Gerald Foodman wrote: > I assume that most of the energy a paddler expends is to move the > boat forward. While changing sides, no paddler energy is moving the > boat forward. Hence, changing sides energy is small compared to the > power phase. and: > The idea that the potential energy stored while lifting the arms is > then returned to move the boat forward is false [...] > [The] power must come from the paddlers muscles, and only after the > blade is fully immersed. I made a little video with a mythbuster-like test, showing the validity of the principle: http://www.youtube.com/watch?v=TIm_d3eqzak I conclude that it IS possible to store potential energy in your arms and paddle, and use it to propel a kayak. --------------------------------------- I feel a need to summarize the discussion so far: We're talking about my youtube-video on the physics of the forward stroke: http://www.youtube.com/watch?v=-aB0rdn4UnQ Gerald Foodman wrote: > In the video you call the power phase of the stroke the resting phase. > This is incorrect and will mislead students. This was best answered by Carey: > I guess if you are the kayak, the arms moving down and back is the > "power" phase of the stroke, but if you are the arms, it would indeed > be the rest phase. So it becomes a perspective issue doesn't it? It > is both the power phase and the rest phase at the same time. Gerald Foodman wrote: > Plus, very little energy is required to change sides, which again > is contrary to what is said in the video. I made the calculation: Up to 30 watts is stored and released by just lifting and lowering the paddle. Since 30 watts is what's needed to propel a kayak at about 2 miles an hour, I consider the amount of energy significant. Gerald Foodman wrote: > Take two limiting cases. First the wing stroke: [...] the upper arm > staying at the same level [...] the wrist near the immersed blade > also stays at the same level. A random instruction video from youtube proves otherwise - as does my own video with my own stroke. I recalculated the energy of my own stroke, as seen in my own video. My hands and paddle, when resting on a scale,weigh about 7 kilos. During my stroke, I drop the paddle about 40 centimeters. I lift and drop an arm every second - which comes close to the 30 watts I claimed earlier. Gerald Foodman wrote: > Second case is a very low Greenland type stroke as taught, for > example, in Doug Van Doren's video. Again there is very little > altitude change of the arms during the power phase. The greenland stroke might be a completely different stroke - I don't know, I never studied it. It doesn't matter: I'm not talking about the greenland stroke. I think that covers all objections so far. I'm hoping for more solid arguments: I was really hoping for a serious discussion on mechanics. I still MIGHT be wrong, even very wrong; but so far, I have no indication that I am. Niels *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************Received on Thu Apr 28 2011 - 04:57:20 PDT
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