Physics of swimming

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

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

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

lift

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

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

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

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

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

Physics of swimming for efficient swimming avoid separation of boundary layer from surface maximize laminar flow in boundary layer

Physics of swimming for efficient swimming avoid separation of boundary layer from surface maximize laminar flow in boundary layer minimize turbulent flow in wake

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

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

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

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

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

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

BCF - body/caudal fin propulsion

laterally flattened, elongated body inefficient anguilliform entire body undulates laterally flattened, elongated body inefficient Anguilliformes – moray eel Perciformes – snake mackerel, etc.

cods, basses, trout, many others 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

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)

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)

ostraciiform only moves tail, rest of body rigid boxfishes, porcupine fish Tetraodontiformes – boxfish (Tetraodontidae)

MPF - median/paired fin propulsion

rajiiform undulate pectoral fins from front to back, with wing-like ‘flapping’ Rajiiformes – Rajidae (manta ray)

undulate pectorals for sculling and maneuvering didontiform undulate pectorals for sculling and maneuvering Tetraodontiformes - pufferfish (Ostracidae)

labriform oscillate pectorals for sculling and maneuvering Perciformes – parrotfish (Labridae)

amiiform/gymnotiform use undulatory waves of dorsal (Amia) or anal (Gymnotids) fins also seahorses, with narrow-base dorsal Amiiformes - bowfin Gymnotiformes - knifefish

balistiform use simultaneous motion of dorsal and anal fins - triggerfish (used to some extent in eels, percids, flatfish) Tetraodontiformes – triggerfish (Balistidae)

tetraodontiform both dorsal and anal fins move together to each side Tetraodontiformes – ocean sunfish (mola)

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

Scorpaeniformes – flying gunard

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

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

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

Other forms of nonswimming locomotion: leaping - mullets, tuna, sailfish - also salmonids moving upstream

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