A lethal lashing tongue; A speeding handrail
Q: How long is the veiled chameleon’s tongue? Stella,
Hamilton, Canada
A two-horned chameleon in Tanzania. Photo courtesy of Ales
Kocourek and Wikipedia
A: A veiled chameleon is a small animal
— about 5 inches (12.7-cm) long, not counting his tail — with a tongue
longer than he. The tongue can stretch to six times its rest length, and
is about 7.5 inches (19.0 cm) long.
He needs a long, fast tongue because he is neither. The slow-moving creature never chases his prey but
only edges
towards it. He rocks a bit to judge the distance, focuses his
independent swiveling eyes and unleashes his tongue to smite the insect from
afar — up to one and a half body lengths away. The sticky tip gloms on.
The tongue whips out faster than our eyes can follow, speeding at 26 body lengths per second, according to two Dutch biologists:
Jurriaan H. de Groot, at
Leiden University and project leader Johan L. van Leeuwen, at Wageningen University.
The tongue hits the prey in about 30 thousandths of a second — one tenth of an
eye blink.
An Indian chameleon shoots out his tongue, from G.A. Boulenger,
Fauna of British India and Wikipedia.
To move that fast, the chameleon stores energy in collagen, much
as praying mantis and mantis shrimp do. He trips the apparatus, releasing
his tongue like an arrow shot from a bow.
"When triggered, the concentric, overlapping sheaths of collagen
telescope outward, allowing the adhesive tongue tip to extend rapidly toward the
prey," explains National Geographic News.
Further Reading:
How
chameleons change color, and why, WonderQuest
Shrimp
spring into shattering action, WonderQuest
A hunting praying mantis, WonderQuest
Catapults give chameleon tongues super speed, National Geographic News.
Functional implications of super contracting muscles in the chameleon tongue
retractors, the journal of experimental biology, 2001.
Veiled chameleons, Smithsonian National Zoological Park
International Wildlife encyclopedia,
edited by Maurice Burton and Robert Burton
Q: On escalators, why does the handrail move faster than the
stairs, it defies logic? Dan, Southampton, England
How an escalator works. Drawing from City of Denver, American Society of
Mechanical Engineers and Kone Escalators, modified by author.
A: When I first read this question, I paused and tried to remember.
Yes, it did seem like my hand went faster than my feet the last time I rode an
escalator, but I wasn't sure.
So, one fine spring afternoon recently, I hopped in my red 4Runner, and headed
north to the nearest big shopping mall: Cottonwood. I rode six
escalators, all that Cottonwood had. Boarding each one, I clamped my elbow
to my side (like I was holding a newspaper there) and reached for the handrail
as I stepped on the moving stairs. My hand kept pace with the rest of my
body. It did not tug me forward (moving faster) or
push me backwards (moving slower). I concluded handrails do a good job of
keeping even with the stairs.
How the handrail works:
The escalator drive shaft (which drives the stairs) also drives the handrail
belts through a gear wheel and chain system. So the handrail system is
closely, but not directly, coupled to the stair-drive system. Therefore,
it's possible for a moving handrail not to keep exact pace with its
moving stairs, according to
Otis Elevator Company. However, all the escalators I rode that day had
well-synchronized handrails.
I checked with the American Society of Mechanical Engineers about escalator
handrail safety codes. "Though I cannot comment on a manufacturer's
particular design," Geraldine Burdeshaw emailed, the code "does require the
handrail to be substantially the same speed as the steps." I've included
the pertinent safety code below.
Trivia
- The longest single-span uninterrupted escalator in Europe is in the Moscow
Metro; it is 413-feet (126-m) long, and takes nearly 3
minutes to ride.
- In the Western Hemisphere, the longest is in the Washington DC metro: 230-feet (70-m) long.
- Jesse Reno patented the moving stairs in 1892 and, four years later,
created a 6-foot escalator 'ride' on Coney Island in New York City.
Further Reading:
Escalator information, Otis Elevator Company
Magic
stairways, University of Houston
The Way Things Work: An Illustrated Encyclopedia of Technology, C. van
Amerongen, 1967.
Readers' answers:
- A faster handrail is not really possible because, if you were holding onto a handrail that was moving faster, you would lean over
gripping the handrail until you relaxed your grip or fell off the step. You never hear stories of people falling off
escalators. Another reason is that the stairs and the railing belt are
running off of the same drive wheel so there is no way the handrail could be
faster.
Josh, Stow, Ohio, USA
- Escalator steps are driven by an electric motor. The steps drive is
connected to the handrail drive by a drive belt. Over time, that belt can get
a bit stretched out. Without maintenance, it will eventually
break. This is why all escalators come equipped with handrail sensors.
Ultimately, it's a maintenance issue.
LdySaphyre, Gainesville, Florida, USA
- The handrail on the escalator moves faster than the stairs to motivate the
user to walk up the escalator and not just ride. If everyone walked up, even
slowly, this would allow more people to use the escalator, and satisfy the
person behind you who wants to get up the escalator faster.
Nick, Maysville, Missouri, USA
From the ASME A17.1 Safety Code for Elevators and
Escalators (2004 edition):
6.1.3.4.1 Type Required. Each balustrade shall be provided with a handrail
moving in the same direction and at substantially the same speed as the steps.
In the case of curved escalators, this shall be substantially the same angular
velocity. The speed of the handrail shall not change when a retarding force of
450 N (100 lbf) is applied to the handrail opposite to the direction of travel.
A later observation:
April: Don't
know whether I sent you my observation that the handrail straps beside ALL
escalators, and moving sidewalks, at the JFK airport move faster than the
footing does. If you keep your feet and your hand in one place, by the time you
reach the other end of a typical escalator or moving sidewalk you are leaning
forward at an angle of 30 degrees or so.
Guy, Lyme Regis, Dorset, England
(Answered April 9, 2007, Updated June 20, 2007)
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