Fish Shapes and animals
Thrust, Lift, Drag, and Gravity
For a stationary animal in
a moving fluid, air or water, the fluid pushing against the animal exerts a pressure
called drag. The amount of drag depends on the size and shape of the animal.
Streamlined objects disturb the flow of the fluid less and have a lower pressure
drag. If the animal is not to be swept backward it must exert a thrust to balance
the drag. If the animal wants to move forward, its thrust must be greater than the
drag. When a fish undulates its body and tail, a thrust is created. The same
applies to birds, bats, insects and airplanes as they fly through the air. Humans
create thrust when they swim by dragging their arms and legs through the water.
Thrust can also create lift. The thrust that propels a tuna, whale, or porpoise
rapidly through the water is provided by the lift created as its tail oscillates back and
forth.
Viscosity
Fluids such as air and water are different from solids in their ability to flow. How rapidly a fluid flows, or is deformed by a given driving force, is determined by the fluid’s viscosity.
Water is much more viscous than air. For example, at 20?C, the viscosity of water is fifty-five times that of air; the liquid is “stickier” than the gas. Viscosity depends on temperature of both air and water, but in opposite directions. Over the range of 0? to 40?C the viscosity of air increases by about 11%, while over the same temperature range the viscosity of water decreases by 64%. Seawater is slightly more viscous than fresh water.
Moving in Air, Moving in Water
Water’s viscosity has a profound effect on locomotion for smaller organisms like protozoa. These organisms must overcome viscous drag, but they must also rely on viscosity to provide their thrust. The Microscopic Movement exhibit explores how these tiny aquatic organisms get around.
All living things live in a fluid, either air or water. Air is a gas and has no defined shape and no defined volume. Water, a liquid, has a defined volume but no defined shape. The physical characteristic that unifies gases and liquids is viscosity, their resistance to the rate of deformation. For example, a force is required to move a spoon through honey; the faster the fluid is stirred, the more force is required. However, it does not matter how far the honey is stirred; as long as a constant force is applied, the fluid deforms at a constant rate.
Fish Shapes
To reduce the friction of forward motion, most aquatic animals have streamlined bodies shaped roughly like a football. This body shape poses a minimum amount of resistance as water flows over it.
You can tell a lot about a fish’s habitat by the shape of its body. Tuna, which are extremely fast, are shaped like torpedoes. Fish that live in strong flowing streams, like trout and many species of minnows, also have torpedo-shaped bodies that allow them to navigate strong currents.
The elongated bodies of eels and other snake-shaped fish are perfect for slithering through holes or among bottom vegetation, but are not good for fast swimming. A shape like a pancake, with fins sticking out from the body, is good for maneuvering among weed-choked shallows in lakes and ponds or among sharp-edged coral on reefs.
Some shapes have little to do with efficient movements. A number of fishes have rigid, even hard bodies and are decidedly unstreamlined. These slow-moving fishes often produce venom or are extremely well-camouflaged (no need to swim fast for protection) and eat slow-moving animals or hunt by stealth.
Animals
We have chosen the bluegill, the rainbow trout, the bluefin tuna and some microscopic animals for the exhibits on movement.
Bluegill (Lepomis macrochirus) are in the sunfish family, and
are related to bass, crappies, pumpkinseed and others. Lurking in weed beds and
under ledges, these freshwater predators peer out and lunge for smaller fish or a
fisherman’s bait. Also lurking in the same places are largemouth bass.
Bluegills are one of their favorite foods!
Like all sunfishes, the bluegill uses its tail like a fan to dig out a
nest in the bottom of a stream or lake. After the female deposits her eggs in the
nest, the male single-mindedly guards the eggs and chases away all other fish, including
the female.
The bluegill is named for the bright blue patch on each gill
cover. The colors become exaggerated during the breeding season. School
children voted the bluegill Illinois’ state fish.
Rainbow Trout (Salmo gairdneri). This beautiful fish, , is
a native to the western United States, but because of it is so good to eat has been raised
in hatcheries and introduced by the millions into cold streams and lakes around the
world. Black dots pepper the rainbow’s back, tail, fins and the wide red patch
on each side.
Some rainbows live in the ocean and migrate to rivers to lay eggs.
Others live and spawn in cold streams and rivers, where they challenge anglers with
legendary fighting and leaping agility. Rainbows forage on the bottom for
invertebrates and small fishes, or rise to the surface to eat insects or the hopeful
fisherman’s hand-tied artificial fly.
