Announcer: GENTLEMEN,
START YOUR ENGINES!
Crew Member: GREEN, GREEN,
GREEN, GREEN...
Griff Jones:
THESE DRIVERS LOST CONTROL
AT VERY HIGH SPEEDS.
THE RESULT WAS TRAGIC
FOR ONE DRIVER...
AND FORTUNATE FOR THE OTHERS.
BUT WHY?
WHAT MADE THE DIFFERENCE
BETWEEN WALKING AWAY
AND BEING CARRIED AWAY?
THE ANSWER CAN BE FOUND
IN SOME OF THE MOST BASIC LAWS
OF THE PHYSICAL UNIVERSE.
HI, MY NAME IS GRIFF JONES.
I TEACH HIGH SCHOOL PHYSICS.
AND BEHIND ME IS THE INSURANCE
INSTITUTE FOR HIGHWAY SAFETY'S
VEHICLE RESEARCH CENTER.
IT'S A FASCINATING PLACE
WHERE RESEARCH ENGINEERS
ASSESS THE CRASH PERFORMANCE
OF VEHICLES BY RUNNING TESTS.
AND WHERE THEY EVALUATE
NEW TECHNOLOGIES
TO PREVENT INJURIES,
LIKE THIS STATE-OF-THE-ART
HEAD PROTECTION SYSTEM.
WHAT'S EXCITING FOR ME
IS THAT THIS IS A LABORATORY
OF PRACTICAL APPLICATIONS
IN THE SUBJECT I TEACH.
AND BECAUSE THEY'RE SET UP HERE
TO CRASH CARS
AND ANALYZE THOSE CRASHES,
THIS RESEARCH CENTER PROVIDES
THE PERFECT VENUE
FOR ILLUSTRATING
THE PHYSICAL LAWS
THAT GOVERN THE OUTCOME
OF CAR CRASHES.
SO FOLLOW ME,
AND FOR THE NEXT FEW MINUTES
I'LL TAKE YOU BEHIND THE SCENES
WHERE WE CAN EXPLORE
THE BASIC SCIENCE
BEHIND VEHICLE CRASHES.
LET'S LEARN ABOUT CAR CRASHES
AND PHYSICS.
WHY'D THIS DUMMY
GET LEFT BEHIND?
IT'S CALLED INERTIA,
THE PROPERTY OF MATTER
THAT CAUSES IT
TO RESIST ANY CHANGE
IN ITS STATE OF MOTION.
GALILEO INTRODUCED THE CONCEPT
IN THE LATE 1500s,
AND ALMOST 100 YEARS LATER,
NEWTON USED THIS IDEA
TO FORMULATE HIS FIRST LAW
OF MOTION, THE LAW OF INERTIA.
IT'S WHY THE DUMMY FELL
OFF THE BACK OF THE TRUCK.
IT WAS AT REST AND IT WANTED
TO REMAIN AT REST.
THAT'S INERTIA.
IT'S THE SAME PROPERTY THAT
KEEPS THE CHINA ON THE TABLE
AS YOU PULL THE TABLECLOTH
OUT FROM UNDER IT.
NOW WHAT ABOUT A BODY IN MOTION?
AM I A BODY IN MOTION?
YOU BET I AM.
I'M MOVING 35 MILES PER HOUR.
BUT FROM ONE PERSPECTIVE
IT MAY NOT LOOK LIKE
I'M MOVING AT ALL
BECAUSE IN RELATIONSHIP
TO THE PASSENGER COMPARTMENT,
MY POSITION ISN'T CHANGING.
BUT IF YOU LOOK AT ME
FROM THE OUTSIDE,
YOU CAN SEE THAT I'M MOVING AT
THE SAME SPEED AS THE VEHICLE--
IN THIS CASE,
ABOUT 35 MILES PER HOUR.
AND IF NEWTON WAS RIGHT,
AND WE KNOW HE WAS,
I'M GOING TO KEEP ON MOVING
AT THIS SAME SPEED
UNTIL AN EXTERNAL FORCE
ACTS ON ME.
NOW WHAT DOES THIS MEAN TO
OCCUPANTS OF A MOVING VEHICLE?
