How Does Temperature Affect the Behaviour of Elastic Bands?

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An essay on the observations of how temperature affects the elasticity of rubber bands.

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How Does Temperature Affect the Behaviour of Elastic Bands?

  1. 1. How Does Temperature affect the behavior of Elastic Bands? By Rachel McGreevy
  2. 2. Aim The objective of my practical investigation is to find out whether the temperature of an elastic band affects its elasticity, as well as its tensile strength. Before I started the investigation, I carried out some research on what elastic bands are made out, and how and why they act like they do at normal temperature, to form my own hypothesis on the outcome of my experiment. Abstract To test whether temperature of an elastic band affects its behaviour I will be carrying out 3 experiments with 7 different temperatures, ranging from 20 Degrees Celsius to 80 Degrees Celsius. The first experiment will test how the tensile strength of the band will be affected, by testing the breaking weight of the band. The second third experiments will test how the elasticity and extension of the band will change in the same range of temperatures. After carrying out these experiments, I found that the breaking weight, stretch and extension of a rubber band will all increase with a larger change in temperature, and it’s Young’s modulus will decrease. Introduction to Background Physics Elastic bands can be found in almost every household all over the world, varying in size, shape and thickness. Rubber bands are made mainly from a mix of rubber and latex, along with various chemical solutions, which are then poured into an extrusion machine. This extrudes the compounded rubber into a tube shape, which is then set and finally cut width-ways to create the shape of the elastic bands commonly used today1. Rubber is a polymer, which is a chain of interlinked monomers. In particular, rubber is a type of polymer called an elastomer, which is a large molecule that can be stretched to around twice its size, and still return to its original shape. When a force is placed on the elastic band, the tangled up chains of monomers untangle, letting the material stretch. When the force is taken off the rubber band, the chains of monomers tangle up again into their original forms. However, the larger the force on the rubber band the less the molecules will tangle up again2. The entropy of a material is a measure of order of the molecules in a material, where the more disordered the molecules are, the higher the entropy is 3. The equation for entropy, which is also known as the second law of thermodynamics is; ΔS = KLog(W) Where ΔS is the change in entropy of the material, K is the Boltzmann constant and W is the number of possible states for the molecules of the material to be in. When a material is heated, the molecules that the material consists of have more energy and so tend to spread out and travel with more speed. As the molecules spread out, there are more possible states for the molecules to be meaning the value of W increases with temperature, and so the overall value of ΔS increases. Therefore the higher the temperature of the material, the higher the entropy of becomes due to the spreading out and therefore disorder of the molecules. Usually, materials tend to expand when they are heated; however due to the structure of the rubber in the elastic bands which is formed by tangled chains of monomers, when the bands are heated they tend to get smaller in size. This is because the monomers in the material have more energy and are moving around
  3. 3. with a greater speed, and so the chains become more tangled, and so entropy is increased. This means that as the chains are more tangled causing them to pull tighter together, and therefore the rubber band will contract 4. Because the rubber band contracts when heated, the higher the temperature of the rubber band, the harder it is to stretch the rubber band. This should mean that rubber bands at higher temperatures will take more weight to break, but extend less than rubber bands at lower temperatures. We can explain this further by looking at the energy in the elastic band when it is stretched. When an elastic band is stretched, it will seem to heat up. This can be observed by holding a rubber band on your top lip and stretching it. You will notice a positive change in temperature during and for a short time after the stretch. You will also notice that the band will become cooler when it is released from the stretch, as it absorbs heat causing its surrounding environment to cool down. This change in temperature can be explained using Gibbs free energy equation, using the entropy and enthalpy of the elastic band. As explained above, the entropy of a material