* Investigation
* Hold a piece of Waitrose Italian Spaghetti in two clamp stands. Position them so the distance between the place where the spaghetti is attached is 20cm.
* Find the mid point (10cm) from each end and mark it with a pen.
* Hold a ruler in a clamp stand so the 0cm mark is at the same level as the bottom of the spaghetti.
* Hang a 10g mass on the mark made in step 2.
* Measure the deflection (lowest point the spaghetti reaches) on the ruler.
* Repeat steps 4 & 5 increasing the mass by 10g each time until the spaghetti breaks - record the deflection for each mass.
* Repeat experiment for spaghetti lengths of 15cm and 10cm.
Method
Equipment
I will use a ruler with millimeter and centimeter markings so that the deflection and length of spaghetti can be measured to the nearest millimeter; this should provide an appropriate level of accuracy to prove that the deflection is proportional to the mass applied. I will use two clamp stands to hold the spaghetti and another to hold the ruler at a constant level.
* Range
I will carry out the investigation three times to ensure that there are no anomalous results and so an average can be calculated. I will also vary the length (20cm, 15cm and 10cm) to see if different lengths give me more or less accurate readings to use in this investigation.
Analysing Evidence
I have discovered that as the mass hanging from the centre of the spaghetti bridge increases so does the deflection. If the mass doubles the deflection doubles, therefore the deflection is directly proportional to the mass hanging from the centre of the spaghetti bridge. At a point the deflection stops being proportional to the mass because too much mass is stretching the spaghetti.
Therefore I can conclude that the spaghetti bridge behaves according to Hooke's law (deflection is directly proportional to the mass) until the elastic limit is reached. The elastic limit for the spaghetti seems to be inconsistent with the length. The 20cm long spaghetti has an average elastic limit of 33g and the 15cm long spaghetti has an average elastic limit of 27g however the 10cm long spaghetti has an average elastic limit of 47g. This does not seem to be a regular pattern - I would have to carry out further investigation to see if any of the results were anomalous or if a pattern could be established.
As the length of the spaghetti increases so does the deflection. I have noticed that for every 5cm increase in length the deflection increases by 0.1cm (while the spaghetti is still within its elastic limit). So the deflection for each 10g when the spaghetti is 20cm long is 0.3cm and when the spaghetti is 15cm long the deflection for each 10g is 0.2.cm. The total deflection is also higher when the spaghetti is longer.
To explain this I can use a molecular model. The longer the spaghetti the more molecules there are. If the deflection is caused by all the molecules in the spaghetti being pulled apart the same amount then the longer the spaghetti the more molecules are being pulled apart therefore there are more gaps and therefore a larger extension.
I predicted that the deflection of the spaghetti bridge would increase proportionally to the mass applied. If the elastic limit was exceeded then the deflection would no longer be proportional to the mass applied. The conclusion above is exactly the same as my prediction, therefore I can conclude that I correctly predicted the outcome of this investigation.
Evaluating Evidence
I believe that the experiment was successful but some of the results were unexpected/unreliable. When the spaghetti bridge reached its elastic limit some of the deflections were far below the expected curve (See Graphs), especially for the 15cm long spaghetti bridge.
Factors which could have given me unreliable results could have been a flaw in the spaghetti (could have been internally damaged), incorrectly reading the deflection from the ruler or the masses could have been chipped. However, chipped masses should not have significantly affected the results since the inaccuracy in mass would have been negligible.
I believe that the experiment was designed well but there were a few problems. Reading the deflection off the metre rule was cumbersome and I was not always sure if it had been read correctly. It was also difficult to keep the hanging mass in the middle of the spaghetti bridge since it kept moving. To prevent this in future I would attach the mass to the spaghetti using cotton thread tied tightly so it would not move.
To improve the experiment I would find a more accurate way of measuring the deflection. Since using a millimetre marked ruler was cumbersome and the spaghetti was more than 1mm thick therefore it was difficult to decide where to measure the deflection from. I would also find a way of preventing the ruler and hanging mass from interfering with each other since they got in each others way during the investigation.
Additional work, which could be carried out, is to repeat the experiment using, a wider range of lengths of spaghetti. The investigation could also be extended to investigate other factors affecting the deflection such as number of strands of spaghetti, thickness of spaghetti or type of spaghetti.
