MA-3329 Modern Geometry Name:
____________________________
Fun Paper Model Day #1
So far, we know that in
hyperbolic geometries, triangles' angles add up to less than 180 degrees, and
in elliptic geometries,
triangles' angles add up to more than 180 degrees. In both cases, the difference
between that sum and 180
degrees gives the area of the triangle, up to a constant. For the following models,
however, only the sums of the
angles will be useful to us. Our
elliptic or hyperbolic areas are compressed
down to single points of a
surface, and the remainder of the surface is flat everywhere. Note:
any surface which can be built up from flat pieces of the plane is
called "developable". Spheres
are not developable, but cones are, for example. A cone is flat everywhere
except the tip. Spheres are rounded
equally everywhere and cannot be built up from pieces of the plane. These paper models are special types of
developable surfaces, as are most of your clothing: jeans, shirts, skirts.
Instructions:
1) Look at the models in the
front of the room. What do you notice?
2) Take a couple pieces of
triangular graphing paper and cut darts into them. Either add paper to the
darts, or remove paper, creating ruffles
and/or points. (Ruffles have hyperbolic
curvature while
points have elliptic curvature.) (You may also use one of the extra models
already created.)
3) Draw a triangle on your
surface. You may choose to use the handy
60 or 120 degrees already marked
or you may make the angles however you
like. Measure any remaining angles and
find their sum.
How do your results support or contradict
your predictions based on your observations of the original
models?