Forces that act on a fish
As promised (see Fish Gait post), here’s the illustration that shows the various forces acting on a fish when it’s in the water.
As you can see, it’s pretty self-explanatory.
Lift and buoyancy push the fish up towards the surface and gravity pulls the fish down towards the gravitational center of the planet. Most fish control their location in the water column (i.e., how high or low they are in the water) by way of a swim/gas bladder. The more air the fish has in the bladder, the more buoyant it becomes. If a fish would like to move downwards, it can release gas from the swim bladder and become less buoyant.
Sharks do not use a swim bladder. They are buoyant thanks to their livers, which contain a great deal of oil. To change their location in the water column, a shark uses its fins in a special way that involves physics. Something something pectoral fins like airplanes something something. I’d rather not talk about it right now.
Thrust is a fish’s movement forward through the water. The fish’s tail (a/k/a caudal fin) makes a lateral propulsive motion, moving from side to side, and this propels the fish forward through the water. Thrust. Drag is the force the fish must overcome as it moves forward through the water. Something something friction. Something something laws of motion.
O. Keel here is not a force. It’s a ridge on the tail-part (caudal peduncle) that helps to support the caudal fin (a/k/a tail). Makes it stronger and all. Makes the fish better able to work those forces to its advantage.
So yes! Here’s your fish!
This illustration was made by a very talented artist who shall remain nameless at this time. But, if you’d like to give said very talented artist (VTA) some money in exchange for drawings like this one, I’m sure I can arrange something between you and VTA. I can draw up an agreement and everything. I’m legal like that.
fish, thrust, buoyancy, drag, lift, gravity, forces, swim bladder, gas bladder
ps - I’m kidding about making an agreement. That’s a joke about me being a secretary. But the artist is not a joke. He/she/it might be very interested in making drawings or paintings for you. I can maybe hook that up.
July 22nd, 2007 at 2:51 am
Wow, that’s one impressive picture! Well, ok, the article was good too, but the picture rocks.
October 28th, 2008 at 3:43 pm
mmkay, hopefully this is the right blog box thingy…
answer to question!!!:
firstly, gravity(weight/W) is pushing down on the fish from above. A normal(N) force is pushing up against the fish in the form of lift and buoyancy. The fish is going forward, while fluid friction(F) is going against the fish’s movement thus reducing said fishy’s speed. A normal(N) force is reacting against the forward movement of the fishy as well.
poor fishy….
October 29th, 2008 at 1:14 pm
well first there is gravity, or weight, pushing down on the fish as gravity does to all objects. then buoyancy, the normal force, is pushing up on the fish. then you have a friction(fluid) force pushing in the opposite direction at which the fish is moving(swimming). this causes the fish’s speed to decrease.
October 29th, 2008 at 5:41 pm
ONCE MORE WITH FEELING!!!
answer to question!!!:
firstly, gravity(weight/W) is pushing down on the fish from above. A normal(N) force is pushing up against the fish in the form of lift and buoyancy. The fish is going forward, while fluid friction(F) is going against the fish’s movement thus reducing said fishy’s speed. A normal(N) force is reacting against the forward movement of the fishy as well.
poor fishy….
did you get it this time mrs duricky?
October 29th, 2008 at 5:42 pm
answer to question!!!:
firstly, gravity(weight/W) is pushing down on the fish from above. A normal(N) force is pushing up against the fish in the form of lift and buoyancy. The fish is going forward, while fluid friction(F) is going against the fish’s movement thus reducing said fishy’s speed. A normal(N) force is reacting against the forward movement of the fishy as well.
poor fishy….
did you get it this time mrs duricky? i did it 3 to be safe!
October 30th, 2008 at 1:19 pm
ok well gravity(weight/w) is pushing down on the fish. a normal(N) force is pushing underneath agianst the fish in the way of lift and buotancy. the fish will have to use more energy because friction(F) will be acting upon it in the opposite direction
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December 29th, 2008 at 12:17 am
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