OK this sounds like a stupid question but someone at the pool told me that my hand needs to be open with my fingers apart when I swim. i normally cup it which is what I thought was the best way. Today I tried my fingers together and my thumb out a little bit from the hand.
The cupped hand seemed best but what do the experts say?
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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.
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.