WATCH THIS.
SEE HOW THE CAR AND
THE CRASH TEST DUMMY
ARE TRAVELING AT THE SAME SPEED?
NOW WATCH WHAT HAPPENS
WHEN THE CAR CRASHES
INTO THE BARRIER.
THE FRONT END OF THE CAR IS
CRUSHING AND ABSORBING ENERGY,
WHICH SLOWS DOWN
THE REST OF THE CAR.
BUT THE DUMMY INSIDE KEEPS ON
MOVING AT ITS ORIGINAL SPEED
UNTIL IT STRIKES
THE STEERING WHEEL
AND WINDSHIELD.
THIS IS BECAUSE THE DUMMY
IS A BODY IN MOTION
TRAVELING AT 35 MILES PER HOUR
AND REMAINS TRAVELING
35 MILES PER HOUR
IN THE SAME DIRECTION
UNTIL ACTED UPON
BY AN OUTSIDE FORCE.
IN THIS CASE, IT'S THE IMPACT
OF THE STEERING WHEEL
AND WINDSHIELD
THAT APPLIES THE FORCE THAT
OVERCOMES THE DUMMY'S INERTIA.
INERTIA IS ONE REASON THAT
SEATBELTS ARE SO IMPORTANT.
INERTIA IS ONE REASON THAT YOU
WANT TO BE TIED TO THE VEHICLE
DURING A CRASH.
IF YOU'RE WEARING YOUR SEATBELT,
YOU SLOW DOWN WITH
THE OCCUPANT COMPARTMENT
AS THE VEHICLE'S FRONT END
DOES ITS JOB
OF CRUMPLING
AND ABSORBING CRASH FORCES.
LATER WE'LL TALK ABOUT
HOW SOME VEHICLES' FRONT ENDS,
OR CRUMPLE ZONES,
DO A BETTER JOB OF ABSORBING
CRASH FORCES THAN OTHERS.
BUT FOR NOW, LET'S GET
BACK TO NEWTON.
HE EXPLAINED THE RELATIONSHIP
BETWEEN CRASH FORCES AND INERTIA
IN HIS SECOND LAW,
AND THE WAY IT'S OFTEN
EXPRESSED IS F=ma.
THE FORCE "F" IS WHAT'S NEEDED
TO MOVE THE MASS "m"
WITH THE ACCELERATION "a."
NEWTON WROTE IT THIS WAY.
IT'S THE SAME THING.
ACCELERATION IS THE RATE
AT WHICH THE VELOCITY CHANGES.
BUT IF I MULTIPLY EACH SIDE
OF THE EQUATION BY "t,"
I GET FORCE TIMES TIME
EQUALS MASS TIMES
THE CHANGE IN VELOCITY.
WHEN NEWTON DESCRIBED
THE RELATIONSHIP
BETWEEN FORCE AND INERTIA,
HE ACTUALLY SPOKE IN TERMS
OF CHANGING MOMENTUM
WITH AN IMPULSE.
WHAT DO THESE TERMS MEAN?
MOMENTUM IS INERTIA IN MOTION.
NEWTON DEFINED IT
AS THE QUANTITY OF MOTION.
IT'S THE PRODUCT OF
AN OBJECT'S MASS, ITS INERTIA,
AND ITS VELOCITY, OR SPEED.
WHICH HAS MORE MOMENTUM:
AN 80,000-POUND BIG RIG
TRAVELING TWO MILES PER HOUR
OR A 4,000-POUND SUV
TRAVELING 40 MILES PER HOUR?
THE ANSWER IS, THEY BOTH HAVE
THE SAME MOMENTUM.
HERE'S THE FORMULA:
"p" IS FOR MOMENTUM--
I DON'T KNOW WHY THEY USE "p,"
THEY JUST DO--
EQUALS "m" IS FOR MASS, AND "v"
IS FOR VELOCITY...
p=mv.
THAT'S MOMENTUM.
AND WHAT IS IT THAT CHANGES
AN OBJECT'S MOMENTUM?
IT'S CALLED AN IMPULSE.
IT'S THE PRODUCT OF FORCE
AND THE TIME DURING WHICH
THE FORCE ACTS.
