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RE: 4ped vs. 2ped maneuverability (was Re: A fundimental conundrum...)



I said:

> It's not a biped thing but a vertical weight mass distribution
> thing.  Less area to move around the area of spin means easier
> spins.

 Nathan said:

>>The technical term for this is polar moment of inertia.

us animator types may not study the technical math or physics behind   
something, but we gotta understand the basics of WHY things move like   
they do.  I didn't know this was a special physics property so I feel   
pretty good about learning this term-thank you

>>Humans have low PMI.  Bipedal dinosaurs have very high PMI, due to the
>>long tails and necks - they are horizonal plan bipeds, quite different
>>in mass distribution from the vertical plan that humans use.

that's what I meant by saying that dinosaurs wouldn't work the same way   
as humans because of the teeter-totter/see-saw shape

>>I have been working on physically simulating the turning dynamics of
>>dinosaurs.  Their high PMI might actually be an advantage because
>>they can manipulate it dynamically by swinging their tails (like a
>>ballerina does pulling her arms in during a spin).

 I thought about this since an ice skater spinning with arms outstretched   
will increase spin-speed and/or duration of spin by bringing the arms   
suddenly in, but couldn't picture the movement with a broomstick held out   
to one side and a (for want of a better shape) guitar held out by the   
neck in the other.
But that's for a spin in place.

 For a turn over ground while moving, I had problems with the   
inflexibility of the tail that Tom was describing a while back.  If a   
gymnast has ribbon wands (which are flexible) she loses minimal momentum   
in a spin-turn.  But the dinosaur can only shift the angle that the tail   
sticks out at and counter-swing the head.  Very stiff in parts

I can see one throw the head, neck and tail up to decrease their   
horizontal mass, but the awkwardness of vision this would create seems   
detrimental to a chase being succesful, and the tail return would   
probably snap into the ground before returning to it's regular horizontal   
position-which would hurt.  (would be a great way to skid to a halt,   
however)

If it swung it's head in the direction it wanted to turn into, and   
snapped the tail over hard in the opposite direction, it would certainly   
help in a turn because otherwise a bipedal theropod would have to do BIG   
circles around to come back at something.

However, if chasing a quadrepedal dinosaur it would have a slight   
advantage in that the tail/head swinging might make it more flexible in a   
turn that it's prey so most of the chases would probably be a quadrepedal   
dinosaur simply trying to outrun the therapod with not much maneuvering   
by the chasee.
If chasing a bipedal dinosaur (other T rexes, Gallimimus, or whatever)   
the smaller dinosaur would have the maneuvering advantage and the bigger   
dinosaur would have the stride advantage.
And if chasing little ol' mammals and lizards, well, if it gets to cover,   
the littlest guys win.

>>I don't have full results yet so its hard to comment further.

oh, please....I think this sort of thing is great.  How do you propose   
the sauropods turn?  And would you say the hadrosaurs turn on 4 legs or   
2?

 -Betty