We've already noted the prevalence of Canada geese in our area. The other day, as we were walking home, we found ourselves directly under a low-flying gaggle.
Younger offspring: Those geese are flying really close.
Elder offspring: And they're flying in a giant check-mark.
Dr. Free-Ride: Traditionally, that formation is described as a "V". But I guess you're right, one side of it seems to have a few more geese than the other.
Younger offspring: Why do they fly in a "V"?
Dr. Free-Ride: That's a good question. Any thoughts on that?
Elder offspring: In a "V", none of the geese is completely behind another goose. There's one leader, but all the geese can kind of see where they're going.
Dr. Free-Ride: Hmmm, that's true. I hadn't really thought much about that detail. The explanation I always heard was that geese fly in a "V" because it's more aerodynamic for the flock.
Younger offspring: What does aerodynamic mean.
Dr. Free-Ride: Well, it's a windy enough day that maybe I can show you.
As luck would have it, the wind was blowing into our faces on this stretch of the walk.
Dr. Free-Ride: OK, let's walk for awhile shoulder-to-shoulder.
Younger offspring: My shoulders don't go that high!
Elder offspring: She means side-by-side.
Dr. Free-Ride: So, how's the walking?
Younger offspring: It's hard! The wind is trying to blow me backward.
Elder offspring: Yeah, it's almost like being a kite.
Dr. Free-Ride: OK, now let's get into a "V" with me in front and each of you halfway behind me. Now walk!
Younger offspring: There's less wind.
Elder offspring: Most of the wind is going around you, so the space behind you is kind of sheltered from it.
Dr. Free-Ride: "Aerodynamic" has to do with how your shape -- or our shape together -- makes it easier or harder to get through
Younger offspring: It's easier when you're in front of us.
Elder offspring: Yeah, in "V" formation, the person in the front breaks through the wind, and that makes it easier for the ones behind.
Dr. Free-Ride: Shape matters for things like cars, too. Some of those vans that are shaped like big old boxes have a harder time moving through the air than cars that are shaped more like wedges.
Younger offspring: You know what? Paper airplanes with pointy noses go farther than a crumpled piece of paper.
Dr. Free-Ride: That's true.
Elder offspring: I think we learned about wedges in science last year.
Dr. Free-Ride: I think I remember that, too. It's a powerful shape for moving through things, having a narrow edge and then getting gradually wider.
Younger offspring: Each goose sort of has that shape too.
Elder offspring: You mean with the beak and the edges of the wings?
Dr. Free-Ride: That's a good observation. That probably makes it easier for the goose at the front of the "V" than if the goose was shaped like a box or a sphere. Hey, you know that fish do this too, right?
Younger offspring: Fish are aerodynamic?
Dr. Free-Ride: No, I meant fish move in schools for similar reasons to why geese fly in a "V". But they're moving through water instead of air, so you'd probably say they're hydrodynamic.
Elder offspring: Flying fish are aerodynamic.
Dr. Free-Ride: OK, you got me there.
It's worth noting that most domestic livestock seem not to be especially aerodynamic.
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I'm sorry to say you're misleading the offspring by walking in a vee. They're right, they'd be better off behind you than behind and off to one side. Cars and bicycles are the same like that: get behind the cyclist in front and you get the full benefit of the front cyclist's effort.
So what is it that geese are doing? Why don't they fly directly behind each other? Well, us land creatures are pushing straight into the wind, but flying animals are using the wind to create lift, by the simple Newtonian means of pushing air downward. That causes a pair of vortices that cost energy to make, showing as drag. If a goose flew behind another goose, it would be flying in its leader's downdraft, and have to work twice as hard, creating twice as big a pair of vortices. But if it flies to one side, it can fly in the *updraft* of one vortex. Essentially, one of the vortices it makes is cancelled out by the opposite one ahead, causing less drag, because less kinetic energy is being carried away in useless swirl.
And that's why birds fly in a vee and cyclists pedal in single file.
Another way of looking at it is that the two geese become like one goose with twice the wingspan, just as low-drag glider designs have longer wings than more manouevrable, shorter-winged planes. The trick works if the birds are in a vee, a tick, or even just a diagonal line with no bends, and you can sometimes see the birds switching places, moving the bend along the line.
I think if you put that cute little piggy into a meat grinder, it will come out bacodynamic! MMMMM, bacon!
ps: Your kids are smarter and better scientists already that most, if not all, the IDers that I have ever read.
Hydrodynamic aka streamlined
Janet, I just thoroughly enjoy your reconstructed dialogues with your "sprogs"! I helped raise two kids, a boy and a girl, and I wish I had recorded many similar discussions I had with them. Eventually your sprogs will become sullen uncommunicative adolescents; that would be a great time to compile your "sprog-blogging" posts into a book.
I'm sorry to say you're misleading the offspring by walking in a vee. They're right, they'd be better off behind you than behind and off to one side. Cars and bicycles are the same like that: get behind the cyclist in front and you get the full benefit of the front cyclist's effort.
So what is it that geese are doing? Why don't they fly directly behind each other? Well, us land creatures are pushing straight into the wind, but flying animals are using the wind to create lift, by the simple Newtonian means of pushing air downward. That causes a pair of vortices that cost energy to make, showing as drag. If a goose flew behind another goose, it would be flying in its leader's downdraft, and have to work twice as hard, creating twice as big a pair of vortices. But if it flies to one side, it can fly in the *updraft* of one vortex. Essentially, one of the vortices it makes is cancelled out by the opposite one ahead, causing less drag, because less kinetic energy is being carried away in useless swirl.
And that's why birds fly in a vee and cyclists pedal in single file.
Another way of looking at it is that the two geese become like one goose with twice the wingspan, just as low-drag glider designs have longer wings than more manouevrable, shorter-winged planes. The trick works if the birds are in a vee, a tick, or even just a diagonal line with no bends, and you can sometimes see the birds switching places, moving the bend along the line.
It turns out that somebody just did a computational study on that: http://www.arxiv.org/abs/cs/0611032, and both the aerodynamic and the eldest sprog's reasoning look like they're factors in the v-formation. It's kind of cool that she just came up with that on the spot.
An oddment of English for your enjoyment: a group of geese is a gaggle on the ground, but a skein in the sky.
As was conclusively proved in the movie Twister.
Thinking about the Elder Offspring's comments, could visibility be a factor as well? Truck drivers used to get into convoys for reasons of drag reduction; flying in a straight line would seem to offer the most aerodynamic solution as well.
However, pilots flying in formation often adopt a diagonal or V-shaped pattern in order to maintain in-flight visibility, so it seems reasonable to speculate that the V formation used by birds in flight is the best compromise between visibility and drag reduction.
Neat post!
However, I think the word you're looking for is "streamlined."
Count me among those who thoroughly enjoy your science sessions with the "sprogs". I don't know how far you take things, but when the fish came up you could have pointed out that scientifically air and water are both fluids. Thanks for the regular Friday smiles.
What I really like about these sprog conversations is the way they demonstrate healthy human interaction.
Healthy human interaction seems sadly lacking in our hyperindustrial culture. The subculture of science seems to inherit that deficiency, and thus so does the subculture of Scienceblogs.com.
Friday sprog blogging is a weekly bright spot for me. Thanks for demonstrating, consistently, how healthy humans behave.
It's of little value going uphill, or if there's a strong wind from the side.