[Paddlewise] Paddle efficiency

From: Michael Edelman <mje_at_spamcop.net>
Date: Fri, 18 May 2001 13:52:00 -0400
Nick writes:

> There is a difference between the force applied and the amount of 
> energy required to generate that force. Effort and force aren't 
> really the same thing. Any propulsion force will create an 
> acceleration in the direction of the force. (F=ma).

True. You're defining "propulsion force" as "that component of applied
force that goes in to producing forward propulsion", right?

> ...However, you may end up applying 
> more energy into creating the force than you receive out of it. 

Right. Some of your energy will go into just heating the water.

>...So 
> even though the force applied to the paddle exactly equals the force 
> applied to the boat,

Right, Newton's third law. 

>... you can not say that the energy applied to the 
> paddle is equal to the energy received by the boat.

Absolutely.

> Energy received by the boat is equal to the energy applied to the 
> paddle minus the energy received by the water. Efficiency is (Energy 
> to Kayak)/(Energy to Paddle) and not (Force to Kayak/Force to Paddle).

We agree completely. I think most of the disagreement was indeed due to
our not all agreeing on the meaning of the terms we were using.

-- mike
---------------------------------------------------------------
Michael Edelman   mje_at_spamcop.net
http://www.foldingkayaks.org (nomadics)
http://www.findascope.com (choosing a telescope)
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Received on Fri May 18 2001 - 10:52:27 PDT

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