is a measure of the disorder of the molecules. The enthalpy of a material is the total energy change of the system, from when the elastic band is relaxed to when the band is stretched. Enthalpy is determined by the internal energy of the system, as well as its pressure and volume5. Gibbs free energy equation is known as; ΔG = ΔH – TΔS Where ΔG is Gibbs free energy which is essentially the energy gained or lost in a system, ΔH is change in enthalpy and TΔS is the temperature multiplied by the change in entropy. Before looking at the values of entropy and enthalpy of a system, it is important to know whether it is a spontaneous process or not. A spontaneous process is one where free energy is produced without an external source of energy driving it. In the system of the elastic band, we are stretching it which is a form of external energy, and so the system is non-spontaneous6. Assuming the temperature stays constant for the moment, when the elastic band is stretched, the entropy of the band decreases as the monomer chains untangle, meaning that TΔS is negative (TΔS < 0). In a non-spontaneous process, the change in enthalpy – ΔH – will be a positive value as the energy observed as thermal energy increases as the band is stretched. Using the signs for these two values, ΔG = Positive – Negative, meaning ΔG is a positive value. When ΔG is a positive value the system has gained energy, and as the rubber does not store the energy transferred – or the work done on the elastic band – it is transformed into thermal energy which is why heat can be felt when the band is stretched. When the process is reversed and the elastic band is released from the stretch, no external source of energy is being put into the system when the band goes from a stretched to relaxed state; therefore this system is a spontaneous process. This means that as a reverse of the non-spontaneous stretching process, TΔS is a positive value, ΔH is a negative value and so ΔG will be negative. As the system is spontaneous, the process needs energy to happen, drawing energy from surroundings which will then cool down 7. Now we can use this to look at how the value of ΔG will change with temperature T of the rubber band. When the rubber band is stretched in the non-spontaneous system, the value of ΔG is positive. When temperature T is increased, the value of TΔS
  4. 4. will become larger, therefore increasing the value of ΔG. This means that the energy gained by the system is larger, and so each individual molecule will have more energy. This means that as explained before, the chains of monomers become more tangled, causing the heated rubber band to contract and become harder to stretch. This means that the elastic band is able to take a larger amount of weight before breaking. However when T is decreased, the elastic band will become brittle as ΔG becomes smaller and so will stretch with less force, and therefore should break easier. The Young’s modulus of a material is the measure of its stiffness, and can be defined as the ratio of tensile stress to tensile strain. The equation for Young’s modulus is therefore; E= σ/ε Where E is the Young’s Modulus, σ is tensile stress and ε is the tensile strain on the material. We can also look at the equations for the stress and strain of a material to find a more detailed equation for the Young’s modulus. The stress of a material is measure of average force per unit area of a material the force is acting on. Therefore the equation of stress is; σ=F/A Where σ is the tensile stress with unit N/m , F is force being applied to the material in Newton’s (N), and A is the area of material that the force is being applied to in m 2 2 . The strain on a material is the ratio of the extension of the material in respect to its original length. Therefore the strain equation is; ε = ΔL / Lo Where ε is the tensile strain, ΔL is the change in length of the material – i.e. the new length minus the original length, and Lo is the original length of the material. Therefore we can see that the equation for Young’s modulus 8 can also be written as; E = F * Lo / A * ΔL As we have already found out that change in length should decrease with temperature, then the young’s modulus of the elastic band should increase, as ΔL will decrease, and therefore increasing E. To find out if temperature does affect elastic band in these ways, I devised three different experiments to test out my research. In my experiments, the temperature of the water the rubber bands are soaked in, and therefore the temperature of the elastic bands themselves is the independent variable of all three experiments. The size, shape and thickness of the elastic bands are the control variables, which must not vary to make the tests fair. The breaking weight, stretch and extension of the elastic bands being tested are the dependant variables.
