[ MUSIC ]
>> HELLO,
MY NAME IS MEGAN MCARTHUR.
>> MY NAME IS SHANE KIMBROUGH.
WE ARE LIVING AND WORKING
ABOARD THE INTERNATIONAL
SPACE STATION,
ORBITING 250 MILES
ABOVE YOUR HEAD.
HERE ON STATION,
WE LIVE IN A MICROGRAVITY
ENVIRONMENT,
WHICH ALLOWS US TO
EXPERIMENT WITH WEIGHTLESSNESS
AND PUSH THE BOUNDARIES
OF SCIENCE.
>> TODAY, WE WILL DEMONSTRATE
MOMENT OF INERTIA
BY FIRST USING
A LARGE FLASHLIGHT,
THEN DEMONSTRATING IT
WITH THE HUMAN BODY.
ARE YOU READY?
LET'S GO CHECK IT OUT.
INERTIA IS THE TENDENCY
OF AN OBJECT TO RESIST CHANGE
IN ITS CURRENT STATE OF MOTION.
THAT MIGHT SOUND FAMILIAR,
SINCE NEWTON'S FIRST LAW
OF MOTION IS ALSO REFERRED TO
AS THE LAW OF INERTIA.
MOMENT OF INERTIA,
ON THE OTHER HAND,
DESCRIBES AN OBJECT'S
TENDENCY TO RESIST
ROTATIONAL ACCELERATION.
AN OBJECT'S MOMENT OF INERTIA
IS A PROPERTY THAT DEPENDS ON
HOW MASS IS DISTRIBUTED
AROUND ITS AXIS OF ROTATION.
THERE IS A RELATIONSHIP BETWEEN
AN OBJECT'S MASS DISTRIBUTION
AND HOW IT EASILY IT SPINS
OR RESISTS SPINNING.
IN GENERAL,
OBJECTS HAVE A LOWER MOMENT
OF INERTIA AND ARE EASIER
TO SPIN IF THE MASS IS CLOSER
TO THE AXIS OF ROTATION.
AS YOU CAN SEE,
THE FLASHLIGHT ROTATING
ABOUT ITS LONGER AXIS
IS SPINNING AT A FASTER RATE
THAN THE FLASHLIGHT ROTATING
ABOUT ITS SHORTER AXIS.
THIS IS BECAUSE ITS MASS
IS CLOSER TO THE AXIS
OF ROTATION.
THE SPINNING FLASHLIGHT
IN THIS POSITION
HAS A LOWER MOMENT OF INERTIA,
WHICH MEANS THERE IS
LESS RESISTANCE TO ROTATION.
WHEN THE FLASHLIGHT IS SPUN
ABOUT ITS SHORTER AXIS,
ITS MASS IS SPREAD FURTHER AWAY
FROM THE AXIS OF ROTATION.
IN THIS POSITION,
THE FLASHLIGHT HAS
A HIGHER MOMENT OF INERTIA.
NOW LETS SEE IF THIS APPLIES
TO HUMANS AS WELL.
>> NOTICE HOW FAST MEGAN
IS SPINNING IN RELATION
TO HER BODY'S POSITION.
WHEN HER ARMS ARE TUCKED IN
TIGHTLY NEXT TO HER BODY,
HER MOMENT OF INERTIA DECREASES,
WHICH CAUSES HER TO SPIN FASTER.
WHEN HER ARMS ARE EXTENDED OUT,
MORE MASS IS PULLED FURTHER AWAY
FROM THE AXIS OF ROTATION,
WHICH INCREASES HER MOMENT
OF INERTIA AND CAUSES HER
TO SPIN SLOWER.
THIS HAPPENS BECAUSE
REDISTRIBUTING OUR MASS
CHANGES OUR MOMENT OF INERTIA,
WHICH, IN TURN,
CHANGES HOW FAST WE SPIN.
THANKS FOR COMING ABOARD
AND WATCHING OUR
STEMONSTRATION TODAY.
TO EXPLORE MORE
ON MOMENT OF INERTIA,
CHECK OUT THE CLASSROOM
CONNECTION LESSON THAT
GOES ALONG WITH THIS VIDEO
AND DISCOVER MANY OTHER LESSONS
AND ACTIVITIES AT THE STEM
ON STATION WEBSITE.
SEE YOU NEXT TIME.