Endurance.Net Ridecamp Archives

Steven and Rise Estergreen wrote:
> Truman,
>
> You have made this system too simple. Try walking half a mile on level 
> ground at a comfortable pace. That shouldn't be much of an effort for 
> anyone fit enough to ride a horse 50 miles in a day. Next, try hopping 
> half a mile in the same time,  but jumping at least six inches high at 
> every hop. By your theory, the same amount of  energy was used. 
> Gravity hasn't changed, your mass hasn't changed.
But the work you do does. When you are walking you are not moving a mass
against the force field - you are but just a little maybe an inch. If
you hop 6 inches up you are doing m x g x height amount of work on each
hop. That is vastly different. You use more energy because you are doing
more work. m x g x h is also the potential energy of the system. By the
Work-Energy theorem the work done moving a object from state a to state
b is the difference of the kinetic energy from the two states.
> In a similar manner the rider, by moving "with" or "against" the 
> horse, can determine in a big way the forces necessary to propel the 
> horse/rider combination upward, forward, or laterally. When the 
> rider rises from sitting to standing in the saddle, the force to 
> acclerate the rider upward must come from the ground, through the 
> horse. When the rider returns to the seat, the horse must deliver the 
> force necessary to stop the rider's downward motion (again an upward 
> acceleration) from the ground to the rider. Since the goal is forward 
> motion, neither the standing or the sitting (or the other, downward, 
> acceleration when the rider begins to move from standing to sitting) 
> contributed anything, and both of the upward accelerations resulted in 
> wasted energy for the horse.
I don't know how big the acceleration imparted by a slow rider really
is. You could test it by outfitting the horse with an accelerometer at
it's center of mass along with one at the rider's center of mass and
compare them. If they are the same the net acceleration of the rider
reference to the horse is zero. The difference will be the additional
force experienced by the horse.

But I doubt seriously if that will ever be done. Even if it was I
suspect it will be small compared the 9.8 meters/sec^2 acceleration of
gravity.

--

"It is even harder for the average ape to believe that he has descended
from man." H.L. Mencken



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