Physics%20of%20swimming

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Physics of swimming
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Physics of swimming

• not all fish swim
• not all swimmers are fast or efficient
• but - in order to swim fast, all fish have the
  same constraints due to physics - thus fast fish
  tend to look similar

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Physics of swimming

• Properties of water as medium in which to move
• density - 830x greater than air
• viscosity 70x greater than air

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Physics of swimming

• Properties of water as medium in which to move
• density - 830x greater than air
• viscosity 70x greater than air
• lift force exerted on object perpendicular to
  direction of flow (or movement)
• - proportional to the area over which
  the pressure difference acts

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lift
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Physics of swimming

• Properties of water as medium in which to move
• density - 830x greater than air
• viscosity 70x greater than air
• lift
• drag 830x greater than in air
• - increases with speed of object or current
• - due to separation of flow from object into
  turbulent flow

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Physics of swimming

• Properties of water as medium in which to move
• density - 830x greater than air
• viscosity 70x greater than air
• lift
• drag 830x greater than in air
• - increases with speed of object or current
• - due to separation of flow from object into
  turbulent flow
• boundary layer
• - laminar or turbulent

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Physics of swimming
Reynolds number (Re) ratio of inertial forces to
viscous forces Re LVr/m L length of
object V velocity of object r density of
fluid m viscosity of fluid
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Physics of swimming
Reynolds number (Re) ratio of inertial forces to
viscous forces Re LVr/m L length of
object V velocity of object r density of
fluid m viscosity of fluid flow changes to
turbulent at Re 2,000 turbulent flow is a
consequence of increasing speed increasing
length (decreasing viscosity) (increasing
density of liquid) boundary layer changes to
turbulent as Re goes from 5x105-5x106
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Physics of swimming
Reynolds number (Re) ratio of inertial forces to
viscous forces Re LVr/m L length of
object V velocity of object r density of
fluid m viscosity of fluid Examples of
Re animal speed Re whale 10
m/s 300,000,000 tuna 10 m/s
30,000,000 copepod 20 cm/s 300 sea urchin
sperm 0.2 mm/s 0.03
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Physics of swimming
for efficient swimming avoid separation of
boundary layer from surface maximize laminar
flow in boundary layer
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Physics of swimming
for efficient swimming avoid separation of
boundary layer from surface maximize laminar
flow in boundary layer minimize turbulent flow
in wake
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Physics of swimming
solutions streamline body (tapering)
aspect ratio of about 0.25 maximum
thickness of body 1/3 from front (head)
b
a
Aspect ratio a/b
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Physics of swimming
solutions streamline body (tapering)
aspect ratio of about 0.25 maximum
thickness of body 1/3 from front (head) drag
reduction - keep body rigid
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Physics of swimming
solutions streamline body (tapering)
aspect ratio of about 0.25 maximum
thickness of body 1/3 from front (head) drag
reduction - keep body rigid slime layer to
reduce frictional drag rough surface (cteni)
keeps boundary layer attached?
Australian Museum
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Physics of swimming
Swimming modes kick and glide active -
sustained for hours or days burst - only for up
to 30 secs large fishes have greater difference
between burst and active than small fishes
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Physics of swimming
Swimming modes kick and glide active -
sustained for hours or days burst - only for up
to 30 secs large fishes have greater difference
between burst and active than small fishes
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Physics of swimming
active swimming accomplished using red muscle
along sides of fish - high myoglobin and
mitochondrial enzymes burst swimming with white
muscle - great contractile speeds, low endurance
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BCF - body/caudal fin propulsion
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anguilliform entire body undulates laterally
flattened, elongated body inefficient
Anguilliformes moray eel
Perciformes snake mackerel, etc.
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subcarangiform swim with posterior portion of
body, less than one wavelength tend toward
truncate, rounded, or emarginate tails head
still yaws with motion of swimming aspect ratio
of tail 1.5-2 cods, basses, trout, many others
Salmoniformes rainbow trout
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• carangiform
• less that half to one third of body flexes
• generally narrow peduncle, flared and strongly
  forked or lunate tail
• high aspect ratio tail (square of span/surface
  area) 3.5
• herrings, jacks, some scombrids

Perciformes jacks (Carangidae)
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thunniform extremely stiff body, narrow
peduncle, high aspect ratio tail (4-10) large
tendons to support muscular energy transmission
to tail stiffened tail tunas, marlins,
sailfishes, some sharks
Perciformes tuna (Thunnidae)
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ostraciiform only moves tail, rest
of body rigid boxfishes, porcupine fish
Tetraodontiformes boxfish (Tetraodontidae)
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MPF - median/paired fin propulsion
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rajiiform undulate pectoral fins from front to
back, with wing-like flapping
Rajiiformes Rajidae (manta ray)
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didontiform undulate pectorals for sculling
and maneuvering
Tetraodontiformes - pufferfish (Ostracidae)
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labriform oscillate pectorals for sculling
and maneuvering
Perciformes parrotfish (Labridae)
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amiiform/gymnotiform use undulatory waves
of dorsal (Amia) or anal (Gymnotids) fins also
seahorses, with narrow-base dorsal
Amiiformes - bowfin
Gymnotiformes - knifefish
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balistiform use simultaneous motion
of dorsal and anal fins - triggerfish (used to
some extent in eels, percids, flatfish)
Tetraodontiformes triggerfish (Balistidae)
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tetraodontiform both dorsal and anal
fins move together to each side
Tetraodontiformes ocean sunfish (mola)
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NON-SWIMMING LOCOMOTION gliding above water -
flying fishes add to take-off propulsion by
using tail lobe in water like propeller may fly
up to 400 m, as high up as 5 m may add pelvic
fins as secondary gliding surfaces
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Scorpaeniformes flying gunard
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Other forms of nonswimming locomotion burrowing
- eels, gobies, flatfish, rays wriggling -
eels hitchhiking - remoras, lamprey push-and-hold
- gobies using pelvic disk lamprey using oral
disk
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Other forms of nonswimming locomotion walking
or climbing on pectorals - walking catfish,
mudskippers walking on bottom sea robins using
pectoral rays batfish and relatives
walk on modified pelvics
Perciiformes (Gobiidae) - mudskipper
Siluriformes walking catfish
Lophiiformes - batfish
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Other forms of nonswimming locomotion walking
or climbing on pectorals - walking catfish,
mudskippers walking on bottom - searobins using
pectoral rays batfish and relatives
walk on modified pelvics
Aulopiformes - tripod fish
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Other forms of nonswimming locomotion leaping -
mullets, tuna, sailfish - also salmonids moving
upstream
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Other forms of nonswimming locomotion jet
propulsion - by forcible ejection of water out of
gills by operculum used as assist to fast
take-off by some percids, sculpins passive
drift - larvae, sargassum fish
frogfish