  5. 5. Risk Assessment Object Elastic Band Risk The aim of the first experiment is to force the elastic band to breaking point, so the elastic band will snap each time. This means the rubber band could snap and fly off my direction, and hit my eye, or any part of my body. Weights When the elastic band has reached its breaking point, the band will snap and fall to the floor. This means the weights will also fall to the floor, and as the Lab floor is a hard surface the 100g weights could break away from the hook they are connected to and spill over the floor When the weights fall from the snapped elastic band, the weights have a possibility of hitting mine or other peoples feet, which could causes an injury Retort Stand Water bath Whilst putting the weights onto the elastic band, as I have long hair there is a chance that my hair could get caught on the hook, or stuck in between two of the 100 gram weights. As I could end up putting a large amount of weight on one side of the Retort Stand, there is a chance that it could end up tipping over the edge of the surface. The water in the Water Bath will end up getting very hot, and I will need to retrieve the elastic bands from the water when I need to use them and I could end up burning my hand Precaution To make sure the elastic band does not snap into my eyes, I will be wearing safety goggles throughout all three of the experiments. I will also make sure my clothes cover my body, such as rolling down sleeves to cover my arms. To prevent the hooks breaking I will place two carpet tiles below the hanging weight so when the elastic band finally snaps and the weights hit the floor, the momentum is absorbed and the landing is cushioned. To prevent the weights hitting my feet I will stand to the side of the hanging weights whilst carry out the experiments, and I will not allow others to stand too close to the weights whilst I am carrying out the task. To prevent my hair getting tangled up in the weights, I will tie my hair behind by back to keep it out of the way of the experiment. To prevent the Retort Stand from tipping, I used a G-Clamp to keep the stand on the tabletop in place during the experiments. To prevent from scalding my fingers in the hot water, I will use the wrong end of a spoon to loop an elastic band round the end of it to get it from under the water.
  6. 6. Experiment Number One I devised this experiment to see if the temperature of a rubber band affects the amount of force it is able to withstand before snapping or breaking. Method 1. I first put the Retort Stand at the edge of the table top facing forward, and clamped it to the surface using a G-Clamp facing diagonally, as pictured. Whilst carrying out my preliminary testing, I realised that this wasn’t the most efficient set up as the stand could still tip forward due to the stand being lengthways. I changed the position of the Retort Stand to face sideways and the GClamp to face into the table, which is pictured to the right. 2. I then attached a boss and clamp to the top of the top of the retort stand, which I would hang the elastic band off. I originally placed the clamp facing forwards, but after my preliminary testing decided that it would be better to face the clamp backwards and hang the elastic band off the other end, as the elastic band would have less pressure on it when hanging of the rounded surface, compared to the flat surface of the other end. This change is pictured to the right. 3. I then placed two safety mats on the floor beneath the end of the clamp to stop the weights from hitting the floor when the elastic band snaps to absorb the sound and energy of the collision. 4. I then put 3 elastic bands in a water bath with water at temperature 20 Degrees Celsius which I measured using a thermometer, and waited 10 minutes whilst the rubber bands were in the water to make sure they reached the correct temperature. 5. Once the elastic bands had reached the required temperature, I took them out of the water bath and placed them over the back end of the clamp. After putting on my safety goggles, i then placed 100 gram masses onto the end of the elastic band one by one until it snapped, and I then recorded the result in my lab book. 6. I then repeated steps 4 and 5 turning up the temperature of the water in the water bath by 10 Degrees Celsius for each set of 3 elastic bands. I did this until I reached 80 Degrees, to make sure I had a large range of temperatures to try and get a good set of results.