IMPULSE EQUALS FORCE TIMES TIME.
HERE'S MY FAVORITE DEMONSTRATION
OF IMPULSE.
I HAVE TWO EGGS, SAME MASS.
I'M GOING TO TRY AND THROW EACH
EGG WITH THE SAME VELOCITY.
THAT MEANS THEY HAVE
THE SAME MOMENTUM.
IF THE IMPULSES WERE EQUAL,
WHY DO WE HAVE SUCH
DRAMATICALLY DIFFERENT RESULTS?
THE WALL APPLIES
A BIG STOPPING FORCE
OVER A SHORT TIME.
THE SHEET APPLIES
A SMALLER STOPPING FORCE
OVER A LONGER TIME PERIOD.
MY STUDENTS SAY THE SHEET
HAS MORE GIVE TO IT.
BOTH STOP THE EGG,
BOTH DECELERATE
THE EGG'S MOMENTUM TO ZERO,
BUT IT TAKES A SMALLER FORCE
TO REDUCE THE EGG'S MOMENTUM
OVER A LONGER TIME.
IN FACT, SO MUCH SMALLER
THAT IT DOESN'T EVEN CRACK
THE EGG'S SHELL.
NOW LET'S RELATE THIS
TO AUTOMOBILES.
BOTH OF THESE CARS
HAVE THE SAME MASS
AND BOTH ARE TRAVELING
AT THE SAME SPEED,
30 MILES PER HOUR.
LIKE THE EGGS,
THEY HAVE EQUAL MOMENTA.
AS A RESULT, IT WILL TAKE
EQUAL IMPULSES
TO REDUCE THEIR MOMENTA TO ZERO.
ONE CAR WILL STOP
BY PANIC BRAKING
AND THE OTHER
BY NORMAL BREAKING.
IF BOTH DRIVERS ARE BELTED
SO THEY DECELERATE
WITH THEIR VEHICLES,
THE DRIVER OF THE CAR
ON THE BOTTOM
WILL EXPERIENCE MORE FORCE
THAN THE DRIVER ON TOP.
THIS IS BECAUSE IF THE IMPULSES
MUST BE EQUAL
TO DECELERATE
EACH CAR'S MOMENTUM TO ZERO,
THE DRIVER THAT STOPS
IN LESS TIME OR DISTANCE
MUST EXPERIENCE A LARGER FORCE
AND A HIGHER DECELERATION.
A "g" IS A STANDARD UNIT
OF ACCELERATION OR DECELERATION.
PEOPLE OFTEN REFER TO g's
AS FORCES, BUT THEY'RE NOT.
FIGHTER PILOTS CAN FEEL
AS MANY AS 9 g's
WHEN ACCELERATING
DURING EXTREME MANEUVERS.
AND ASTRONAUTS HAVE FELT
AS MANY AS 11.
PEOPLE IN SERIOUS CAR CRASHES
EXPERIENCE EVEN HIGHER g's,
AND THIS CAN CAUSE INJURY.
NOW CONSIDER WHAT HAPPENS
WHEN A CAR TRAVELING
30 MILES PER HOUR
HITS A RIGID WALL,
WHICH SHORTENS THE STOPPING TIME
OR DISTANCE
MUCH MORE THAN PANIC BRAKING.
LET'S AGAIN ASSUME
THE DRIVER IS BELTED
AND DECELERATES
WITH THE PASSENGER COMPARTMENT.
AND LET'S ALSO ASSUME THE CAR'S
FRONT END CRUSHES ONE FOOT
WITH UNIFORM DECELERATION
OF THE PASSENGER COMPARTMENT
THROUGHOUT THE CRASH.
IN THIS CRASH, THE DRIVER
WOULD EXPERIENCE 30 g's.
HOWEVER, IF THE VEHICLE'S
FRONT END WAS LESS STIFF,
SO IT CRUSHED TWO FEET
INSTEAD OF ONE,
THE DECELERATION WOULD BE CUT
IN HALF TO 15 g's.
THIS IS BECAUSE
THE CRUSH DISTANCE,
OR THE TIME THE FORCE IS ACTING
ON THE DRIVER, IS DOUBLED.
