Today, we outrun a dinosaur. The University of
Houston's College of Engineering presents this
series about the machines that make our
civilization run, and the people whose ingenuity
created them.
It's unlikely you'll really
ever to have to outrun a dinosaur; but suppose you
did. Could you? Questions like that are deadly
serious business for Neill Alexander at Leeds
University.
You see, there's a lot we don't know about joints
-- about ankles, wrists, and knees. Is springiness
part of their motion? Or are they just hinges that
go where our muscles put them?
Both Alexander and a local biologist work with the
Zoo. When an animal dies, the biologist gets it
first and flays off the fat. She studies the way
mammals use their fat. Then she sends the lean meat
and bone to Alexander. "We have a Jack Sprat
relationship," he murmurs quietly, as he cuts in
with hacksaw and scalpel.
Occasionally he lays his hands on a human limb. But
animal size presents a baffling array of questions.
To understand humans, he must bracket them. He
studies mice on the one side and hippos on the
other. That's where the question about fleeing a
dinosaur comes in. Naturally, his lab -- his
charnel house -- includes dinosaur bones.
But let's look at the question of springiness
first: Alexander prides himself on the simplicity
of his methods. The only hi-tech instrument in his
lab is a tension-testing machine. He uses it to
measure elasticity in tendons and ligaments. The
human foot, it seems, is really a big spring. It
returns 70 percent of the energy we put into it,
but only when we run. That's why we shift to a run
when we want to go more than 5 miles an hour.
Running is a series of falls. It's fall and jump,
fall and jump. Running means using gravity, and
gravity doesn't treat an elephant the same way it
treats a mouse. Horses are especially interesting.
A horse breaks from a walk into a trot to
capitalize on the spring of his ankles. But then he
shifts gears a second time. He breaks from a trot
into a gallop. Why?
Alexander found the answer in films of galloping
horses. A galloping horse flexes his back. The
tendons of the back form another huge spring. At 11
miles an hour, the horse begins using it to
conserve still more energy as he runs.
So what about that Tyrannosaurus rex who's chasing
you? His legs are three times longer than yours.
But he cannot leap. His bones can't take a fall.
You could almost surely get away from him. Next
time you have such a nightmare, you can rest
easier.
And we see that the question isn't frivolous after
all. Alexander tells us what any good experimental
scientist knows. The world is a strange and
wonderful place. If we mean to understand reality,
we must be willing to test it all the way -- to
absurdity.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
(Theme music)
