Investigate the difference between the strength of bridges made from flat and round building materials
What You Need :
• 8 marshmallows • 18 pieces of raw spaghetti • 4 pieces of raw linguine (spaghetti and linguine should be same diameter) • 1 paper clip • 1 envelope and a scissors (to make hanging basket for coins) • approximately 40 coins • paper and pencil to record observations To Do and Observe
1. Cut off the lower corner of the envelope for your coin basket. 2. Unbend one end of the paper clip to make a hanger and poke it through the top of your coin basket. 3. Construct two pyramids of equal size with your marshmallows and spaghetti. 4. Connect the pyramids with a single strand of spaghetti. 5. Hang your coin basket from the bridging piece of spaghetti. 6. Add coins one at a time to the basket. 7. Record the number of coins in the basket at the time the bridging spaghetti breaks. 8. Repeat the experiment three more times to get an average number of pennies needed to break the spaghetti bridge. 9. How do you think the results will change if you use linguine for the bridge instead? 10. Test your hypothesis by repeating the experiment with the linguine as the bridge. 11. Was the round (spaghetti) or flat (linguine) shape stronger?
What's Going On
Circles are among the strongest shapes in nature. External and internal stress distributes itself evenly throughout a round structure. Spaghetti has a shape like a cylinder, while linguine is shaped like a flattened rectangle. A piece of spaghetti has the same strength in any direction it is bent. Linguine will bend more easily in one orientation than another. Instructions: Spaghetti Bridge Be sure to experiment using pieces of spaghetti and linguine with similar diameters. And try orienting each piece of linguine in the same direction; this will produce a more uniform strength throughout the structure.
Tip
• Have your class experiment with constructing different shapes using linguine and spaghetti. Which shapes work better with which designs?
Bridge Building @ the Deutsches Museum http://www.deutsches-museum.de/ausstell/dauer/bruecken/e_brueck.htm Other Experiments on TryScience www.tryscience.org/experiments/experiments_home.html
Each group is to build a bridge made from spaghetti and glue/epoxy. The object is to construct a bridge that will carry the heaviest load while still meeting specifications. Bridges will be loaded until they fail.
RULES:
1. The bridge is to be built from spaghetti (cylindrical forms of pasta) and glue, epoxy or resin.
2. The bridge shall be free-standing and must span two level surfaces which are one meter apart.
3. The support for the bridge shall be from the top of the level surfaces. The edges of the level surfaces cannot be used in any way for support.
4. The bridge must include a decking of spaghetti to provide a suitable road surface at least 5cm wide across the full span of the bridge. Three conditions must be met:
a) gaps in the bridge deck are not to exceed 2 mm,
b) a block of wood (5 cm x 5cm x 10 cm) representing a car must be able to move along the length of the decking unobstructed from end to end,
c) the deck of the bridge must not be more than 5 cm above or below the ends of the bridge at any point along its length.
5. You must incorporate a "loading platform" consisting of a U-bolt secured to a piece of plywood (0.7 cm x 5 cm x 10 cm). This platform is to be attached at the center of the bridge such that the bottom of the U-bolt is no more than 5 cm from the top of the bridge decking. All loads will be suspended from this U-bolt, and there must be a clear space directly below it to allow loads to be attached. Loads will be attached using an S-hook, and, if necessary, a 10 mm diameter metal rod extension. If during loading, the bridge twists in such a way as to cause the bridge to touch the rod at any point other than the U-bolt, thus lending additional support, the bridge will be disqualified.
6. The maximum vertical depth of the bridge, from the highest point in its structure to the lowest cannot exceed 50 cm.
7. The maximum weight of the bridge including the loading platform must not exceed 0.75 kilograms.
Note: These rules are essentially the same as those developed for contests at Okanagan University College. For a bridge meeting these restrictions, Okanagan claims a world record of 176 kg.
Rules - Mini Version
Each group is to build a bridge made from spaghetti and glue/epoxy. The object is to construct a bridge that will carry the heaviest load while still meeting specifications. Bridges will be loaded until they fail.
RULES:
1. The bridge is to be built from spaghetti (cylindrical forms of pasta) and glue, epoxy or resin.
2. The bridge shall be free-standing and must span two level surfaces which are a half-meter apart.
3. The support for the bridge shall be from the top of the level surfaces. The edges of the level surfaces cannot be used in any way for support.
4. The bridge must include a decking of spaghetti to provide a suitable road surface at least 5cm wide across the full span of the bridge. Three conditions must be met:
a) gaps in the bridge deck are not to exceed 2 mm,
b) a block of wood (5 cm x 5cm x 10 cm) representing a car must be able to move along the length of the decking unobstructed from end to end,
c) the deck of the bridge must not be more than 5 cm above or below the ends of the bridge at any point along its length.
