The factors affecting tensile strength Essay Example

The factors affecting tensile strength Essay Example The factors affecting tensile strength Paper The factors affecting tensile strength Paper I am comparing four sets of data. My data will be categorical. There is a simple statistical test which looks at the difference between observed and expected values and relates them to a probability level, thus making it possible to identify how likely it is that the values are significantly different. This test is called the Chi squared test. Precautions to ensure reliability   We are assuming ethnic background does not affect our results. It will not cause a massive variation in our conclusion.   All hair samples must be taken from 16-18 year old females. 6 different samples must be taken for each colour of hair. Make sure all equipment is set up; ensuring the strand of hair is fastened to the shown equipment correctly. (Figure 5). * Each hair is tested five times, so I am repeating the experiment, to make my results reliable and more accurate. Results (My own (raw data) results will be highlighted in dark red on tables 2, 3, 4 5). (The letter B is used in my results to show where the hair broke). Investigating the factors affecting tensile strength of human hair Analysing: (Skill C) Calculations Strength is determined by the amount of stress a hair can withstand without breaking. To work out the strength of each hair I calculated the stress applied to each when breaking. To do all the calculations I used the following formulas: 1  I calculated my values to do the statistical test. Discussion Melanin molecules are proteins, which are produced at the root of each hair. The more melanin in your hair, the darker it will get. An amino acid called tyrosine is converted into melanin so the hair will have colour. First, the bodys blood vessels carry tyrosine to the bottom of each hair follicle. Then, in this melanin factory tyrosine is used as the raw material for the production of the natural melanin that is the colour in hair. In short, natural hair colour depends upon the presence, amount and distribution of melanin, a natural pigment found in the cortex. All natural hair colours are created from two types of melanin. Eumelanin = black pigment Pheomelanin = red/yellow pigment Mixed melanins = when both eumelanin and pheomelanin mix together inside one melanin granule. The natural colour of the hair is decided by: a) What type of melanin is in the hair b) How much melanin is in the hair c) How closely packed or scattered the melanin is within the cortex. The type of melanin and the size of the granules determine whether hair will be brown, blonde, ginger or black. The amount of melanin and its distribution determine how dark or light the hair colour will be. Black hair is created from granules full of eumelanin densely packed in the hairs cortex. Brown hair, depending on its cool or warm tones and its darkness or lightness, is created either from granules filled with eumelanin and more sparsely distributed along the cortex than those of black hair, or granules filled with a blend of mixed melanins. The red/yellow pheomelanin is believed to cause the warm, golden, or auburn tones found in most brown hair. Blonde hair has a very low melanin content. And while scientists have not yet determined which is dominant, it is believed that eumelanin creates blonde hair. Melanin in blonde hair is so sparse that what we actually see is the colour of the hair fibre itself, keratin, which is a pale yellow, off-white shade. Granules filled with pheomelanin create Ginger hair. The pheomelanin in ginger hair is less densely packed in its granules. Its shape is somewhat more irregular than its black counterpart, eumelanin. It is slightly rounder and more spread out. From my results I found out that brown hair needed the greatest amount of force to break. Blonde hair needed the least amount of force to break. Black hair was second strongest and ginger hair was third strongest. The order of strength (from my results) of hair is as follows: Brown, Black, Ginger, and then Blonde. Brown hair stretched the most before breaking. Blonde hair stretched the least before breaking. Black hair stretched the second furthest and ginger hair stretched the third furthest. The order of length of hair stretched (from my results) before breaking is as follows: Brown, Black, Ginger, and then Blonde. Brown hair experienced the highest strain before breaking and blonde hair experienced the lowest strain before breaking. The order of strain experienced by hair (from my results) before breaking is as follows: Brown, Black, Ginger, and then Blonde. Brown hair experienced the highest tensile stress value before breaking and blonde experienced the lowest tensile stress value before breaking. The order of tensile stress experienced by hair (from my results) before breaking is as follows: Brown, Ginger, Black, and then Blonde. Graph 1 shows the average force required to break the four colours of hair. From this graph I can see that brown hair required the greatest force to break. Black hair also required a large amount of force to break and so did ginger hair. Black hair only required a small amount of more force to break then ginger hair. The breaking force required for brown, black and ginger hair was quite similar. Blonde hair required much less force to break compared to the other colours of hair. This proves that the disulphide bonds in the blonde hair are not a big advantage for strength of the hair. The darker the hair the stronger the force required for the bonds in the hair to break. The darker the hair the more resistant it is to breaking when forces are applied. The darker the hair the higher concentrations of melanin present along the hair cortex. The same sort of pattern is seen in graphs 2, 3, 4 and 