  7. 7. Before I started this experiment I decided to do a preliminary test using 3 rubber bands at room temperature and so were not heated or cooled in any way. I was surprised at the amount of weight one elastic band was able to hold, and so collected more weights to make sure I did not run out of them for the tests at warmer temperatures. I noticed whilst doing this that in the 3 times that I carried it out, the results differed by a fair amount each time. We can see from the results I gained, which were 5.9 Kg, 6.6 kg & 6.1 Kg, that there is an anomalous result of 6.6 Kg which is a large difference from 5.9 and 6.1 Kilograms. I therefore decided to add an extra column to the results table for this experiment so I could carry out a fourth test for a certain temperature if one of the three results I gained the first time was an anomaly. As I repeat the test more times, the results become more accurate as well as reliable. I also decided during my preliminary testing that I should finish this experiment first with all the temperatures before going on to do the second and third experiments to make sure rubber bands at all of the different temperatures would be able to take at least 1kg of weight before snapping. This was so I could use a 1kg mass to stretch the rubber bands in the next two experiments; otherwise I may have had to start again if the rubber bands were not able to take 1kg of mass which would have ended up wasting time. Experiment Number Two My second experiment was to test how well the rubber bands return to their original length once a force has been applied on them at different temperatures. Method 1. Using the same set up as my first test I put the Retort Stand to face sideways and the G-Clamp to face into the table. I then attached a boss and a backwards facing clamp to the top of the top of the retort stand, which I would hang the elastic band off. The setup is pictured below on the right. 2. I then placed three elastic bands in the Water Bath with water at 20 Degrees Celsius which I measured using a thermometer, and waited 10 minutes whilst the rubber bands were in the water to make sure they reached the correct temperature. 3. Once the elastic bands had reached the required temperature, I took one elastic band out of the water bath and immediately measured its length using a 30 cm ruler. 4. I then looped the elastic band onto the back end of the clamp on the retort stand, and hooked a 1 Kilogram mass on the end of the band and left it hanging for one minute. 5. After 60 seconds had passed, I took the 1 Kilogram mass off of the elastic band, took the band off the reverse end of the clamp and re-measured the length of the rubber band using the same 30cm ruler as before, and recorded the new length in my log book. 6. I then repeated steps 2 to 5 turning up the temperature of the water in the water bath by 10 Degrees Celsius for each set of 3 elastic bands. I did this until I reached 80 Degrees like my first experiment, to make sure I had a large range of temperatures to try and get a good set of results.
  8. 8. I also did a preliminary test for this experiment as well as the first, using 3 rubber bands at room temperature and so were not heated or cooled in any way. The original length for each of the rubber bands was 91 Millimetres each time which leads me to assume is the normal length of the type of rubber band I was using. The lengths of each of the elastic bands after being stretched were all in a similar region; 96mm, 94mm and 97mm. This shows that when the rubber band is stretched it will not completely return to its original length and shape. This experiment should show whether the temperature of the rubber band affects the ability of the molecules in the rubber to recoil into their original shape. Experiment Number Three My third and final experiment was to see how the temperature of the rubber band affected its overall extension. The extension of the band will be the extended length minus the rubber band’s original length, so I will have to measure both of these values for each of the elastic band. Method 1. Using the same set up as my first and second test I put the Retort Stand to face sideways and the G-Clamp to face into the table. I then attached a boss and a backwards facing clamp to the top of the top of the retort stand, which I would hang the elastic band off. 2. I then used a boss to attach a one metre ruler to the end of the reverse side of the clamp with which I would measure the extended length of the rubber band. 3. I then placed three elastic bands in the Water Bath with water at 20 Degrees Celsius which I measured using a thermometer, and waited 10 minutes whilst the rubber bands were in the water to make sure they reached the correct temperature. 4. Once the elastic bands had reached the required temperature, I took one elastic band out of the water bath and immediately measured its length using a 30 cm ruler. 5. I then looped the elastic band onto the back end of the clamp on the retort stand, and hooked a 1 Kilogram mass on the end of the band. 6. As soon as I put the weight onto the band I measured the extended length of the rubber band using the metre ruler, which I then recorded in my log book. 7. I then repeated steps 3 to 5 turning up the temperature of the water in the water bath by 10 Degrees Celsius for each set of 3 elastic bands. I did this until I reached 80 Degrees like my first and second experiments, to make sure I had a large range of temperatures to try and get a good set of results. My preliminary test for this test showed that 3 elastic bands with an unchanged temperature with original lengths of 91mm, 90mm and 91mm extended to lengths of 445mm, 451mm and 444mm respectively. This meant their extensions were 354mm, 361mm and 353mm. This experiment will help me to work out how the Young’s Modulus of
  9. 9. an elastic band changes with temperature, using the extension of the band which I will work out.
