During the experiment I am responsible for making sure that eye protection is worn by me and others around that could be affected by the snapping of the wire. And considering that weights are being suspended from the snapping wire, a floor protection precaution needs to be considered.
Results
The results I will be receiving will reflect on how well I conducted the experiment, I need to make sure that when weights are added to the wire, it is done as gently as possible to avoid the wire stretching unnecessarily, which would lead to poor results.
I will be conducting three experiments using the same apparatus and measurements to avoid a large range in results between the three experiments. I will then be taking an average from which I can then work out stress and strain levels on the wire when different weights are added.
The distance results I will receive will be displayed in an accumulating way, so that I can see how far the wire has stretched from beginning to end.
By doing this also enables me to observe how the experiment is behaving compared to the other experiment. From doing this I can obtain an average of the three experiments, and then work out other things from it such as Stress and strain levels.
Results
After conducting the three experiments I was able to obtain an average, as shown in the table
The information I now have is very helpful, but however not substantial enough to draw a conclusion from. To make it clearer, I need to provide some graphs to my report, which would show much clearer what is happening in the experiments.
On the table I have written, “snapped” for the end result of each experiment. This literally means that the wire has snapped at this point. Unfortunately one of the experiments snapped before the other two, this information would prove to me that either the experiment was carried out differently, poorly, or just that the wire was in different conditions.
Analysis
Firstly a major factor that I investigated which I believed would affect the distance that the wire stretched, was the time period between applying weights. If I applied all the weights at the same time it would snap quickly and results that I would have received would have contradicted each other, by this I mean when each weight is added it wouldn’t have enough time to stretch the wire to its full potential.
To resolve this I applied the weight on a two minute time period, however considering that the first 70 or so Newton’s didn’t have much effect on the wire, I applied them at a slightly faster rate.
The following table shows the relationship between the mass and distance stretched:
As you can clearly see from the graph, the first 50 Newton’s have no effect on the wire, between 50 – 180 Newton’s little change is occurring, but from that point the wire is experiencing large amounts of strain.
Small stress will cause the copper wire to stretch. Remove the stress and it returns to its original dimensions. This is known as elastic deformation. If the stress is increased too far and it passes the point of elastic deformation, the wire snaps. However at this point of elastic deformation the wire yields, from this point the wire begins to deform, this is now plastic deformation.
The information that I now have enables me to calculate other such factors of the physics of the experiment. I can work out stress and strain levels, and then from that, the young’s modulus of the wire. The young’s modulus of the wire tells me how flexible or stretchy the wire is.
Calculations:
Stress = Load / (cross sectional area of the wire)
Cross sectional area of the wire = pie x r (squared)
Cross sectional area of the wire = 0.1075mm(squared)
Stress = x / 0.1075
Strain = Extension / Original Length
Strain = x / 300(cm)
Young’s Modulus = Stress / Strain
I can add the stress, strain and young’s modulus values to my table:
The information I have received from the table will then enable me to provide the conclusion with such arguments as young’s modulus graphs:
The stress-strain graph for the copper wire is pretty much a straight line, up to the point where it fractures. At the point where it fractures the wire experiences plastic deformation this is when the wire cannot be shaped back into its original counterpart.
To show the stress and strain levels acting on the wire most effectively it would be clearer to draw a graph:
The graph above shows the elastic region, the plastic region (extension uniform along length) and the plastic region (necking has begun).
Conclusion
From these results and the way that I have interpreted them I can conclude that the wire behaves to the weight applied to it, in firstly an elastic behavior pattern, then finally in a plastic behavior pattern, depending on how much weight is applied. The more weight applied to the wire, the closer it gets to plastic behavior and eventually snapping. Therefore stress and strain levels upon the wire at these points are behaving differently resulting in a young’s modulus graph, which proves the elastic/plastic behavior patterns.
Some of the results that were recorded may have been affected by human errors such as applying the weights drastically and measuring the distances that wire has stretched incorrectly, but however carrying out the experiment in great detail would take large amounts of time, which would not enable me to compile three experiments and an average.
Ways that my experiment could have been improved: if a weight applying mechanism were used, it would prevent the weights causing noticeable differences to the distance that the wire has stretched. Another problem, which I experienced with the weights, was the fact that more than one slotted mass hook to be applied to the wire. If a device was prepared so that weights were added to the slotted mass alternately to prevent handling the weight to apply the mass.
If I were to carry out the experiment again, I would use a thinner wire, or one with a lower tensile strength. This would mean that less weight is to be applied to the wire. I would do this because if you look back at my results the first 60 or 70 Newton’s don’t affect the wire at all. If the wire is going to snap sooner, it will mean that the wire will stretch less.
