On Mon, 24 Jan 2005 23:26:39 +0100, "Sandy" <[email hidden]>
Quoted message said:<[email hidden]> a écrit dans le message de :
news:[email hidden]...
Quoted message said:Dear Sandy,
The calculation isn't really that hard. Newton's Second Law
of Motion:
Force = Mass x Acceleration
Just what I wanted. you do the work.
Quoted message said:The initial stomp on the pedal is probably what breaks the
crank (which is probably fatiguing), so the advantage of the
professional sprinter who can maintain impressive forces for
several seconds while isn't as big as you might think.
I can't quite figure out your syntax here, but that seem crucial. The
acceleration of a top athlete gottza be HUGE, and mr Colina may somehow
compensate with mass. Still doesn't get to my question : "do we look at the
design or the
manner or use, or what, to understand why a square taper axle is reliable
for one and not for the other."
Dear Sandy,
Try "while sprinting isn't"--the missing word enhances both
the meaning and the prosody.
No, the acceleration of a top athlete isn't necessarily huge
on a bicycle, whose gearing trades force for distance (the
reverse of a car jack).
Remember, bicycles differ from snails in that . . . Well,
there's probably some difference, but it isn't their
acceleration.
The top athletes (and their bicycles) at up to 100 kg
produce fantastic acceleration for a few seconds and then
taper off. So they put out a force of 1F.
A rider who weighs up to 200 kg (with his bike) and
accelerating at only half their rate requires the same force
of 1F.
Another way to look at it is to ask how much force you can
stomp onto a pedal while heaving as hard as you can on the
handlebars.
A small female rider at around 100 pounds has only 100
pounds of gravity assist and muscles used to moving only 100
pounds around.
A large male rider at 200 pounds has 100 pounds more of
gravity assist and muscles used to moving an extra 100
pounds around.
A huge rider at 400 pounds has 300 pounds more of gravity
assist and muslves used to moving the equivalent of four
small female riders or two large male riders.
You wouldn't want to have your finger trapped between the
pedal and the foot of any of these riders if they decided to
sprint, but the huge rider could put 400 pounds onto your
finger just by leaning his weight onto one foot.
The large male 200-pound rider would have to throw all his
weight onto your finger and then add another 200 pounds of
force by heaving on the handlebars.
The small female rider could produce only 100 pounds of
pressure on your finger by standing en pointe--she'd have to
pull down on the bars with 300 pounds of force to match the
huge rider's effect.
Big riders put more force into pedals, which is lucky, since
they need more force to accelerate at the same rate as
lighter riders.
As for the design, it's not just the spindles that
break--the pedal arms break, too. Most riders are under 200
pounds, so the problems of people who weigh twice as much
aren't likely to be addressed.
If all riders were women, the average weight and force would
be less, and we'd see bicycles with lighter, weaker
parts--and they'd hold up nicely.
Carl Fogel