  10. 10. Results & Graphs Experiment Number One Temperature of Elastic Band - Degrees Celsius (+/- 1ºC) 20 30 40 50 60 70 80 Breaking Weight Kilograms (+/- 0.01 Kg) 1 2 3 7.80 7.10 7.20 7.00 6.20 6.70 7.40 6.80 6.50 7.50 7.40 7.60 7.50 7.60 9.00 8.00 7.50 8.00 6.40 7.60 8.20 Anomalous Breaking Weight Retest Kilograms (+/- 0.01 Kg) Average Breaking Weight - Kilograms (+/0.01 Kg) 7.00 6.90 6.40 7.80 7.90 7.10 6.87 6.57 7.50 7.63 7.83 7.90 Breaking Weight / Kilograms Average Breaking Weight Of Elastic Bands at Different Temperatures 9.00 8.00 7.00 6.00 5.00 4.00 3.00 2.00 1.00 0.00 0 10 20 30 40 50 60 70 80 90 Temperature / Degrees Celsius Average Breaking Weight Of Elastic Bands at Different Temperatures 8.00 7.75 7.50 Breaking Weight / Kilograms 7.25 7.00 6.75 6.50 6.25 6.00 20 30 40 50 60 Temperature / Degrees Celsius 70 80
  11. 11. Experiment Number Two Temperature of Elastic Band Degrees Celsius (+/- 1ºC) 20 30 40 50 60 70 80 Original Length of Elastic Band - Millimetres (+/- 1mm) 1 2 3 90 90 89 93 93 91 91 90 91 91 93 89 93 92 91 90 91 91 91 91 90 Length of Elastic Band After Force Applied - Millimetres (+/- 1mm) 1 2 3 92 94 93 95 97 95 96 95 96 96 101 103 102 99 96 100 97 98 102 103 99 Average Stretch - Millimetres (+/1mm) 3.33 3.33 5.00 9.00 7.00 7.67 10.67 Stretch Of Elastic Band Stretch Of Elastic Band 10.00 10.00 8.00 8.00 6.00 6.00 4.00 4.00 2.00 2.00 0.00 0.00 Average Stretch of Elastic Band / Millimetres 12.00 10 0 0 20 10 30 20 40 30 50 40 60 50 70 60 80 70 90 80 Temperature of Elastic Band / Degrees Celsius Temperature of Elastic Band / Degrees Celsius Stretch Stretch Of Elastic Band Of Elastic Band 12.00 11.00 10.00 10.00 Average Stretch of Elastic Band / Millimetres Average Stretch of Elastic Band / Millimetres Average Stretch of Elastic Band / Millimetres 12.00 9.00 8.00 8.00 6.00 7.00 4.00 6.00 5.00 2.00 4.00 3.00 0.00 0 20 10 20 30 30 40 40 50 50 60 6070 Temperature of Elastic Band / Degrees Celsius Temperature of Elastic Band / Degrees Celsius 8070 90 80 90
  12. 12. Graph to show how Log of Stretch is Effected by the Temperature of an Elastic Band 2.5 Ln(Stretch) 2 1.5 1 0.5 0 0 10 20 30 40 50 60 70 80 90 Temperature of Elastic Band / Degrees Celsius Experiment Number Three Temperature of Elastic Band Degrees Celsius (+/- 1ºC) 20 30 40 50 60 70 80 Original Length of Elastic Band - Millimetres (+/1mm) 1 2 3 89 81 92 90 88 89 90 91 91 89 92 91 90 89 91 90 94 92 90 89 92 Extended Length of Elastic Band - Millimetres (+/- 1mm) 1 2 3 341 361 339 357 372 380 395 401 412 485 462 465 417 385 426 422 450 435 474 475 466 Average Extension Millimetres (+/- 2mm) Young's Modulus 259.67 280.67 312.00 380.00 319.33 343.67 381.33 12.58 11.64 10.47 8.60 10.23 9.51 8.57 Average Extension / Millimetres Average Extension of Elastic Bands at Different Temperatures 450.00 400.00 350.00 300.00 250.00 200.00 150.00 100.00 50.00 0.00 0 10 20 30 40 50 60 70 Temperature of Elastic Band / Degrees Celsius 80 90
  13. 13. Average Extension of Elastic Bands at Different Temperatures 400.00 Average Extension / Millimetres 375.00 350.00 325.00 300.00 275.00 250.00 20 30 40 50 60 70 80 Temperature of Elastic Band / Degrees Celsius Graph to Show how Log of Extension is Effected by Temperature of an Elastic Band Ln(Etension) 6 5.9 5.8 5.7 5.6 5.5 0 10 20 30 40 50 60 70 80 90 Temperature of Elastic Band / Degrees Celsius Young's Modulus of Elastic Band / Newtons Per Metre Squared Graph to Show How the Young's Modulus of an Elastic Band Changes With Temperature 13.00 12.00 11.00 10.00 9.00 8.00 20 30 40 50 60 70 Temperature of Elastic Band / Degrees Celsius 80
  14. 14. Experiment Limitations I realised after I completed all three experiments and examined these results that there was a problem with the design of my experiment. The temperature of elastic band was not constant after being taken out of the water, due to the heat flowing from the hot elastic band into the cool surrounding air. This meant that the elastic band therefore experiences cooling once it has been taken out of the water bath. This meant that my results were skewed in the extension experiments, meaning all of my results were the reverse of what should have happened. Therefore, as the elastic bands were therefore cooling whilst I was conducting the experiments, I will have to analyse the results I gained thinking about the cooling of elastic bands, rather than their temperature. If I were to re-do this experiment I would have done one of two things. One of the things I could have changed about this experiment was the way I heated up the elastic bands. Instead of placing them in a water bath, I would have placed the weights on the end of the elastic bands for