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Dizziness on Merry-go-round, Not Earth
Name: Carol
Status: educator
Grade: 9-12
Location: IL
Country: USA
Date: Summer 2011
Question:
Why do we feel dizzy when we ride on a merry go round that
goes pretty slowly, but we feel nothing while riding on the earth
that travels in a circle at about 1,000 miles an hour?
Replies:
Hi Carol,
As a pilot who flies aerobatics, I deal with motion sickness sometimes.
From my understanding, it has to do with a disconnect between what your
body is feeling and what your eyes are seeing. On a merry-go-round,
your inner ear (where our sense of balance comes
from) tells our brain that we are moving, by sensing an apparent force
tending to pull you away from the center of rotation. But if you are
looking at your other friends on the merry-go-round, they are not
moving relative to you and so your vision is not sensing relative
motion. These senses conflict and ultimately lead to a sense of
disorientation and other symptoms of motion sickness.
So it is understandable then why we do not get motion sickness just
standing on the earth, regardless of speed. We do not visually sense
any relative motion. Also, the pull of gravity on us is constant (by
the way, the apparent centrifugal force from the rotation of the earth
is also constant and in fact negligible compared to the acceleration of
gravity). Our inner ear then is only telling us that we're being pulled
by gravity as normal but not accelerating in any direction, which
agrees with our visual information. Hence our senses are all in
agreement and no motion sickness.
Regards,
John C Strong
Carol,
Dizziness is more from rate of rotation (revolutions per second) than
from speed (meters per second). On the earth, we rotate once per day.
On a moderate merry-go-round, five revolutions per minute is common.
Dr. Ken Mellendorf
Physics Instructor
Illinois Central College
On Earth your head and inner ear are in a state of balance between
gravity and inertia. The fluid in you inner ear rests at its usual
position so you do not feel any acceleration as you spin with the earth.
On a merry go round there is no force pulling your head sideways. The
fluids in you inner ear are pushed to the outside of the turn and you
know you are spinning, even with your eyes closed.
For the same reason if you are on a jet plane approaching the airport
with your eyes closed, you cannot feel the plane turning. The pilot
tips the wings so that the forces on your body are balanced and you
cannot detect the turn with any senses but your eyes,(assuming a good
pilot and smooth air).
Hope this helps.
R. W. "Bob" Avakian
Instructor
Arts and Sciences/CRC
Oklahoma State Univ. Inst. of Technology
Carol, the key factors you feel are angular velocity and acceleration
(centripetal force), not the tangential linear velocity that your
question includes. Angular velocity is how fast you rotate and acceleration relates to how much change in movement you feel.
Your angular velocity on even a slow merry go round (1 revolution per
minute) is still much, much higher than on the rotating earth (1
revolution per day). And, the acceleration you feel on a merry go round
(a radius of a few feet) is much higher than on earth (with a radius of
thousands of miles). The linear velocity you feel is relative -- if you
travel at the same speed as another object, it does not feel like you
are moving. Such is the case with you an the earth -- you both move
along at basically the same speed, and so you don't perceive the
motion.
Specifically, there are little canals in the ears that influence your
sense of balance, and respond to the rotation of your head -- and
rotating faster (which is not the same as moving linearly) affects that
balance.
Hope this helps,
Burr Zimmermann
I found a detailed explanation of this process from a reliable source. I am passing this along to you rather than recreating the same explanation. Go to
http://www.madsci.org/posts/archives/1999-10/939275753.Ns.r.html
for a detailed explanation.
Vince Calder
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Update: June 2012
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