EXTENDING THE TIME OF IMPACT IS
THE BASIS FOR MANY OF THE IDEAS
ABOUT KEEPING PEOPLE SAFE
IN CRASHES.
IT'S THE REASON FOR AIRBAGS
AND CRUMPLE ZONES
IN THE VEHICLES YOU DRIVE.
IT'S THE REASON
FOR CRASH CUSHIONS
AND BREAKAWAY UTILITY POLES
ON A HIGHWAY.
AND IT'S THE ANSWER
TO THE QUESTION I POSED
AT THE BEGINNING OF THIS FILM.
THIS DRIVER SURVIVED THE CRASH
BECAUSE HIS DECELERATION
FROM HIGH SPEED
TOOK PLACE OVER
A NUMBER OF SECONDS.
THIS DRIVER DECELERATED
A SMALL FRACTION OF A SECOND
AND EXPERIENCED FORCES
THAT ARE OFTEN UNSURVIVABLE.
UP TO NOW, WE'VE BEEN LOOKING
AT SINGLE VEHICLE CRASHES.
BUT IF WE LOOK AT
TWO OR MORE OBJECTS COLLIDING,
WE HAVE TO USE ANOTHER ONE
OF NEWTON'S LAWS
TO EXPLAIN THE RESULT.
EVEN THOUGH THE FIRST CARS
WOULDN'T APPEAR ON THE ROADS
FOR OVER 200 YEARS,
COLLISIONS WERE AN ACTIVE TOPIC
OF PHYSICS RESEARCH
IN NEWTON'S DAY.
BACK IN 1662,
NEWTON AND HIS BUDDIES
FORMED ONE OF THE FIRST
INTERNATIONAL SCIENCE CLUBS.
THEY CALL IT THE ROYAL SOCIETY
OF LONDON
FOR IMPROVING NATURAL KNOWLEDGE.
ONE OF THE FIRST EXPERIMENTS
THEY DID
WAS TO TEST NEWTON'S THEORIES
ON COLLISIONS
USING A DEVICE LIKE THIS.
WHAT DO YOU THINK'S
GOING TO HAPPEN
WHEN I RELEASE THIS BALL AND IT
COLLIDES WITH THE OTHERS?
LET'S TRY TWO.
IT'S AS IF SOMETHING
ABOUT THE COLLISION
IS REMEMBERED OR SAVED.
NEWTON THEORIZED THAT
THE TOTAL QUANTITY OF MOTION,
WHICH HE CALLED MOMENTUM,
DOESN'T CHANGE.
IT'S CONSERVED.
THIS BECAME KNOWN AS THE LAW
OF CONSERVATION OF MOMENTUM
AND IT'S ONE OF THE CORNERSTONE
PRINCIPLES OF MODERN PHYSICS.
BEFORE WE APPLY THIS
TO CRASHING CARS,
WE NEED TO KNOW SOMETHING ELSE
ABOUT MOMENTUM.
IT HAS A DIRECTIONAL PROPERTY,
SO WE CALL MOMENTUM
A VECTOR QUANTITY.
THIS MEANS IF IDENTICAL CARS
TRAVELING 30 MILES PER HOUR
COLLIDE HEAD-ON,
THEIR MOMENTA CANCEL EACH OTHER.
INSIDE THE PASSENGER COMPARTMENT
OF EACH CAR,
THE OCCUPANTS WOULD EXPERIENCE
THE SAME DECELERATIONS
FROM 30 MILES PER HOUR TO ZERO.
THE DYNAMICS OF THIS CRASH
WOULD BE THE SAME
AS A SINGLE VEHICLE CRASH
INTO A RIGID BARRIER.
WHAT CONSERVATION OF MOMENTUM
TELLS US
ABOUT COLLISIONS OF VEHICLES
OF DIFFERENT MASSES
HAS IMPORTANT IMPLICATIONS
FOR THE OCCUPANTS
OF BOTH THE HEAVIER
AND LIGHTER VEHICLE.
