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/ ***************************************************************************Received on Fri Jul 26 2002 - 06:26:51 PDT
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