5. Graphs 2, 3, 4 and 5 show the extension of hair when masses are added. Blonde hair breaks the earliest and brown hair breaks the latest. Graph 2 shows brown hair. Brown hair requires about 120g to extend up to about 70mm before breaking. The graph follows a basic trend and there are no anomalous results. All results fit the line of best fit. Graph 3 shows blonde hair. Blonde hair requires about 80g to extend up to about 35mm before breaking. The graph follows the basic trend and most results fit the line of best fit. There is one anomaly, though. The extension should not increase and then decrease. It should keep on decreasing. There must have been an error in recording this result. The results in graphs 2, 3, 4 and 5 are all averages. To work out the blonde values in table 32, the results in tables 12, 13, 14, 15, 16 and 17 were used. There was only one value for the extension at 80g, in table 15. This value was smaller than the average of all the extensions in all six tables. This sample of hair should have broken at 80g not 90g. This did not happen. This may have been an error in not measuring correctly. Graph 4 shows ginger hair. Ginger hair requires about 100g to extend up to about 60mm before breaking. The graph follows the basic trend until it gets to 55g point. From this point onwards the hair length increases and decreases dramatically. This should not happen. The reason why this happens is described above with the blonde hair. It is an error in measuring. Graph 5 shows black hair. Black hair requires about 140g to extend up to about 65mm before breaking. This graph is perfect. There are no anomalies. All points meet the line of best fit accurately. Graph 6 shows the average stresses and strains experienced by each hair colour. All four hair colours are plotted on the same graph so they can be easily compared against each other. Brown, blonde and ginger hairs do not follow the normal trend. The stresses and strains for these three should continue to increase. Tables 57, 58, 59 and 60 show where the stress and strain values came form. The results are like this because when the stress and strain values were calculated the average extensions were used, which had a few faults, as describe above. Graphs 7, 8, 9 and 10 show clearly what is happening to the stress-strain curves. Graph 7 shows one anomalous result. It has a high stress and strain value. Graph 8 also shows only one anomalous result. These two graphs show the basic trend. Graph 9 shows the normal trend until the stress value gets to 150Nm-2. Then it decreases and goes back on itself. This should not happen. The reason for this is explained above. There is an error in the extension averages. Graph 10 shows no anomalies. Graphs 11, 12, 13 and 14 show modified values for stress and strain in all colours of hair. Graph 11 shows the modified stresses and strains for brown hair. This graph does not bend backwards and the stress and strain values do not decrease. Graph 12 shows the modified stresses and strains for blonde hair. This graph does not show values of stress and strain decreasing. Graph 13 shows the modified stresses and strains for ginger hair. This graph has changed a lot. It reads much clearer. Stress and strain increases throughout. This is exactly what the graph should look like. Graph 14 is the same as graph 10. It did not need any modifications. The toughness of a hair is measured of its resistance to break. A lot of energy is required to break a tough material. Finally, the strength of a material (or tensile strength) is the greatest tensile stress it can undergo before breaking. Hair is an elastic material; it can stretch to a certain maximum point (elastic point) before breaking. The largest tensile stress that can be applied to a material before it breaks is known as its ultimate tensile stress (UTS). This value is sometimes referred to as the materials breaking stress. Graph 7 shows the stress-strain points for brown hair. Graph 11 shows a modified version of this. The UTS for brown hair is 359. 03. Graph 8 shows stress-strain points for blonde hair. Graph 12 shows a modified version of this. The UTS for blonde hair is 125. 48. Graph 9 shows the stress-strain for ginger hair. Graph 13 shows a modified version of this. The UTS for ginger hair is 286. 58. Graph 10 shows the stress-strain points for black hair. Graph 14 shows a modified version of this. The UTS for black hair is 158. 31. Overall I can see that brown hair was the strongest. This was not expected. I expected black hair to have the highest tensile strength, as it had a higher density of melanin along the cortex. Blonde hair turned out to be the one with the lowest tensile stress. Ginger haired people have a high density of the pheomelanin pigments in their hair fibre. Those who produce virtually no eumelanin have a red to orange colour depending on the density of the pigment in the hair fibre. Red haired people who have a greater relative proportion of eumelanin production have a deeper red to red brown colour. Ginger hair also should have a high tensile strength. This is what I saw in my results. Black hair should also have a high tensile strength. My results showed black hair to have high tensile strength but not the highest. There are other ways in which hair tensile strength could have been measured. Hair products like shampoos have an effect on hair tensile strength. They are now designed to change hair strengths. Different makes of hair shampoos could be used. Strength could be measured in a similar way to how I measured it. A control will be also be needed, with hair with no products added. These modifications in Graphs 11, 12, 13 and 14 show what the stress strain graphs should look like. In Graphs 7, 8, 9 and 10 the lines should not bend backwards. Statistical Test I will be using the (Chi squared test) X2. The