07-05-2014, 11:00 AM
Design and Construction of a Spaghetti Bridge
Design and Construction .ppt (Size: 96.5 KB / Downloads: 279)
Why build a spaghetti bridge?
1) To take math and science out of the textbook and into a
project involving design, planning, and construction.
2) Because the process is instructive and fun, and it exemplifies
the difficulties of putting theory into practice.
Math and science? Now I’m worried.
What kind of math and science?
In principle, you can build a bridge without math and science.
But if you want to build one that can carry a maximum load, then
you need to understand the material properties of spaghetti,
the theory of beams, and the physics of canceling forces (statics).
Glues:
1) White glue: Not good. Since it’s water based, the
spaghetti is softened by the glue. Glue joints take
forever to dry. Once dry, joints are not very strong.
2) Model airplane glue: So so. Dries relatively quickly
but is slightly flexible when dry. Glue joints should
be rigid.
3) Hot-melt plastics (glue guns): Easiest to use, but
joints far too flexible.
4) Epoxy: Best solution--especially the 5 minute kind.
Creates rigid joints. Is messy. Requires careful mixing.
Using 5-minute epoxy:
1) Purchase variety in two separate tubes with nozzle tips.
(Double plunger varieties are too wasteful.)
2) Mix epoxy and make glue joints on wax paper. Epoxy
releases from wax paper fairly readily.
3) Mix very small batches--enough for maybe 5 glue joints.
4) Proportions are very important--50 - 50. Too far away
from this ratio and epoxy will never harden. Many
bridges fail because of unhardened joints.