5. You must incorporate a "loading platform" consisting of an eye-bolt secured to a piece of plywood (0.7 cm x 5 cm x 10 cm). This platform is to be attached at the center of the bridge such that the bottom of the eye-bolt is no more than 5 cm from the top of the bridge decking. All loads will be suspended from this eye-bolt, and there must be a clear space directly below it to allow loads to be attached. Loads will be attached using an S-hook, and, if necessary, a 10 mm diameter metal rod extension. If during loading, the bridge twists in such a way as to cause the bridge to touch the rod at any point other than the eye-bolt, thus lending additional support, the bridge will be disqualified.
6. The maximum vertical depth of the bridge, from the highest point in its structure to the lowest cannot exceed 25 cm.
7. The maximum weight of the bridge including the loading platform must not exceed 250 grams.
Note: These rules are essentially the same as those developed for contests at Okanagan University College. For a bridge meeting these restrictions, Okanagan claims a world record of 176 kg.
Building a spaghetti bridge is an educational experiment that demonstrates how bridges work. The steps here give you the basic information you need to design and build your own spaghetti bridge. If you participate in a spaghetti bridge building contest, the contest rules are likely to specify allowable materials, the size of your bridge and how it will be judged. Success is typically determined by how many times its own weight your bridge can hold without breaking. Thus, your goal is to build a lightweight bridge that can support a heavyweight load.
Instructions
Things You'll Need:
Raw spaghetti (a bridge three feet long requires about two pounds of pasta)
White glue or a hot glue gun
Rubber bands
Graph paper
Cellophane (clear plastic wrap)
1.Step 1
Build supports for your bridge. Bundle several strands of pasta together in the shape of a tube. Apply glue to each strand as you go. Hold each bundle together with a rubber band until the glue dries.
2.Step 2
Build a deck for your bridge (also known as the roadbed--the part of the bridge upon which the load will be placed). Two possible designs are: 1) A round bundle of unglued spaghetti (the lack of glue allows the spaghetti to shift as needed under the weight of the load), or 2) Several layers of spaghetti, with each layer consisting of pieces of spaghetti glued side by side to the width of the deck, and the resulting layers glued one atop another to form a thick stack (try 10 layers for starters).
3.Step 3
Design the trusses (also referred to as the substructure and superstructure) of your bridge to scale on a piece of graph paper. This will serve as a template for the building of your bridge. The best designs consist of a series of triangles, which are stronger than squares.
4.Step 4
Cover the graph paper with a sheet of cellophane (clear plastic wrap). This allows you to see your template as your build your bridge, without getting glue on the graph paper.
5.Step 5
Cut the spaghetti to fit the template, lay it out on the template and then glue them together using white glue or a hot glue gun.
6.Step 6
Glue all the components of your bridge together (supports, deck, and trusses).
7.Step 7
Gradually add weight to your bridge in small increments to determine how much weight it can hold before it breaks.
Tips & Warnings
Experiment with making trusses using various triangle-based constructions. Try forming trusses based on the shapes of the letters M, W, V, and inverted V.
A triangle that points down is more stable than one that points up.
Bridges must withstand the forces of both compression and tension. These forces are optimally balanced when the top and bottom of the truss are made up of more material than the center (usually triangular) portion, because the top and bottom are subject to the most compression and tension, respectively.
We need model experiments to test different constructions before you build the real thing. This is how engineers work. You don't want to have your bridge collapse the first time someone walks on it. The main point is that the material that you use for testing in the small scale model behaves exactly like the stuff (in this case steel) in the real bridge.
And here the spaghetti comes in. Spaghetti in a model bridge is just as strong as the steel in the big one. If you want to understand more about testing the strength of scale models read here:
Scale, Size and Mass
Let's say your model is 50 times smaller than a real bridge. Now don't forget: your model is not only 50 times shorter, but also 50 times less wide and 50 times less high! (You have seen the same problem with the Weigh a Dinosaur experiments.)
Now suppose you want the real bridge to carry 20 trucks weighing 10,000 kg each. Your model must then be able to carry a load that weighs 50 x 50 x 50 = 125,000 times less!
Ten trucks together weigh 200,000 kg. Divide this by 125,000 and you get 0.16 kg = 160 grammes. That's how much your model must at least support before it breaks.
Use different numbers for your own model.
We will have lots of fun doing the experiments and the results really surprise you. After many tries, you'll find a construction that is many times stronger than the bars just tied together. Here is a description of the experiments.
Why not try them yourself?
Spaghetti Bridge Experiment
We want the make a clever construction that is stronger than a single piece of spaghetti (or, a steel bar in the real thing). First, we need to know how much load a single one can carry before it breaks, and then compare it with our construction.
We test the spaghetti pieces like this. Rest the piece on two supports and tie a weight to its centre (see picture). Have several weights ready with various masses, for example 10, 20, 50, 100, 250, 500 grammes etc., whatever you can find. Start with 10 g and with each next step increase the load by adding another weight. At each step measure how much the spaghetti bar has bent. The photos and the film make it clear how this is done. Put your measurements down in a table.
