By Patrick Clinton
Why can't we get syrup from trees other than maples? Is
oaken pancake syrup possible?
Nick Galbreath, Boston, Massachusetts
You can make syrup out of sap from some other trees,
such as the butternut and the box elder, a cousin of
the maple. There's even minor commercial production of birch syrup. But
for the most part, only the sugar maple has sweet-enough sap
to make its harvest worthwhile. You'd have to boil down 150
gallons of birch sap for a gallon of syrup; the ratio
is about 40 to one for maple sap.
Sweetness, however, is just part of the story. Most trees don't
"bleed" sap like maples do. (Even maples bleed significantly only in
late winter when they're preparing to emerge from dormancy.) Oaks have
a more evolved circulatory system. They transport fluids only in a
narrow ring under the bark, so they heal quickly when cut.
Even if you could collect a bucket of oak squeezins, you
might not want them center stage on your flapjacks. According to
U.S. Forest Service plant pathologist Phil Wargo, "Ring-porous trees like oaks
convert carbohydrates into brown grungy things." The grunge helps fight off
fungi, which are big killers of trees. Very useful for the
oak, of course, but no perk at the pancake house.
Earth's core is constantly losing heat, right? Should we be worried
about global cooling?
Karen Erlandson, Goleta, California
Actually, earth is far from becoming the third snowball from the
sun. The core got hot about 4.5 billion years ago, when
Earth collided with another planet-size body. The core temperature was 10,000
or 12,000 degrees Fahrenheit then, and it's dropped by only about
a thousand degrees since. At that rate, the core will be
toasty for tens of billions of years. Besides, it doesn't contribute
much to the total planetary energy picture: Scientists measure the heat
energy radiated at Earth's surface in milliwatts per square meter, and
a football-field-size parcel gives off about 200 wattsenough to power a
couple of light bulbs.
Earth's radioactive elements produce new heat all the time. But the
main reason the core has stayed hot, according to University of
California Berkeley geophysicist Raymond Jeanloz, is that rock is a terrific
insulator. "Even if you could instantly turn off the core heat,
we wouldn't know it for millions of years," he says. "We'd
have volcanoes and earthquakes for a long time to come." So
don't you worry.
How do boomerangs work?
Chris Mills, Seattle, Washington
Before I explain this, Chris, I
want you to meditate on one
of life's mysteries: If you watch the wheel of a bicycle
someone's riding, the spokes above the axle move away from you
faster than the spokes below the axle. Got it? Take your
The wings of a boomerang are like the spokes of a
wheel. You throw a 'rang vertically, like a knife, as opposed
to horizontally, like a Frisbee, and the wing on top always
has more airspeed than the one on the bottom. The wings
are airfoils, which means they create lift; the more airspeed, the
more lift. (Remember, the boomerang is soaring sideways, so it "lifts"
to the side, not up.) If you're still with me, the
top wing has more lift than the bottom wing, so lift
forces threaten to tip the boomerang over.
But it doesn't tip, because of gyroscopic precession, the same force
that makes tops wobble weirdly when you play with them. Precession
relocates forces that act on spinning bodies. In this case, it
takes the tipping force and moves it 90 degrees forward, so
it becomes a steering force. The boomerang turns and keeps turning
until it comes back. Simple and elegant. Kind of makes you
wish aborigines had designed Windows 95.
Send your questions for The Wild File to Outside, 400 Market St., Santa Fe, NM 87501, or submit them here.