Spaghetti Bridge Lab

Block 6, Group 6, 8/27/13 Aleksi Arostegui, Blossom Wong, Rebecca Harvey
By: Rebecca Harvey

Pre-Lab Notes:

• Testing variables independently is essential
• Independent variable - variable purposefully changed by the experiment
• how many marbles, spaghetti strands
• Dependent variable - variable that responds to change in independent variable
• distance of cup from floor, how many marbles it takes to break (strength)
• Controlled variables - variables that stay constant
• bridge set-up (length of spaghetti, cup and string, books)

Purpose: Our purpose is to test how the number of thin strands in a spaghetti bridge will affect the strength of the bridge.


Prediction: If there are more strands of thin spaghetti in the spaghetti bridge, then the bridge will be stronger and able to sustain more weight.


Materials:

• Thin spaghetti strands
• Cup
• Marbles
• String
• Supports (table)

Procedure:

1.     Set up supports by pushing two tables together until they are 6 inches apart

2.     Attach the string across the top of the cup so that the cup hangs from the string.

3.     Place one strand of thin spaghetti evenly across the gap between the two tables. Put tape in the spots where the spaghetti is resting to mark the exact spot to place your bridge.

4.     Hang the cup from the center of the thin spaghetti strand.

5.     Place marbles in the cup, one at a time, until the spaghetti bridge breaks. 

6.     Record how many marbles it took for the bridge to break.

7.     Repeat steps 3-6 five more times, adding one more string of spaghetti to the bridge each time, for a total of six trials.

Data Collection: 

Data Analysis: great!

       Verbal Model: As the number of spaghetti strands in the bridge increases, the strength of the bridge increases proportionally.

       Math Model: strength = (4.5143 marbles/strand)(spaghetti) - 0.8 marbles

       Explanation of Slope: The slope means that one strand of spaghetti has the strength in order to hold, on average, 4.5 marbles, and for every 1 strand of spaghetti added to the bridge, 4.5 marbles are able to be sustained and added to the collective strength of the bridge.

       Explanation of y-intercept: The y-intercept means that when there are no spaghetti strands, the bridge can obviously support no weight, because the strength is zero. Our y-intercept as very close to 0, meaning that our data was very close to what it should have been.

Conclusion:

       The purpose of this lab was to test how the number of thin spaghetti strands in a spaghetti bridge would affect the strength of the bridge. In order to test this, we set up a bridge using thin spaghetti strands placed over a six inch wide gap between two tables. We then suspended a cup from the bridge by a string and placed marbles into the cup until the spaghetti bridge broke. We repeated this experiment five more times, each time adding a strand of spaghetti to the bridge.
       My prediction was that the more spaghetti strands in the bridge, the stronger the bridge would be. We found that this was an accurate prediction; as the number of spaghetti strands in the bridge increased, the strength of the bridge increased proportionally. We found the exact equation to be: (strength) = (4.5143 marbles/strand)(spaghetti) - 0.8 marbles. The slope, or 4.5143, meant that as the spaghetti increased by 1, the strength of the bridge would increase by 4.5143 marbles; that is, proportionally. Our y-intercept should have been at 0, due to the fact that a spaghetti bridge with no strands can support no marbles and therefore has no strength. However, -0.8 is very close to 0, meaning that our data was most probably very close to accurate.
       Our data was markedly different than many of our classmates'. This was to be expected, however, due to the fact that not everyone was testing the same variables with the same control groups. For instance, some groups used thin spaghetti, like us, but some used regular (thicker) spaghetti strands. We also used marbles as units of measurement while other groups used hex nuts. The distance between supports was not controlled across all groups, and some groups taped their bridge to the table, while we did not. This disparity in controlled variables across the groups led to very different results.
       Indeed, we should not have gotten the same results because each group was doing a different experiment when it came down to the details. In this experiment I learned that the details and the differences in "controlled" variables are extremely important in order to have consistent results. but the general trend was the same
       There are several small things that could have, and probably did, go wrong in our procedure. For instance, we did not account for the weight of the cup when calculating results. This weight would have affected the breaking point of the bridge, and therefore the results. We dropped the marbles in the cup from non specified heights. This was not only inconsistent, but by dropping the marbles instead of placing them gently in the cup, we likely added further stress to the bridge. And finally, it remains unlikely that all the spaghetti strands used in this experiment were uniform in thickness and strength. This would have affected the strength of the bridge, and is very difficult to measure. Out of all these errors, the dropping the marbles in the cup seems like the easiest to fix. With that example, we could focus, next time, on gently placing them at the bottom of the cup. The weight of the cup could be accounted for in calculations, however, it would still have an effect on the breaking point of the bridge. The inconsistency of the strength of individual spaghetti strands is the one error that is the least possible to fix, because there is no way of ensuring that each spaghetti strand is identical.  excellent!
       Proportionally - having a consistent ratio or relationship between two factors as they increase or decrease
       Trendline - a line on a chart that expresses and predicts the average movement of the variables being analyzed
       Variable - a condition or factor that can be manipulated, either by the manipulation of other variables or directly, to show change in a lab experiment
       This lab was extremely detailed, requiring everything to be written down exactly as the structure dictated, with very little room for exploration or unexpected results. It was a very predictable lab, with a rigid structure and very little spontaneity. I appreciated the simplicity of the procedure, but at the same time I felt like I was working very hard on something not very interesting. I realize that this was a tester lab, in order to familiarize us with the designated format, but I hope that in the future, there will be more opportunities to explore and be surprised by the scientific principles being demonstrated. I totally understand where you are coming from, and I think you'll like it better next lab!  :)  great job!