Re: [Paddlewise] Legs Are Everything was "Long-short; euro-GP..."

 "Michael Daly" <mikedaly_at_magma.ca> wrote:

> On 7 Sep 2004 at 0:33, Dave Kruger wrote:

>> Caveat:  any backward-pushing force from your body to the boat negates
>> some of the forward-pushing force.  For example, if your lower back is
>> simultaneously pushing hard against the seatback (or backband), that
>> force drives the kayak rearward.

> This isn't quite true.  If you push your feet hard against the
> footpegs and your back against the backband, all you're doing is
> stretching the kayak (infinitesimally, but it can be measured with a
> strain guage).  It would be impossible to move the kayak backwards
> this way.  It does waste muscle energy and can contribute to fatigue
> if you keep it up.

Ah, I think we have a semantic difference here, Michael.  No quarrel with 
your analysis, except:

1. You can do work on the kayak by pressing on the foot pedals, because as 
you pump against them (during stroking), the force exerted times the distance 
the kayak (pedal) moves during that exertion _relative to the paddler_ would 
constitute work done by the paddler system on the kayak system.

2. Righto re:  stretching the kayak comment above.  I should have tightened 
that up and noted that it is the NET force your body exerts on the kayak that 
accelerates it:  meaning, any counterforce against the backband is countered 
(in turn) by some of the forward-directed force on pedals, hull, etc.  In 
short, the isometric extension your body accomplishes when pressing both 
surfaces will only make you more tired ... and does not accelerate the kayak. 
Only the NET force does that.

I think we are in agreement, just using different words.

--
Dave Kruger
Astoria, OR 
***************************************************************************
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/
***************************************************************************