On 10-Mar-2005, Kieran wrote:

Hmmm... this seems to be the part I'm missing. How do you get power
without knowing the path of the force?

Determining the moment in the shaft at some point allows you to resolve
the force at another point (say, centroid of area of the blade). Knowing
the paddle motion, from the video analysis you can do, will allow you
to determine the velocity of that centroid. Hence the power out. Since
power is a scalar, not a vector, you don't have to worry about direction.

However, that is total power in, not power that drives the kayak forward.
That is, if you calculate (estimate) the power to drive the kayak (total
hull resistance times hull velocity), it will be less than the power that
the paddle generates.

Mike

Michael Daly wrote:
On 10-Mar-2005, Kieran wrote:


Hmmm... this seems to be the part I'm missing. How do you get power
without knowing the path of the force?


Determining the moment in the shaft at some point allows you to resolve
the force at another point (say, centroid of area of the blade). Knowing
the paddle motion, from the video analysis you can do, will allow you
to determine the velocity of that centroid. Hence the power out. Since
power is a scalar, not a vector, you don't have to worry about direction.

Yes, all this I already knew... basically you're saying you DO need to
know the path of the force to get power. It seemed that Alan was
implying there was another way, just by knowing the force-time relationship.

However, that is total power in, not power that drives the kayak forward.
That is, if you calculate (estimate) the power to drive the kayak (total
hull resistance times hull velocity), it will be less than the power that
the paddle generates.

Actually, that's kind of the point. We want to know how much power the
paddler develops and puts into the paddle.

-Kieran