Carry on adding mass until the piece breaks. Now you know how strong one spaghetti piece is. If you want to do a really good job measure a few more pieces of spaghetti, to see if some are stronger or weaker than others. Make a note of the load that an average piece can support, for instance 12.7 grammes.
Experiment also with the distance between the supports. If they are too far apart the piece will bend and slip off before it breaks. But you will find that out soon enough.
If you set the supports closer you will find that the spaghetti can carry heavier loads. Make several tests with the supports, say, 15, 12, 9 and 6 cm apart. You will need these later when you compare the strength of your construction with the strengths of the single pieces.
Make some final tests with a bundle of spaghetti, e.g. five or ten. Find out that together they are indeed five or ten times stronger than a single one. Check also what happens if you glue them together. Are they now stronger or weaker?
Constructions
Let's have a look at real steel constructions, for instance railway bridges or crane arms. You will see they all are somehow put together as series of triangles.
Try out different constructions by glueing together a few spaghetti. The best way to do this is to use a glue gun (see photo). This is an electric gun, which melts bars of plastic. When you apply it, the hot glue cools quickly and immediately binds two pieces together. No waiting.
Now find out why triangles are such clever things to build bridges and cranes with.
First, cut a number of spaghetti exactly the same length. You will need lots and lots of them. So, start making 50 pieces 5 cm long and 25 pieces 7 cm long. Or, if you plan to make a bigger bridge, 10 and 14 cm, respectively.
Glue four 5-cm long pieces together to make a square. Make another square, now with a 7-cm long piece connecting opposite corners. Test both constructions by squeezing them in the direction of the arrows. You see that the square built of two triangles is much stronger. It doesn't even make much difference whether you press in the direction of the red or the green arrows.
Now for the real thing. If you connect a number of triangles you can make a beam that is strong and light at the same time. Like this:
Let's try out different constructions. There are different ways to make a bridge from a series of connected triangles. Here you see several examples, which we called, M-, W-, V- and inverted-V-constructions:
A W-construction.
A V-construction.
An inverted-V-construction.
For our bridge we also need something to walk on, a bridge deck. We tested a bundle of 10 whole spaghetti pieces and also 10 pieces glued together.
The bundle bends and the pieces start breaking one after the other.
The ten that weren’t glued rearranged themselves and formed a round bundle that could carry a load of 400 grams. Yet, the spaghetti glued together were only able to carry a load of 300 grams. Probably the outer 2 spaghetti pieces carried the heaviest part of the load and collapsed relatively fast. The load was so great that the spaghetti started to bend:
We found out that the best construction was the “M-construction”. This beam could carry the heaviest load of all our constructions: up to 400 grams! The construction took 17 spaghetti pieces. Now, 17 times the strength of one spaghetti would only be able to carry 160 grams of load. So, our construction is 2.5 times stronger than just the pieces it was made of! This was much better than we had expected.
We wanted to test a model of a bridge that you can walk on. So we created a simple bridge with two “M-constructions” with decks on top and at the bottom each of 10 bars glued together. For this bridge we used 28 whole spaghetti bars that separately would be able to carry around 0.64 kg. Some testing with the construction gave us 2.75 kg for the maximum load. This was more that the 2 x 0.64 = 1.30 kg we had expected.
The bridge that Arie and Marc finally tested.
Here you can see a film of one of the tests we did:
Now it is up to you! We are sure that you can create a bridge that can carry an even heavier load. Try making it lighter yet stronger than our bridge. You can start a contest with your friends or class mates.
Some tips:
It makes a difference: apex up ur down!
a triangle with the apex down is more stable than one with the apex on top (figure)
you can use sheets of lasagne for the bridge deck
An arc bridge. Make your own bridge design and test its strength.
try different designs (see figure). Some may be stronger than the straight beam structure. Use your imagination.
So ...
We test the spaghetti pieces like this. Rest the piece on two supports and tie a weight to its centre (see picture). Have several weights ready with various masses, for example 10, 20, 50, 100, 250, 500 grammes etc., whatever you can find. Start with 10 g and with each next step increase the load by adding another weight. At each step measure how much the spaghetti bar has bent. The photos and the film make it clear how this is done. Put your measurements down in a table. 
Try out different constructions by glueing together a few spaghetti. The best way to do this is to use a glue gun (see photo). This is an electric gun, which melts bars of plastic. When you apply it, the hot glue cools quickly and immediately binds two pieces together. No waiting. 
Glue four 5-cm long pieces together to make a square. Make another square, now with a 7-cm long piece connecting opposite corners. Test both constructions by squeezing them in the direction of the arrows. You see that the square built of two triangles is much stronger. It doesn't even make much difference whether you press in the direction of the red or the green arrows. 
