National Geographic: The Invisible World Page #4

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athlete's movements

Computer-created images combined

with a mass of numerical data

can pinpoint

where athletic technique

is hindering performance

So, what coaches in the past thought

they can see with eyes

we are finding out you can not do

You have to quantify.

With the advent of computers

we can provide the coaches

with much more objective

reliable information on how

the body moves

Dr. Ariel's computer analysis

of Olympic discus

thrower Mac Wilkins revealed

that useful energy which would

effect his throw

was being wasted on ground friction

Additional force was being spent

by not rigidly planting his forward

leg at the moment of the throw

Based on this analysis

Wilkins altered his

throwing technique

Several months later

in international competition

he threw the discus over 13 feet

farther than he ever had before

and set a new world record

In a remarkable laboratory at the

Massachusetts Institute of Technology

time and motion are

dramatically dissected

With the aid of a pulsating

strobe light

Dr. Harold Edgerton can freeze a flurry

of movement onto a single plate of film

Dr. Edgerton developed the strobe

light in 1931

Unable to see how electric

motors behaved

when they rotated at various speeds

he designed a light which

could flash so quickly

and brightly that motion seemed

to stop

Now we're going to do an experiment

here to take a picture of a

bullet-a very high-velocity bullet

as it cuts this playing card in two

The playing card will be attached

to this tape

The bullet will come out of the

gun at 2,800 feet per second

If we aim it correctly

it'll cut through the card

And we want to turn on a light

a very special strobe light

that lasts less

than a millionth of a second

in order to stop the bullet

effectively on film

and make a sharp, clear photograph

The sound of the bullet will trigger

the strobe light

which creates an image on film

A first shot will

test Dr. Edgerton's aim

Here we go

Now, the event as the strobe

light reveals it

Less than a millionth of a second

is permanently frozen in time

Another striking example of the

strobe's revealing power is

what Edgerton calls "making applesauce"

Perhaps the most dramatic of

Dr. Edgerton's visual techniques

combines the powerful strobe light

with a high-speed

motion-picture camera

There you go. All set?

Three, two, one, two

Stretching events thousands of times

reveals invisible detail

that can be seen and studied

in no other way

The explosion of a firecracker

now slowed down 1,200 times

Examine the "plop" of a milkdrop

and it becomes a magical vision of

hydrodynamic behavior

Unbounded by our human sense of time

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