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J R Soc Interface. 2018 Mar;15(140). pii: 20170901. doi: 10.1098/rsif.2017.0901.

Gyroscopic stabilization minimizes drag on Ruellia ciliatiflora seeds.

Author information

1
Department of Physics and Astronomy, Pomona College, Claremont, CA, USA.
2
Department of Physics and Astronomy, Pomona College, Claremont, CA, USA dwight.whitaker@pomona.edu.
3
Rancho Santa Ana Botanic Garden, Claremont, CA, USA.

Abstract

Fruits of Ruellia ciliatiflora (Acanthaceae) explosively launch small (2.5 mm diameter × 0.46 mm thick), disc-shaped seeds at velocities over 15 m s-1, reaching distances of up to 7 m. Through high-speed video analysis, we observe that seeds fly with extraordinary backspin of up to 1660 Hz. By modelling the seeds as spinning discs, we show that flying with backspin is stable against gyroscopic precession. This stable backspin orientation minimizes the frontal area during flight, decreasing drag force on the seeds and thus increasing dispersal distance. From high-speed video of the seeds' flight, we experimentally determine drag forces that are 40% less than those calculated for a sphere of the same volume and density. This reduces the energy costs for seed dispersal by up to a factor of five.

KEYWORDS:

Acanthaceae; aerodynamics; ballistichory; gyroscopic stabilization; high-speed video; seed dispersal

PMID:
29514987
PMCID:
PMC5908531
[Available on 2019-03-01]
DOI:
10.1098/rsif.2017.0901

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