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?
Former Member
U of Wisconsin ran tests in the 50s, a cupped hand presses less water. A hand that was not cupped but the fingers touching, the thumb touching the pointer finger and an open hand with the fingers apart moved the same amount of water. I don't have the documentation but I was told this by a professor from there.
George Park www.swimdownhill.com
I also was taught to cup my hands when I swim. For myself, it feels like I am moving better thru the water with my hands slightly cupped. I had seen some swimmers in the trials with their fingers spread apart but not stretched apart, and it seemed to work for them. To each his own I guess.
The force you can generate with your hand will be dominated by form drag, basically the larger the cross-sectional area the more force you can generate. Cupping your hand to any extent will reduce the cross section and reduce the force. Holding your fingers together or apart doesn't change the area, just the shape. Having your fingers apart will increase the surface area of your hand increasing the surface drag, but the contribution of surface drag relative to form drag is probably not very significant. Learning to effectively use the entire forearm will increase the cross-sectional area a lot more significantly, using a high elbow position is the most important part of this. I don't actually like the term high elbow position because it refers to where your elbow should be if you are swimming flat, if you are on your side you want a wide elbow, the goal is a bent elbow so that your forearm is perpendicular to your direction of travel.
At least that's the theory as I understand it.
Actually, the mention of moving water brings up a topic I often wonder about: how much of the force is generated due to action/reaction/conservation-of-momentum and how much is due to viscosity effects? Swimming books often talk as though you can only accelerate forward by accelerating water backward when this clearly isn't the case, the viscosity of the water allows you to generate forces beyond simple mass momentum equations, but I don't know quantitatively what the relative contributions are. Anybody out there that is still up on their fluid dynamics?
Newton's second law states "The acceleration of an object is directly proportional to the net external force acting on the object and inversely proportional to the mass of the object," this law effects swimming in a large way. It is more easily understood as F=ma. "F" will be the force exerted by the swimmer, "m" will be the mass of the swimmer, and "a" will be the acceleration of the swimmer, using this equation you can find how much force a swimmer must exert to move through the water. Although it is not totally accurate because of the friction of the water it does explain the basic force a swimmer must exert. As you can see the swimmers mass and how fast he or she wants to go determine how much force must be exerted.
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!
Originally posted by LindsayNB
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.
As long as we are being picky :D the wheel may be rotating at a constant rate, but the blades are always accelerating. Any object moving in a curved motion has to be accelerated (otherwise it would be moving in a straight line).
Aaaaannndddd back to our regular subject... ;)
Found this article with a Google search:
Analysis of Swimming Techniques using Vortex Traces
...which is probably more than most people want to read. :eek: I think the passage that is most relevant is quoted next. The idea of pushing a handful of water backwards (like a jet) is somewhat misleading. Paddling may be easier to model and comprehend, but the evidence is that the 2nd method (involving a vortex) is more energy-efficient.
Principles of propulsion as known from the realm of aquatic animals are closely related to the way how the counter bearing is produced (Webb, 1988):
via use of pressure differences, e.g. paddling of Ducks;
via use of vortex - induced momentum in conjunction with acceleration reaction, e.g. whip lash like movement of 'profiled' flukes or fins of Dolphins, Sharks or true Seals;
via use of hydrodynamic lift, e.g. flying through the water of Mantas, Penguins. The difference in producing the counter bearing is related to the different morphological properties of the animals.
Originally posted by LindsayNB
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.
I have tried that experiment after wipeing the bottom of a model paddle wheel boat with camphorated oil, with the paddles removed, you woud be amazed how far it went with a push. Camphorated oil breaks down the tension.
George
Mattson,
Thank you for the link, i have printed it out and will study it later.
Linsday,
Now i see what you were saying. I was confused as i was looking at the force in ( F=ma ) as being only the propulsive force. Then taking that value and subtracting the Drag Forces to arrive at a Velocity.
I think that your maths ability is way ahead of mine !:)
Question, now that we have discussed this, can we now go out and break any records ?
A hand that was not cupped but the fingers touching, the thumb touching the pointer finger and an open hand with the fingers apart moved the same amount of water.
Almost the ok symbol with your hands?
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.
