If it would be me I would go down to Lowes and buy a piece of round wood stock and just cut it at different angles to show how a round circle can be come can become the other pieces.
If you can not find a piece of round wood, you could do the same thing with a piece of PVC pipe. After cutting you could sand the rough edges and actually use the Pipe as a stamp; ink it and print the circles, , elipses, and hyperbolas.
Keith Nuttle wrote in news:npa6j6$10p2$ snipped-for-privacy@gioia.aioe.org:
It can't. If you cut a cylinder perpendicular to its axis, you get a circle. If you cut a cylinder at any other angle, you get an ellipse. It is impossible to make a single cut through a cylinder and get either a hyperbola or a parabola.
No can do. You can cut hyperbolas and parabolas from a cone, but not from a cylinder.
That totally and completely misses the point. If they existed, in wood, for something like five or ten bucks (at the most), the google search would make sense.
But the wooden ones are in the hundred-dollar range, which is over ten times the price limit.
I guess I didn't state that from the beginning, so, I apologize for not being clear. The goal was to find an existing "something" that can be sliced into conic sections.
The two best existing somethings are that I have 2-inch diameter fence posts lying around, and I have traffic cones lying around.
So both are free.
My current plan is to put my hand held belt sander in a vise to see if I can sand the fence post into a cone. If that works, I can easily slice the cone with the 12-inch circular chop saw - but the kerf might be a bit wide.
If the kerf is too wide, I can probably jig saw it with a hand-held jig saw, but it might not be a good straight edge.
The great thing about the fence post is that one 8-foot length affords me a lot of wasted scrap! And it's free.
The traffic cones are also free, since I have a few lying around, but they're harder to cut - but they're more visually appealing, if I can manage to cut one. I don't think can double nap the traffic cones though.
So double napping will be best done with the fence post.
If I can find a larger-diameter fence post, I will try that, as 2 inches seems too small to be visually appealing to the room (but it could sit on the teacher's desk).
I don't think a cylinder will work but I guess I could put a cylinder against my belt sander and have the belt sander (in a vise) turn the cylinder into a cone.
Then I could slice the cone into the conic sections.
I have an old 2-inch diameter fence post that I might try that on. I was hoping for a large conic section (like 12 inch diameter) but I can't sand a 12-inch diameter dowel with a belt saw.
Google doesn't find the answer to the question unless the *exact* question was asked.
For example, G. Dubois suggested traffic cones, which would never be found simply by googling for conic sections for a math class.
And, googling for conic sections for a math class finds the stuff that dpb found, which are absolutely gorgeous and perfect - but they cost $100 which is out of the picture.
So, google doesn't always work. It fails when the constraints are different than the norm.
In this case, "cost" is a huge constraint. Theft is also a constraint (where the traffic cone excels).
Size is also a constraint (the bigger the better in this case).
So, my point is that google didn't find that which I seek.
I was hoping to figure out a cheap way to just give them to her, but the ones you showed at that site were gorgeous!
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At $100 each, they're a bit pricey for *me* to spend just to help someone out, and maybe she'd even have a problem expensing them at a public school, but they *are* perfect (and gorgeous!) and made out of wood, which is fantastic.
If I had a lathe, I'd just take a light colored wood and a dark colored wood and make two single-napped cones.
Then I'd slice each cone four ways with a thin jig saw blade (I only have a hand-held jig saw though), and that would be what you see in that picture you found.
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So, with a lathe and a jig saw, it would be easy. But without a lathe, I'd need the cone to exist in a material I could cut (plastic or wood most likely) with a hand-held jig saw or circular saw.
At $30, it's best for the teacher to expense it. So I'll see if they'll let her do that. She's new to teaching and is shy and far too timid (IMHO), since this is a good request, I think, for a math teacher.
Those traffic cones are a GREAT idea for visual aids to show conic sections in a classroom!
For one thing, they're bright orange, and pretty big (so the kids won't steal them) and they're rubbery (so nobody is going to get stabbed by one), and they have a nice base (so they will stay in a corner) and they are visually unusual (so the kids will remember them for decades).
It's probably too hard to double-nap them, but as a single-napped cone, they are a great idea. I even have some spares I can cut open for the kids to see. I'll check that out.
Thank you for that great idea. I knew there were be conics lying around the house!
I once found some nice partial cones in a dumpster outside a textile mill. Spindle cones I think they are called. They were hollow, and the tip was truncated, but they were as cheap as you can get I think.
YOu might even find clay free at an excavation, just look where utility work is being done. Or a hobby shop or a potter supply. Mold it by pushing it into the traffic cone. Cut it with a thin wire.
Or candle wax. Candles come 3 inches thick by a foot high, often for 50 cents at yard sales.
If those fail, plaster of paris from home depot is cheap, pour it into the traffic cones to mold it. 25 pound bag for $11.
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