I have to make a bridge out of spaghetti for my physics class. One problem: we didn’t really learn everything we need to know about tension and compression to do this.
Basically, what I have to is design a bridge between 28 - 35 g. It will be put between two desks, and there will be a 1 kg weight dangled from the “road”. This is the design I’ve been making thus far. However, before I go any further, I’d like to know: will my current design work?
Here’s the design as best I can convey it. Any tips on what kinds of supports I should put within the structure (I cant have anything below the “road”)? My original idea was to set up the “cables” in such a way to lead from the center, to the straight parts, which will be on the desk, hoping that they would transfer the tension to the ther, where the normal force would compensate, but I don’t think that woud’d happen. (ignore the "."s. They’re for spacing purposes in the diagram below and are not an acutal part of the bridge. | \ and / = spaghetti.)
|…/|
|… /.|
|…/…|
|…/…| 8.6 cm
|…/…|
|…/…|
26 cm
(keep in mind this is a view from the side. There will be two of these attached to eachother.)
On previewing, I realize that its sort of hard to tell what I’m talking, so I’ll tell you also. Its basically one noodle forming the bottom piece. Then, on both ends there are 8.6 cm strands at right angles. From the top of those two strands are other strands (about 20 cm) leading to 2/3 the bottom strand. Thus its basically two right triangles, which overlap. On the bottom strand, below where the two overlap, there is another 8.6 cm strand glued onto the first strand to reinforce it, since that’s where the weight will be dangling from (it will dangle 31.75 cm). All strands are attached by a hot glue gun, and the bridge can’t be painted or coated with anything. Will what I’m planning (and have partially done) work?
Are you allowed to look at what other people have done, and to get building hints off the Internet? Or is that cheating? If it’s cheating, then hit your Back button NOW.
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There were 23,300 Google hits for “spaghetti bridge”. Evidently it is Very Hot Stuff in certain circles.
No, I’m not cheating. I collaborated with a classmate and we looked on google this afternoon. It wasn’t helpful since many of the bridges were either two heavy, or violated some other rules (the teacher gave us 2 pages of guidelines.) I appreciate the help, but what I really need to know is whether the bridge I outlined before will work, or if someone could tell me how I could figure that out. Can the structures above the weight disperse its weight? Is it possible to transfer the force of weight exerted from the 1 kg mass from the center, to the sides?
BTW, we’re talking uncooked Ronzoni #8, straight out of the box.
Two points:
[li]Spaghetti’s cheap. If you’re not a procrastinator, throw a couple together this weekend and test them yourself.[/li][li]Using the tension from the pillars is a time-tested and sound method of supporting the bridge deck. However, you usually have tension from the opposite side of the pillars, to prevent their bending or snapping. In this case you can’t really anchor the ends, but it may be worthwhile to consider putting an “upper deck” to brace pillar against pillar. I assume the weight attachment is threaded through, rather than lowered onto, the structure.[/li]
Some other questions:
[li]How much contact will there be with the desk at each end? []How many full strands does your current plan use, and how many full strands are possible given the weight requirements?[/li][]Is your score based on success with 1 kg, or total weight held, or weight ratio?
How many strands of spaghetti are there in 35 g ? How much mass can a bridge made out of a single strand support ? Your rules probably disallow glueing 35 grams of spaghetti into a single stick, but if you did would it carry a 1 kg weight ? How many strands would it take to do that ? Your bridge needs to be at least that strong, and you can get some idea of whether it is by counting the number of tightly connected strands crossing the gap. Your design looks like it might need some sort of compressive beam between the two peaks. Else the spaghetti in your uprights is liable to break when it bends too far. You might consider angling your uprights so as to put a compressive force on the roadbed as weight is applied. Giving the roadbed a slight upward curve (unloaded) would ensure that the compression transfered from your uprights serves to counteract the downward force of the load.
The key to any design using a brittle material like spaghetti is to look for its strengths and weaknesses. Spaghetti is really weak/brittle when bent, but its torsional(?) strength (push/pull on the strand) is pretty strong. Consider this in your design…
dqa: I cant put in pillars, because there can be nothing below the road.
squink: Thanks. One strand of spaghetti is about one gram. Although the teacher will apply weight until it breaks, 1 kg = 100 (this project is 10% of our grade.) I’ll look into what you said.
