Re: RC: Up Hill or Down

[Tivers@aol.com]

In a message dated 1/9/00 2:59:05 PM Pacific Standard Time, 
dleblanc@mindspring.com writes:

<< Actually, if you look at the static load on a horse standing on a hill
 (aligned with the slope), you'll find that the proportion of the load on
 the front is going to be a function of where the animal's center of gravity
 is located.  If the horse lowers the back-end, it will carry more weight on
 the rear legs. >

Pard, standing on the flat the horse bears 60% of its weight on the forelegs. 
You're telling me that going down hill at a trot is going to move the center 
of gravity rearward far enough that the hindlegs take the burden? Please show 
me a picture of this happening so I can send it to the Smithsonian. 

 >Also, if the horse brings the back legs up under itself,
 this also increases the loading on the rear legs.  Any time the load on
 something isn't perfectly distributed, the support loading is going to be a
 function of 2 things - the first is that the sum of the loads on the
 supports must be equal to the total load (else it falls or flies), and that
 the distance to the support from the center of gravity times the load on
 the support must equal out, or the object will spin about the center of
 gravity.  That's the picture from a statics engineering standpoint, and the
 statics of a horse going downhill with a rider on it is anything but simple>

You'ved greatly oversimplified it here--in the wrong direction, defying 
gravity and the laws of physics. 

 >(I wouldn't give this problem to students until they were through the first
 1/2 of a good statics course).  Now when you account for the fact that the
 whole thing is in motion, then we need to deal with dynamic loading, and
 given that a horse's skeletal structure isn't remotely simple, it would
 take me quite a while to cook up a numerical simulation that would give us
 any really solid answers.>

No need to delve deeply into the religions of math--accelerometer data is 
already available in the horse.
 
> Incidently, not really understanding the dynamics of a system is why we
 build bridges with a 'safety factor' of 10 - what it means is that we
 really don't understand how the bridge really works, so if we add a lot of
 extra steel and concrete, we hope it won't fall down. <g>>

The existentialist bridge builder. 
 
 >So anyway, what it boils down to is that Heidi's correct on this - the
 horse can make adjustments that will change the loading between front and
 back.  Since the way the horse carries itself does impact the loading
 between front and back (if you're OK at trig and algebra, this can be
 worked out), it is reasonable to assume that muscle stress must have
 corresponding differences.>

This will be very easy for you to demonstrate--just show me a picture of a 
horse galloping or trotting down hill with this radically shifted center of 
gravity. We can send it out on the next SETI mission to show just what is 
possible here on Earth.
 
> It's also true that if the horse tends to keep its back more level, the
 rider's weight won't ride quite as far forward, and that will affect the
 overall loading.>

All I need to see is a horse running "flat" down a hill. Then all your 
theorizing will be proven and I'll humbly accept defeat.
 
 
 >David LeBlanc
 dleblanc@mindspring.com
 
  >>

ti


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