IN A COLLISION OF TWO CARS
OF UNEQUAL MASS,
THE MORE MASSIVE CAR WOULD DRIVE
THE PASSENGER COMPARTMENT
OF THE LESS MASSIVE CAR
BACKWARD DURING THE CRASH
CAUSING A GREATER SPEED CHANGE
IN THE LIGHTER CAR
THAN THE HEAVIER CAR.
THESE DIFFERENT SPEED CHANGES
OCCUR DURING THE SAME TIME,
SO THE OCCUPANTS
OF THE LIGHTER CAR
WOULD EXPERIENCE
MUCH HIGHER ACCELERATIONS,
HENCE MUCH HIGHER FORCES THAN
THE OCCUPANT OF THE HEAVIER CAR.
THIS IS ONE REASON
WHY LIGHTER, SMALLER CARS
OFFER LESS PROTECTION
TO THE OCCUPANTS
THAN LARGER, HEAVIER CARS.
THERE'S A DIFFERENCE BETWEEN
WEIGHT AND SIZE ADVANTAGE
IN CAR CRASHES.
SIZE HELPS YOU
IN ALL KINDS OF CRASHES.
WEIGHT IS PRIMARILY AN ADVANTAGE
IN A CRASH WITH ANOTHER VEHICLE.
NEWTON WAS
A PRETTY BRILLIANT GUY.
THE LAWS OF MOTION HE ADVANCED
OVER 300 YEARS AGO
ARE STILL USED TODAY
TO EXPLAIN THE DYNAMICS
OF MODERN-DAY EVENTS
LIKE CAR CRASHES.
BUT EVEN NEWTON FAILED
TO RECOGNIZE
THE EXISTENCE OF ENERGY.
EVEN THOUGH IT'S ALL AROUND US,
ENERGY IS TOUGH
TO CONCEPTUALIZE.
SCIENTISTS HAVE HAD DIFFICULTY
DEFINING ENERGY
BECAUSE IT EXISTS
IN SO MANY DIFFERENT FORMS.
IT'S USUALLY DEFINED
AS THE ABILITY TO DO WORK,
OR, AS ONE OF MY STUDENTS SAYS,
IT'S THE STUFF
THAT MAKES THINGS MOVE.
ENERGY COMES IN MANY FORMS.
THERE'S RADIANT, ELECTRICAL,
CHEMICAL, THERMAL,
AND NUCLEAR ENERGY.
IN RELATING THE CONCEPT OF
ENERGY TO CAR CRASHES, THOUGH,
WE'RE MOSTLY CONCERN
WITH MOTION-RELATED ENERGY...
KINETIC ENERGY.
MOVING OBJECTS
HAVE KINETIC ENERGY.
A BASEBALL THROWN
TO A BATTER...
A DIVER HEADING
TOWARD THE WATER...
AN AIRPLANE FLYING
THROUGH THE SKY...
A CAR TRAVELING DOWN THE HIGHWAY
ALL HAVE KINETIC ENERGY.
BUT ENERGY DOESN'T HAVE TO
INVOLVE MOTION.
AN OBJECT CAN HAVE STORED ENERGY
DUE TO ITS POSITION
OR ITS CONDITION.
THIS IS A DEVICE
THAT DELIVERS A FORCE
TO A CRASH DUMMY'S CHEST
TO TEST THE STIFFNESS
OF THE RIBS.
THE FORCE IS A RESULT
OF THE KINETIC ENERGY
BEING TRANSFERRED
FROM THE PENDULUM
TO THE DUMMY'S CHEST.
AS THE PENDULUM SITS
AT ITS READY POSITION,
ITS POTENTIAL ENERGY IS EQUAL
TO ITS KINETIC ENERGY AT IMPACT.
WHEN IT IS RELEASED,
AND BEGINS TRAVELING
TOWARDS THE DUMMY'S CHEST,
THE POTENTIAL ENERGY TRANSFORMS
INTO KINETIC ENERGY.
IF WE FREEZE
THE PENDULUM HALFWAY,
WHAT IS ITS POTENTIAL
VERSUS KINETIC ENERGY?
THEY'RE EQUAL.
WHEN HAS THE PENDULUM REACHED
ITS MAXIMUM KINETIC ENERGY?
HERE, AT THE BOTTOM
OF ITS SWING.
