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The question as it appears in the 06/19 edition of Specs & Techs from GlobalSpec:
Dad and his identical twin sons visit a building in Washington, DC. Dad tries an experiment, having read in his guidebook about one room in the building. Billy stands near the center of the room with Bobby to one side. Dad is directly opposite Bobby, with Billy halfway between.
Dad quietly says, "Who wants chocolate?" which both love. Only one son comes running. Which one and why? Bonus points for identifying the building!
Note: This is a question of Physics, NOT Physiology or Psychology.
Thanks to STL Engineer who submitted the original question (which we revised a bit).
(Update: June 26, 9:35 AM EST) And the Answer is...
ANSWER: Bobby heard his dad whispering,
and Billy did not. Bobby came running to get his chocolate bar and Billy kept
looking for "something special" unaware that Dad had already demonstrated its
function.
The Dad has chosen to visit the U.S.
Capitol building. In the Capitol building there is a room called the National
Statuary Hall. In this room the ceiling and walls form a partial ellipsoid. This
creates an effect known as a Whispering Gallery. If you stand at a certain spot
on one side of the room, which happens to be the focus of the ellipses formed by
the ceiling and walls, like Bobby, you can hear someone whispering at the other
focal point on the other side of the room, where Dad was, even though those in
between (Billy) cannot. This is because sound from one focal point is reflected,
redirected, and focused on the other point due to the shape of the ellipses,
making a whisper from across the room as clear as if the person were standing
right next to you.
Whispering galleries also occur in certain
enclosed arches and other domed areas by standing along the wall at one foot and
whispering to someone on the opposite side. In this case the sound is conducted
rather than focused, like speaking into an old fashioned "speaking tube" as used
to be common on ships before electrical telephones and electronic radios
replaced it.
In the entrance foyer of the Union Station
building in St.
Louis there is such an arched ceiling and wall. I love to
show it to friends and family whenever we visit there. Everyone is always
astonished at how well you can hear a whisper from over 50 feet
away!
You can also set up your own "Whispering
Gallery" if you have two large, smooth surfaced parabolic dishes whose concave
surfaces face each other directly. You may then stand, or sit, depending on the
size and mounting positions of the dishes, at the focal point of one parabola,
speaking towards that dish. A friend positioned in front of the other dish, at
its focal point will be able to hear you far across open ground (or water),
provided ambient noise is low enough, while those in between will not hear a
thing.
For more info, see the Wikipedia entries
for "Whispering
Gallery" and "National Statuary Hall".
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