to the force due to the inertia of the water that is being accelerated backward. My recollection is that the orginal nonsense about lift forces came out of the observation that the hand left the water at a point ahead of where it entered, therefore it couldn't be moving water back to achieve propulsive force and therefore propulsion had to be explained by sculling motions. As a thought experiment one can image a paddleboat with paddle wheels moving at a constant velocity. The boat can move forward without requiring the paddles to accelerate. The question is how much of the propulsion is due to the paddles accelerating water backward and how much is due to the drag on the paddles as they move backward.

Originally posted by knelson I'm going to argue this might be exactly the behavior you DON'T want. Your hand is getting knocked back due to the increase in drag. It seems to me you want to minimize drag on the entry part of the stroke--you want your hand to slice through the water. I feel the "pull" part of the stroke which dictates the forward motion, would be the most important factor of the arm stroke itself. It would seem one would want to sacrifice the increase of drag upon entry to gain a better pull, for the better part of the stroke. Look at the percentage of time spent at the entry point of the stroke, VS the percentage of time spent actually pulling, It would seem apparent that one would want to focus more on the actual pull rather than the entry style. Granted both are important, one just seems to weigh a bit heavier. I can only speak for myself, but I know when my arm enters the water, it enters very streached out and long. Once my hand hits the water I begin my pull. There is very little time or energy spent moving my hand through the water forward before the actual pull. It seems my hand position at entry has no real effect on the performance of my stroke.

Next time you are in a car, open your window (while driving, lol) stick you hand out with a cuped shape, as some would use during swimming. Then spread your fingers apart just a little, you will notice that you catch a great deal more air and your hand will be knocked back. This is a experiment I make my swimmers try. I feel the fingers open method works very well. Many big name swimmers use this method. Keep an eye out at the games.

Originally posted by ced357 Next time you are in a car, open your window (while driving, lol) stick you hand out with a cuped shape, as some would use during swimming. Then spread your fingers apart just a little, you will notice that you catch a great deal more air and your hand will be knocked back. This is a experiment I make my swimmers try. I feel the fingers open method works very well. Many big name swimmers use this method. Keep an eye out at the games. I'm going to argue this might be exactly the behavior you DON'T want. Your hand is getting knocked back due to the increase in drag. It seems to me you want to minimize drag on the entry part of the stroke--you want your hand to slice through the water. Now, during the propulsive phase (the 'catch' I guess) maybe the technique you're suggesting is good because you want to maximize the surface area with which you're pushing against the water. I think it's a delicate balance, though. You are definitely increasing drag, but you really have to. The tricky thing is to produce as much force against the water as possible without increasing drag too much. It ain't easy!-

I can't think of a more complex problem to look at then the motion of the hand and arm in swimming. The complexity makes it all very difficult. As an engineer I would try to isolate one aspect from another in order to study it. But in this case doing so overlook sbig problems. Purely contrained to the propulsion aspect, I think many of the issues came out of an improper understanding of how the hands move both relative to the body and relative to the water. In particular in my experience, although your hands may move laterally to a great deal relative to your trunk, relative to the water the paths are much straighter due to trunk rotation. I think that sent us down a 10 year trip down the wrong road. The latest copy of Swimming Fastest has Coach Maglisco saying that drag forces create propulsion - sculling is dead. On the other hand we all know you can propel ourselves forward by sculling - log live the scull. I think we have lots more work to do in trying to understand swim propulsion. To be quite clear coach Maglischo recommends stright diagonal pulling motions that would involve an aspect of sculling. Now to throw the spaner in the works we can say, but what about biomecahnics? Just because in terms of fluid mechanics we can say a movement is optimal (not that we can right now) it is a big leap to say that we should make that move or make that move thousands of times a day. A good example someone else referenced is the thumb first entry recommended by Doc Counsilman. The fuid mechanics of it are solid - less reistsance. The biomechanics of it are solid in one aspect - gets hand i ngood postition for pull. But in another aspect it is biomechanically improper - exposure to injury. So in this case we have gone away from a technically solid technique purely because it exposes us to injury. The topic of swim propulsion is wide open I believe, we have seen some aspects that don't apply eg Bernoulli's law but others that quite probably do Newtonian fluid flow and some that just might, quasi steady state motion.