THE AMOUNT OF KINETIC ENERGY
AN OBJECT HAS
DEPENDS UPON ITS MASS
AND VELOCITY--
THE GREATER THE MASS,
THE GREATER THE KINETIC ENERGY--
THE GREATER THE VELOCITY,
THE GREATER THE KINETIC ENERGY.
THE FORMULA THAT WE USE TO
CALCULATE THE KINETIC ENERGY
LOOKS LIKE THIS:
"KE," THAT'S KINETIC ENERGY,
EQUALS 1/2 mv-SQUARED.
THAT'S THE VELOCITY
MULTIPLIED BY ITSELF.
AND IF YOU DO THE MATH,
YOU'LL SEE WHY SPEED
IS SUCH A CRITICAL FACTOR
IN THE OUTCOME
OF A CAR COLLISION.
THE KINETIC ENERGY
IS PROPORTIONAL
TO THE SQUARE OF THE SPEED.
SO IF WE DOUBLE THE SPEED,
WE QUADRUPLE THE AMOUNT
OF ENERGY IN A CAR COLLISION.
AND ENERGY IS THE STUFF
THAT HAS POTENTIAL TO DO DAMAGE.
THE CONNECTION BETWEEN
KINETIC ENERGY AND FORCE
IS THAT IN ORDER TO REDUCE
THE CAR'S KINETIC ENERGY,
A DECELERATING FORCE
MUST BE APPLIED OVER A DISTANCE.
THAT'S WORK.
TO SHED 4 TIMES AS MUCH
KINETIC ENERGY
REQUIRES EITHER
A DECELERATING FORCE
THAT'S 4 TIMES AS GREAT,
OR 4 TIMES
AS MUCH CRUSH DISTANCE,
OR A COMBINATION OF THE TWO.
THE RAPID TRANSFER
OF KINETIC ENERGY
IS THE CAUSE OF CRASH INJURIES.
SO MANAGING KINETIC ENERGY
IS WHAT KEEPING PEOPLE SAFE
IN CAR CRASHES IS ALL ABOUT.
BRIAN O'NEILL IS THE PRESIDENT
OF THE INSURANCE INSTITUTE
FOR HIGHWAY SAFETY.
Griff: THAT'S INCREDIBLE.
Brian O'Neill: ONE OF THE THINGS
WE DO, WE PUT GREASE PAINT...
Griff: HE RUNS
THE VEHICLE RESEARCH CENTER
AND IS ONE OF THE FOREMOST
EXPERTS IN THE WORLD
ON VEHICLE SAFETY.
Brian: WE USE THE TERM
"CRASHWORTHINESS"
TO DESCRIBE THE PROTECTION
A CAR OFFERS ITS OCCUPANTS
DURING A CRASH.
NOW CRASHWORTHINESS
IS A COMPLICATED CONCEPT
BECAUSE IT INVOLVES MANY ASPECTS
OF VEHICLE DESIGN.
THE STRUCTURE,
THE RESTRAINT SYSTEM,
IT ALL ADDS UP TO THIS SINGLE
TERM WE USE, CRASHWORTHINESS.
WE USE THE STRIPPED-DOWN BODY
TO ILLUSTRATE THE CONCEPTS OF
GOOD AND POOR STRUCTURAL DESIGNS
FOR MODERN CRASHWORTHINESS.
Griff:
BRIAN, WHY IS IT IMPORTANT
FOR THE VEHICLE'S STRUCTURE
TO PERFORM WELL IN A CRASH?
Brian: WELL, THIS
IS WHAT'S LEFT
OF THE BODY AND STRUCTURE
OF A CAR THAT WAS IN A CRASH,
AND WE USE THIS
TO ILLUSTRATE THE POINT.
BASICALLY WE WANT
THE OCCUPANT COMPARTMENT,
OR THE SAFETY CAGE,
TO REMAIN INTACT.
WE DON'T WANT ANY DAMAGE
OR INTRUSION
INTO THIS PART OF THE VEHICLE
DURING THE CRASH.
WE WANT ALL OF THE DAMAGE
OF THE CRASH
CONFINED TO THE FRONT END.