Bluefin Tuna (Thunnus maccoyii) are large, cigar-shaped fish and live near the sea's surface.
The bluefin tuna swims fast (speed bursts of up to 70 km/h have been
recorded) and all the time, even at night. To do this, this tuna must eat a large amount
of food every day. Their diet consists mainly of fish, crustaceans (e.g. krill), and
squid. At various stages in its life other fish, seabirds, sharks or killer whales may eat
the bluefin tuna.
The bluefin tuna can be found throughout the southern oceans of the
world. They are a highly migratory fish and travel long distances throughout their life
cycle. Digital image
from Fishing-World.net There are MANY more neat fish images on their web
site.
There is a wealth of information on the world wide web on fish and fishing. Take a
look at
A list of interesting
fishing web sites.
From the State of Illinois Department of Natural Resources: Fish and Fisheries in the Great Lake Region.
Exhibits
Can we learn from fish? MIT's Robotuna Project
Microscopic Movement: Cilia and Flagella
There are a surprising number of different habitats in a river, many more
than in the still waters of lakes or ponds. Water flow depends on the slope of the
land. Younger rivers tend to have steep slopes, fast-moving water and narrow
floodplains. Older, larger rivers carry more sediment, flood larger areas of nearby
land, and have only periodic rapids or riffles.
Water striders, whirligig beetles and others use the water tension to ride the surface of rivers. Fish swim throughout the water column and some “walk” along the bottom, joined by insect larvae, snails and crayfish. Beaver and muskrat burrow into streambanks, while clams and worms hide among rocks and in sandy bottoms.
Animals react to the flowing water in a variety of ways. Some
have shapes and methods of locomotion that allow them to swim against the current, like
the rainbow trout in the River Olympians exhibit. Some fish that
cannot swim against the current avoid it by staying close to the bottom and behind rocks,
like darters and sculpins. Others, among them bluegills and other sunfish,
congregate in the slow-moving waters under trees and at the inside of bends in the river.
Objectives: Students will observe the relationship between small differences in shape and resistance in water. Students will infer the relationship between streamlining in air and in water. Finally, students will interpret reasons for different fish shapes in varied aquatic environments, and understand that animals and their natural habitats are well matched to each other.
How to use:
Models of trout and bluegills can be inserted into a laminar flowing rheoscopic liquid
which makes the turbulence behind the fish visible. Use the levers to put each fish
into the water (one at a time). Wait for the water to settle down. Look behind
each fish for an area where the white lines get mixed up (use the red dots on the bottom
of the tank to help you remember).
Explanation: Water is much more dense than air. This means that even slight differences in shape can cause a difference in drag. The chunkier fish, the bluegill, causes more turbulence than the sleeker (streamlined) fish, the rainbow trout. The swirled water occurs much more quickly (closer behind the fish) for the bluegill than for the trout.
Physics-Biology Connection: The more streamlined a fish, the less energy it takes to
swim through water. If a fish is less streamlined, it will take more energy to
swim. Air is much less dense than water, so the force needed to move through air is
lower. This means that land animals can have lots of different shapes. Even
so, streamlined land animals move the fastest—like the jaguar.
Robotuna is an example of biomimesis, (biology + mimic) how humans can learn from animals. Using a robotic tuna, scientists at the Massachusetts Institute of Technology are learning to make better designs of ships, submarines, and research vessels. The idea of learning from nature to improve today’s technology is an emerging science called biomimesis. What other kinds of aquatic animals could we base a technology on?
SciTech's Robotuna Exhibit
Objective: The purpose of the RoboTuna exhibit is to encourage students to make the connection between pure scientific research and the eventual development of technologies that help people. It also has a biology message - i.e., how fast different animals move through water - the tuna is one of the fastest.
How to use: Press the black button to start the flow in the tank. Watch the fish’s tail movement and the water around it closely. You should see the vortices (turbulence) created by the fish’s body and its tail. If you are having trouble seeing the vortices, press the orange button to inject dye into the tank to make these vortices more visible.
Explanation: As students observed in the Streamlines and River Olympians exhibits, turbulence normally causes drag, which acts to hamper a fish’s swimming. The tuna is an exception. Tuna use turbulence in the water around them to their advantage.
