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Weightless at Earth’s center, long life, super speed
 Q: How much would I weigh at the center of the earth? (Naza,
Boise, Idaho
As you fall, there’s less Earth below you pulling down and
more above pulling you up. [Clip art from Corel Corporation]
A: Nothing.
A good way to see this is to imagine yourself falling through
Earth. Suppose there is a perfectly smooth well that goes straight through Earth
and out the other side. It’s airless so there is no air friction to hold you
back and forget about the huge temperatures and pressures down deep. This is a
thought experiment. You take an impossibly deep breath, step over the edge, and
fall into the well.
As you step off, all of Earth is below you and that entire
mass pulls your mass and you start to fall. As you fall, though, now some of
Earth is above you and there is, consequently, less Earth below you. The
farther you fall, the less of Earth there is below pulling you down and the more
Earth mass there is above pulling up. So you get lighter as you fall.
Finally, (about 21 minutes later) when you reach the center of
Earth, you weigh nothing at all because half of Earth is above you and half
below. The two pulls cancel.
By the way, you’re going your fastest now as you whiz towards
the opposite end of Earth at a blazing 17,700 mph (28440 km/h). In another 21
minutes you’ll pop out of the well somewhere in the middle of the Indian Ocean.
Then — back you go towards Kansas or where ever you started from.
"You’ll continue to bob back and forth through the center of
the Earth with your head popping out at your starting point every 84.5 minutes,"
says
Rod Nave, physics professor at Georgia State University. "It’s amusing that
this is about the same time it takes a satellite to orbit Earth (right above the
surface)."
Further Reading:
HyperPhysics by Rod Nave: Hole through Earth
HyperPhysics by Rod Nave: Earth’s gravity
Hewitt, Paul G. Conceptual Physics. New York:
Addison-Wesley, 1998.
Q: Regarding your answer for the longest-lived animal, I have
a correction: the rougheye rockfish (Sebastes aleutianus) has been aged
to 205 years. The age was determined by a validated method of counting the rings
on the fish's otolith
(which is similar to counting the rings of a tree). (Daniel, Durham, New
Hampshire).
A: My readers are among the most knowledgeable. Daniel’s
205-year old rougheye rockfish (Sebastes aleutianuns), found off the
coast of Alaska, trumps the 177-year old giant tortoise. In the tortoise’s
favor, though — she dwells in captivity. So, we know her age.
(Or do we? Charles Darwin captured Harriet, the tortoise, in
1835 when she was about 5 years old and took her to England. In 1841, the
Beagle brought Harriet to Australia and left her in a botanical garden.
Unfortunately, a 1920-flood destroyed all the garden’s animal records. So, we
don’t know exactly how old Harriet is.)
 Northern quahog, similar to the extremely
long-lived Ocean quahog. [NOAA]
The Ocean Quahog (Arctica islandica) — a clam — is
perhaps oldest of all. We recently dredged up a specimen, from the mid Atlantic
continental shelf, that had 220 annual growth rings. Biologists verified the
specimen’s age using radiometric- dating techniques. That creature’s 220 years
beats even the rockfish’s 205.
Further Reading:
WonderQuest: Longest and shortest life spans
Wikipedia encyclopedia: Harriet
Alaska Department of Fish and Game: Maximum ages of
groundfishes in waters off Alaska and British Columbia and considerations of age
determination by Kristen M. Munk
Conchologists of America: Growth rings and longevity in
bivalves by Dr. Douglas S. Jones
Q: How fast is warp speed? (Tom, Miami, Florida)
 Star
Trek’s Enterprise zips along at warp speeds. [Enterprise by Dennis Russell
Bailey, Earth by Fabio Passaro © 2004, used with permission]
A: Faster than light — science fiction, of course. In the real
world, any object with mass can’t go faster than light.
Star Trek’s Enterprise had no problem, though. Warp 1
was simply the speed of light. Tame stuff for the Enterprise. The
starship rarely traveled this slowly but she does have her limits.
The creator of the series, Gene Rodenberry, wanted a speed
limit so the Enterprise wouldn’t zip through the galaxy too fast for the
plots to keep up. So the tech advisor said fine: Warp 10 is the maximum —
originally set at 1000 times the speed of light. The speed of light (called c)
is 186,000 miles per second (300000 km/s).
Star Trek: The Next Generation later redefined Warp 10
http://www.ex-astris-scientia.org/treknology/warptable.gif to be
infinite so newer ships could travel faster than 1000 c. This puts
the modern fast ships somewhere between Warp 9 and Warp 10, says Bernd Schneider
of Ex Astris Scientia. For instance, Enterprise-D achieved Warp 9.6
(almost 2000 c) to escape an entity known as "Q."
Further Reading:
WonderQuest: Nothing passes light
Ex Astris Scientia, Bernd Schneider’s Star Trek site
Star
Fleet bulletin board: Warp speed defined
(Answered Dec. 17, 2004)
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