Griff: SO EVEN THOUGH
ALL THIS METAL LOOKS THE SAME,
IT'S ACTUALLY DIFFERENT.
THIS, THE GREEN METAL'S
INTENDED TO CRUMPLE,
TO GIVE IN THE COLLISION.
Brian: IF WE CAN CRUMPLE
THE FRONT END OF THE CAR
WITHOUT ALLOWING ANY DAMAGE
TO THE OCCUPANT COMPARTMENT,
THEN THE PEOPLE INSIDE
CAN BE PROTECTED
AGAINST SERIOUS INJURY.
BASICALLY WE WANT THE FRONT END
TO BE BUCKLING DURING THE CRASH
SO THAT THE OCCUPANT COMPARTMENT
IS SLOWED DOWN
OVER A GENTLER RATE.
Griff: RIGHT...KIND OF LIKE
JUMPING OFF OF A STEP
AND KEEPING YOUR KNEES STRAIGHT
AND LANDING ON THE FLOOR
VERSUS BENDING YOUR KNEES
WHEN YOU LAND.
Brian:
EXACTLY THE SAME CONCEPT.
SO THIS IS A VEHICLE
THAT DID WELL
BECAUSE THERE'S
VERY LITTLE INTRUSION
ANYWHERE IN
THE OCCUPANT COMPARTMENT.
THESE ELEMENTS HERE, EVEN THOUGH
THEY'RE STRONG ENOUGH
TO HOLD AN ENGINE
AND SUSPENSION,
ACTUALLY BUCKLED AND CRUSHED
JUST LIKE THEY'RE DESIGNED TO DO
SO THE DAMAGE IS CONFINED
TO THE FRONT END.
WE LOOK AT A VEHICLE LIKE THIS
AND THIS IS AN EXAMPLE
OF A VERY POOR SAFETY CAGE.
THIS VEHICLE WAS
IN A 40 MILES PER HOUR CRASH
AND AS YOU CAN SEE,
THE OCCUPANT COMPARTMENT
IS COLLAPSED.
IT'S BEEN DRIVEN BACKWARDS.
AS A RESULT, THE DRIVER'S SPACE
HAS BEEN GREATLY REDUCED,
SO SOMEONE SITTING
IN THIS VEHICLE
IS OBVIOUSLY
AT A HIGH RISK OF INJURY.
Griff: SO EVEN IF THE RESTRAINT
SYSTEMS DO FUNCTION PROPERLY--
THE AIRBAG, THE SEATBELTS--
THE PERSON IS STILL
IN GREAT DANGER.
Brian: THIS PERSON
IN THIS VEHICLE,
EVEN WITH A BELT SYSTEM
AND AIRBAG,
IS AT SIGNIFICANT RISK OF INJURY
BECAUSE THE COMPARTMENT
IS COLLAPSING.
Griff: SO IT'S ANALOGOUS
TO SHIPPING A BOX OF CHINA.
YOU CAN HAVE ALL THE BEST
PACKING IN THE WORLD
AROUND THE CHINA,
BUT IF THE BOX IS WEAK,
YOU'RE GOING TO BREAK THE CHINA.
Brian: WHEN THE SAFETY CAGE
COLLAPSES,
YOU'RE GOING TO HAVE INJURIES
TO THE OCCUPANTS.
SO THIS IS AN EXAMPLE
OF POOR CRASHWORTHINESS.
BUT THIS VEHICLE WAS
IN THE SAME CRASH...
40 MILES PER HOUR, OFFSET CRASH,
AND YOU CAN SEE
THAT NOW THE SAFETY CAGE
HAS REMAINED INTACT.
THERE'S VERY LITTLE
INTRUSION ANYWHERE.
THE DAMAGE IS CONFINED TO
THE CRUMPLE ZONE OF THE VEHICLE.
THIS IS THE WAY IT SHOULD BE.
A PERSON IN A CRASH LIKE THIS,
WEARING THEIR SEATBELT
AND PROTECTED BY THE AIRBAG,
COULD WALK AWAY FROM THE CRASH
WITH NO INJURY.
Griff: RIGHT.
