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CATEGORIES:Isaac Newton Institute Seminar Series
SUMMARY:An Introduction to the Mechanics of the Lasso - Ne
il Ribe (CNRS (Centre national de la recherche sci
entifique)\; Université Paris Saclay)
DTSTART;TZID=Europe/London:20171130T160000
DTEND;TZID=Europe/London:20171130T163000
UID:TALK96169AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/96169
DESCRIPTION:Co-authors: Pierre-Thomas Brun (Dept. of Ch
emical Engineering\, Princeton University\, Prince
ton\, NJ USA)\, Basile Audoly (Laboratoire LMS\,
Ecole Polytechnique\, Palaiseau\, France) <
br>
Trick roping evolved from humb
le origins as a cattle-catching tool into a sport
that delights audiences with its complex patterns
or &lsquo\;tricks&rsquo\;. Its fundamental tool is
the lasso\, formed by passing one end of a rope t
hrough a small loop (the honda) at the other end.
Here\, we study the mechanics of the simplest rope
trick\, the Flat Loop\, in which the rope is driv
en by the steady circular motion of the roper&rsqu
o\;s hand in a horizontal plane. We first consider
the case of a fixed (non-sliding) honda. Noting t
hat the rope&rsquo\;s shape is steady in the refer
ence frame rotating with the hand\, we analyse a s
tring model in which line tension is balanced by t
he centrifugal force and the rope&rsquo\;s weight.
We use numerical continuation to classify the ste
adily rotating solutions in a bifurcation diagram
and analyse their stability. In addition to Flat L
oops\, we find planar &lsquo\;coat-hanger&rsquo\;
solutions\, and whirling modes in which the loop c
ollapses onto itself. Ne xt\, we treat the more ge
neral case of a honda that can slide due to a fini
te coefficient of friction of the rope on itself.
Using matched asymptotic expansions\, we resolve t
he shape of the rope in the boundary layer near th
e honda where the rope&rsquo\;s bending stiffness
cannot be neglected. We use this solution to deriv
e a macroscopic criterion for the sliding of the h
onda in terms of the microscopic Coulomb static fr
iction criterion. Our predictions agree well with
rapid- camera observations of a professional trick
roper and with laboratory experiments using a &ls
quo\;robo-cowboy&rsquo\;.
LOCATION:Seminar Room 1\, Newton Institute
CONTACT:INI IT
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