the second and third experiments prior to changing their temperature. I would have measured the length of the band, and then aimed a hair dryer at the elastic band for one minute to heat it up, and then remeasured its length. However, this alternative would also have a few limitations, such as the hair dryer would not heat the elastic band uniformly, and would only be able to heat up to one temperature. The other alternative way to do my experiments that I could have done to improve them is to carry them out whilst the elastic band was submerged in a cylinder of water of the correct temperature. This means that the temperature of the elastic band would be uniform whilst doing the experiment, and the results would have shown correctly whether the temperature of an elastic band affects its temperature. A diagram of this setup is shown below; 30 Centimetre ruler is used to measure how the extended length changes with the temperature of the water A cylinder of water, of which will change temperature throughout the experiment Wooden skewer placed on top of the cylinder of water used to hang the elastic band off The elastic band is hooked round the skewer and submerged into the cylinder, which will change temperature with the water 1 Kilogram mass hooked onto the end of the elastic band
  15. 15. Analysis of Results As mentioned in the limitations of the experiment, the designs of the three experiments carried out meant that my results showed how the decrease in temperature of an elastic band affected its behaviour, rather than showing how the increase in temperature affects its behaviour. This was because the temperature of elastic band started to decrease as soon as it was taken out of the water bath, and cooling down to its original starting temperature. However, in my research I found that if an elastic band is cooled down, the band will do the opposite of what it does when it is heated up which causes it to contract. This means the elastic band will elongate, and so my results will show the opposite of what was expected – how drop in temperature will effect the behaviour of the rubber band rather than how the increase of temperature affects it. When the temperature of the water is increased, the starting temperature of the elastic band submerged in the water is therefore increased. When the elastic band is taken out of the water bath, the heat will leave the elastic band until it has returned to its natural temperature. At larger temperatures, this means the elastic band will have more heat to loose, and will have to cool down further. From experiment number one, we can see that the increase in drop in temperature caused the breaking weight of the elastic band to initially decrease, and then begins to increase. I think the results for the breaking weight at an initial temperature of 40 degrees were a slight anomaly in my tests, which may have been caused by a systematic error, changing the whole set of results. This error could have been caused by the fact that I may have not left the elastic bands in the water long enough, not letting them get up to the same temperature of the water. This would have meant that all of the results would have been smaller than they were expected to be. If we ignore this result and look at the rest, we can see there is a gradual incline in the weight needed to break the elastic band as its drop in temperature – from water temperature to original temperature – increases. This result is what I expected, as during my research I found that the higher the starting temperature of the elastic band is, the harder it is to stretch due to an increase in entropy in heat, and is therefore harder to snap. My second experiment was to test how well the elastic bands would return back to their original size once they have been stretched for a certain period of time. We can see from the results that the results generally have a gradual curve upwards as change in temperature increased. Similarly to my first experiment, the results at 50 degrees Celsius seem to differ greatly from the rest meaning that this is probably an anomalous result. As I repeated the test 3 times, and the each of the results is similar meaning that this anomaly was probably caused by a systematic error, the same one that occurred in my experiment. Not leaving the elastic band in the water for long enough would have meant that the change in temperature would have been less than it was supposed to be, meaning the elastic band would stretch more and so be less able to return to its original size and therefore making its stretch longer than it was meant to be. As the graph of these results was curved, I also produced a log graph to see if the stretch rose exponentially with temperature. However, the graph is not create a straight line, meaning that this relationship is not true, My third and final experiment was to test how the extension, and therefore Young’s modulus of an elastic band changes with temperature. From this I could also work out how the Young’s Modulus of the band differs with an increase in change in