formula for the Chi squared test is as follows: X2 = ? [(O E) 2 /E] O = Observed value E = Expected value The ((O E) 2) part of the formula considers the size of the difference between the observed and expected values. This difference could be either positive or negative. To avoid the mathematical problems associated with negative values, the difference is squared. The (E) part of the formula relates the size of the difference to the magnitude of the numbers involved. The sigma (? ) sum symbol is required because there is not just one pair of observed and expected values, but several (in this case four). By taking all the observed values of stress from tables 57, 58, 59 and 60, I can work out the expected value for each hair colour. I can then place these values in a table and work out the value for X2, using the chi squared formula. To calculate the degrees of freedom to be used can be found as follows: Number of categories minus 1. In this case: 4 1 = 3 The critical value (taken from critical values for the Chi squared test) at 3 degrees of freedom is 7. 81 (at the 5% level). The test statistic (X2 = 94. 235) is greater than the critical value(C. V = 7. 81, at the 5% significance level). We therefore can reject the null hypothesis and state there is a significant difference between the observed a Investigating the factors affecting tensile strength of human hair Evaluating: (Skill D) Limitations The selotape holding hairs in the paperclip at the top and at the bottom could have interfered with the tertiary structure of the protein, keratin. This could have increased or decreased the bond attractions in the hair to cause the hair to have a high or low tensile stress. This would make my results unreliable. The hairs showing higher tensile stress may just be showing how sticky the selotape is and how strongly it is holding the hair structure together. This though, would affect all my results, as all hair samples had selotape on them to hold them together at the top and at the bottom. So, this limitation would affect all hairs making it a very weak limitation. My conclusion will not be affected as this limitation affects all hairs.   The time in between weights were added is another limitation. When each weight was added the hair stretched. But when there were a lot of weights on hair, the hair stretched quickly and then the length was measured. After I finished measuring the hair had slowly stretched a little bit more. So the measurement was wrong. When the next weight was added extra extension was added onto the new extension. My results were affected by this because some extensions were false making some data imprecise. Therefore, my conclusion will be invalid, because some hair samples could have broken at lower weights if I had waited for the hair to stretch, very slowly until it broke. There needed to be a time limit in which I had to record the extension of the hair, before adding the next weight to the hair. The eye piece graticule can be a limiting factor. Different people measured hair thickness and recorded it to what they felt the thickness ought to be according to the scale. It was not very clear to see how thick the hair was, as the hair was faded under the microscope at all magnifications and the outline was difficult to see. This could affect my results as the thickness of hairs was used to calculate the cross sectional area of the hairs, which was then used to calculate the tensile stress experienced by the hair. This could make my tensile stress values incorrect. My conclusion therefore could be affected; by making out that a certain coloured hair had a higher tensile stress than another coloured hair, when really it shouldnt have. This would make my conclusion unreliable.   There were different shades of hair colour, for example, there were light brown hair colours and dark brown hair colours. It was sometimes hard to distinguish between brown and blonde. This was the same for blonde hair. This would have an affect on the reliability and precision of my results making the accuracy of the strengths of different colours of colours of hair inaccurate. There should have been a certain shade of colour of hair (same amount of melanin in each brown hair) used for each colour sample. My conclusion will be imprecise because brown or blonde hair shades could cause incorrect results and make my conclusion incorrect.   The 10g mass is a limitation as the hair could break at lower masses than they actually did, for example a hair that broke at 50g could have broken at 41g, but I wouldnt know that as I only used 10g masses. So, I got false readings implying the hair is stronger than it actually is. If smaller masses were used my results would be much more accurate to make my conclusion reliable. This limitation could cause my conclusion to be invalid, causing the hairs strength and point on breaking higher or lower than it actually is. Conclusion After doing my statistical test I can reject my null hypothesis and accept my hypothesis and say that brown, blonde, ginger and black hairs differ in tensile strength. I have proved this difference in my calculations, mainly in graphs 1 and 6. From my results I can see that darker coloured has a higher tensile stress compared to lighter coloured hairs. In my hypothesis I said that lighter coloured hair would have a higher tensile strength than darker coloured hair, due to lighter coloured hair having sulphur-sulphide bonds, which are very strong. I have disproved this. Through testing all four colours of hair I can see that these strong sulphur bonds do not reflect any tensile strength qualities. Lighter coloured hair does not have an advantage over dark coloured hair when it comes to tensile strength. It mainly depends on the type of melanin the hair contains. The denser the melanin quantity is the stronger the hair.