The tuna senses the pressure differences of the incoming vortices as they move along its side. To capture energy from the vortices, the tuna instinctively times the flapping of its tail to create vortices spinning in the opposite direction. These vortices meet and weaken the incoming vortices. The tuna flaps its tail forcefully in one direction. It quickly follows this flap with another in the opposite direction. When the two vortices meet they combine and create a jet. This produces a strong, sudden thrust and makes the tuna one of the fastest fish around. (Speed bursts of up to 70 km/hr have been recorded.)
Physics-Biology Connections: Our exhibit was inspired by the Massachusetts Institute of Technology’s RoboTuna. Engineers at MIT built a robotic tuna to mimic the movement of the tuna, one of the fastest fish in the world.
Why build a RoboTuna? Think about a modern day submarine.
Even though it is streamlined, it takes a lot of energy to run one. And even though
it is using a lot of energy, it is still a slow and ponderous machine. Now consider
the tuna. Sleek and fast. By researching the way a tuna moves, scientists and
engineers can then try to translate their observations into better technologies. For
example, the scientists at MIT hope to apply what they learn about RoboTuna to research
submarines. Their work can also be applied to many other kinds of ships and
submarines.
How microscopic animals swim: cilia and flagella
Definitions:
How do these one-celled animals move in the water? Amoeba, Euglena, Paramecium
Cilia and flagella are projections from the cell. They are made up of microtubules , as shown in this cartoon. They are motile and designed either to move the cell itself or to move substances over or around the cell. The primary purpose of cilia is to move fluid over their surface. Cilia and flagella have the same internal structure. The major difference is in their length.
Cilia and flagella move because of the interactions of a set of microtubules inside them. This information is from Professor Gwen Childs, University of Texas. For more information see Professor Child’s web page.
SciTech's Microscopic Movement Exhibit
One-celled animals are called protozoa. We feature 3 different one-celled animals amoeba, euglena, paramecium viewed using projection microscopes.
Microscopic Movement enables students to explore how the tiniest of aquatic animals get around, and how a protozoan’s environment both helps and hinders its movement.
Objective: Students will make the connection between viscosity and the action of cilia and flagella. Students will gain an appreciation of the special adaptations that these tiny aquatic organisms have developed to survive and thrive in their environment.
How to use: Press the button to the left of each microscope and observe the slides. The left microscope has preserved slides of protozoa, while the right microscope has a slide of live protozoa.
Left Microscope: Notice the differences between the protozoa. Notice which have cilia and which have flagella. Paramecium has parallel rows of cilia all aligned so that they will beat in the same direction. Can you see them in the picture?
Right Microscope: Notice the different ways the protozoa move. Identify the different types of protozoa in this culture (amoebae, euglena, paramecium). Look at the pictures on the exhibit to help you identify the different types.
Explanation: Protozoa is a type of organism, neither plant nor animal, made up of only one cell. Protozoa have adapted special ways of moving through water. Moving through water is much more difficult than moving through air because the viscosity of water is 70 times greater than the viscosity of air.
Viscosity is the degree to which a fluid resists flow under an applied force. Water is more viscous than air. Protozoa have evolved ways to deal with the difficulty of moving through water. Protozoa have cilia, flagella, or pseudopods that help them move.
Cilia are thousands of tiny hair-like projections that cover the surface of a cell. Cilia wave in a coordinated way to move the protozoa in one direction. A flagella is a long tail-like appendage that is waved back and forth to move the protozoa. Pseudopod means “false foot”. The protozoa extends a pseudopod in the direction it wants to travel. The rest of the body flows into the pseudopod to move the animal.
Newton’s Law is important in understanding how movement is produced by the
action of cilia and flagella. Newton’s Law says that if the protozoan pushes on
the water, the water must push back on the protozoan with equal force and in the opposite
direction. The water pushing on the protozoan is what makes the protozoan move.
Momentum must be conserved. The mass of the water that protozoa move through is
large compared to the protozoan’s mass. The water is barely moving so it has a
small velocity. The protozoan’s mass is very small. Due to conservation
of momentum, the velocity at which protozoa move must be larger than the water’s
velocity:
Physics-Biology Connection: Protozoa move in response to a stimulus. A
stimulus can be food, light, temperature, or chemicals. Cilia, flagella, and
pseudopodia are not only used to produce movement for protozoa. They also help
protozoa eat. Cilia and flagella may be used to sweep food toward the
protozoan’s mouth. Pseudopodia may be sent out to search for food. If
food is found, the pseudopod surrounds the food to trap it so the protozoan can eat.