Nick, doesn't your (and John's) analysis of "equal and opposite reactions" assume that a kayak paddle works more like a rocket engine than like the wheels of a car? Rocket propulsion (based on Newtonian equal and opposite reactions) is not the only way to make a mass move forward; good old friction works well, too. Your automobile moves forward quite well even though the tires are not pushing little bits of pavement backwards. Instead, the friction of the wheels against an immovable surface converts nearly all the energy applied to the wheels to the forward movement of the car (maybe the car gets a little more Newtonian if driven in sand!). Rocket engines are much less efficient, since as much energy is imparting backwards momentum to particles of something as is going to moving your vehicle forward. I suspect that a kayak paddle works more like a hybrid between a car wheel (friction) and a rocket engine (Newtonian reactions). Friction is good for these purposes, and the more friction between the paddle and the water (ie, the less slippage) the greater proportion of your paddle stroke energy will go to moving your kayak forward even without an Newtonian reactions. Paddling a kayak in outer space, of course would be a different matter. Since there is no water or atmosphere then to work against with friction, only a rocket engine works there. --Karl Coplan *************************************************************************** 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/ ***************************************************************************
Actually a car works like a spaceship too. It is just pushing the whole earth. Since the earth has more mass than your average rocket fuel it is not accelerated much. As a result the kinetic energy added to the earth by driving your car is not going to show up on many seismographs. Momentum is still conserved. At 10:40 AM -0400 7/25/02, Coplan, Karl wrote: >Nick, doesn't your (and John's) analysis of "equal and opposite reactions" >assume that a kayak paddle works more like a rocket engine than like the >wheels of a car? Rocket propulsion (based on Newtonian equal and opposite >reactions) is not the only way to make a mass move forward; good old >friction works well, too. Your automobile moves forward quite well even >though the tires are not pushing little bits of pavement backwards. >Instead, the friction of the wheels against an immovable surface converts >nearly all the energy applied to the wheels to the forward movement of the >car (maybe the car gets a little more Newtonian if driven in sand!). Rocket >engines are much less efficient, since as much energy is imparting backwards >momentum to particles of something as is going to moving your vehicle >forward. > >I suspect that a kayak paddle works more like a hybrid between a car wheel >(friction) and a rocket engine (Newtonian reactions). Friction is good for >these purposes, and the more friction between the paddle and the water (ie, >the less slippage) the greater proportion of your paddle stroke energy will >go to moving your kayak forward even without an Newtonian reactions. > >Paddling a kayak in outer space, of course would be a different matter. >Since there is no water or atmosphere then to work against with friction, >only a rocket engine works there. > >--Karl Coplan -- Nick Schade Guillemot Kayaks 824 Thompson St Glastonbury, CT 06033 (860) 659-8847 *************************************************************************** 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/ ***************************************************************************
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