IF I STAND OVER HERE, AND I JUST
LOOK TOWARDS THE REAR OF THE CAR
AND I IGNORE THE AIRBAG,
THIS DOESN'T EVEN LOOK
LIKE IT'S BEEN IN A CRASH.
Brian: THAT'S RIGHT.
THIS IS GOOD PERFORMANCE,
GOOD CRASHWORTHINESS.
Griff: IN OUR
SHIPPING BOX ANALOGY,
THIS IS AN EXAMPLE
OF A STRONG BOX.
Brian: THAT'S RIGHT.
THE PEOPLE IN THIS BOX
WILL BE PROTECTED.
Griff: BRIAN, OBVIOUSLY
THIS CAR PERFORMED WELL,
BUT WHAT'S IN THE FUTURE
FOR CRASHWORTHINESS?
Brian: THIS IS AN ILLUSTRATION
OF HOW GOOD WE CAN DO
WITH FRONTAL CRASHWORTHINESS.
BUT FRONTAL CRASHES
ARE ONLY PART OF THE PROBLEM.
WE OBVIOUSLY ALSO HAVE TO PAY
ATTENTION TO OTHER CRASH MODES,
AND ONE OF THE MOST IMPORTANT
IS THE SIDE-IMPACT CRASH.
NOW THIS WAS A VEHICLE THAT WAS
IN A SEVERE SIDE-IMPACT CRASH.
THIS VEHICLE WAS GOING
20 MILES PER HOUR
SIDEWAYS INTO A POLE,
AND AS YOU CAN SEE,
IN A SIDE CRASH
YOU DON'T HAVE
ALL THE CRUSH SPACE YOU HAVE
IN A FRONTAL CRASH.
WE JUST HAVE THE WIDTH
OF THE DOOR AND THE PADDING
AND, IN THIS CASE, WE HAVE
AN AIRBAG ON THE INSIDE,
WHICH CREATES EVEN MORE SPACE.
WE INFLATE THE AIRBAG
TO CREATE MORE CRUSH SPACE.
AND WE ALSO HAVE
AN INFLATABLE AIRBAG
TO PROVIDE HEAD PROTECTION
UP IN THIS REGION.
THIS DEPLOYS
FROM THIS ROOF AREA HERE.
SO THE PHYSICS ARE THE SAME,
THE ENGINEERING CHALLENGES
ARE GREATER.
Griff: I AM ALWAYS
LOOKING FOR WAYS
TO RELATE THE PHYSICS
THAT I TEACH
TO THE REAL WORLD
THAT MY STUDENTS EXPERIENCE,
AND NOTHING IS MORE RELEVANT
THAN TRAVELING IN AN AUTOMOBILE.
YOU PROBABLY DO IT EVERY DAY.
I HOPE THAT MAKES THE MESSAGE
OF THIS FILM IMPORTANT
TO EACH AND EVERY ONE OF YOU.
I'VE ALWAYS BELIEVED
THAT IF A PERSON TRULY
UNDERSTANDS THE LAWS OF PHYSICS,
THAT PERSON WOULD NEVER RIDE
IN A MOTOR VEHICLE UNBELTED,
AND NOW THAT YOU'VE HAD
A CHANCE TO LEARN
SOME OF THE FINER POINTS
OF THE PHYSICS OF CAR CRASHES,
I HOPE YOU AGREE.
I ALSO HOPE YOU'VE LEARNED
WHY SOME OF THE CHOICES YOU MAKE
ABOUT THE TYPE OF CAR YOU DRIVE,
AND THE KIND OF DRIVING YOU DO,
CAN MAKE A DIFFERENCE IN WHETHER
YOU SURVIVE ON THE HIGHWAY.
REMEMBER, EVEN THE BEST
PROTECTED RACE CAR DRIVERS
DON'T SURVIVE
VERY HIGH SPEED CRASHES.
THE BOTTOM LINE IS, THE DYNAMICS
OF A MOTOR VEHICLE CRASH--
WHAT HAPPENS
TO YOUR CAR AND YOU--
IS DETERMINED BY HARD SCIENCE.
YOU CAN'T ARGUE
WITH THE LAWS OF PHYSICS.