  16. 16. temperature. We can see from the results of the first set of graphs that there is a curved increase in the extension of the elastic band as the change in temperature decreased. However, similarly to the first two experiments, there was a major anomaly at 50 degrees Celsius. As already mentioned this could have been caused by a systematic error by not submerging the bands into the water for long enough and skewing all of the data collected at 50 degrees. However, in all three of my experiments, I have noticed that there has been a large anomaly around 40 – 50 degrees Celsius, which could show that this is the peak temperature of the elastic band where the band is at its weakest. That would explain why the breaking weight was smaller than usual at this temperature of the first experiment, and why the stretch and extension of the elastic band was longer than usual. This could be because at this temperature, the elastic band could start to become deformed, meaning it will break and stretch with less force, and therefore its stretch would be larger than usual as it would be unable to un-stretch to its original size after deformation. As the results of the third experiment show there is a gentle curved increase in the extension, I created a log graph to see if it increased exponentially. As we can see from the graph, the line is not straight, and so the extension does not increase exponentially to the change in temperature. Finally from the results gained by the third experiment, I worked out the Young’s modulus of the rubber bands at the seven different temperatures using the equation stated in the introduction. We can see from the hand drawn graph with the Young’s modulus pointed plotted with uncertainties that the value decreases as the change in temperature increases. This means that the stiffness of an elastic band decreases as change in temperature increases, confirming the information I found out earlier in my research. Conclusions I have learnt a lot about the relationship between an elastic band and its temperature whilst carrying out these experiments for this coursework. The conclusions I have made from my research and experiment results are that the behaviour of an elastic band is affected by temperature in these ways; • • • • • • An un-stretched elastic band will contract when its temperature is increased, and elongate when it’s temperature is decrease An elastic band will give off heat energy when it is stretched, and take in heat energy when it is un-stretched The breaking weight of an elastic band will increase when it’s change in temperature is increased The stretch of an elastic band will increase when it’s change in temperature is increased, as it is unable to return to its original length The extension of a rubber band will increase when its change in temperature is increased The Young’s modulus of an elastic band will decrease when its drop in temperature is increased I have already explained in the section about the limitations of the experiment how I would improve on the experiments I used to achieve the results for this if I were to do it again, to gain more accurate results. However, with the results I did manage to achieve, I believe that my experiment confirmed the information that I found out in my initial research.
  17. 17. Bibliography Ref. Number 1 Reference Type Website Basic Information http://science.h owstuffworks.co m/rubber.htm Website I used this website to find out the structure of rubber and how that affects the behaviour of a rubber band Between 1998-2012, by 3 http://hyperphy sics.phyastr.gsu.edu/hb ase/therm/entr op.html#e3 Website I used this website to find out more about entropy and what it is August 2000, by Georgia State University in America 4 http://www.phy slink.com/educ ation/askexpert s/ae478.cfm Website I used this website to find out about why the temperature of an elastic band changes temperature when it is stretched Between 19952012 by Alex Seeley – Postgraduate Cambridge Physics Student 5 http://www.wis egeek.com/wh at-isenthalpy.htm http://en.wikipe dia.org/wiki/Gib bs_free_energy Website I used this website to find out more about enthalpy and what it is Website I used this website to find out what the Gibbs free energy equation was and basic information about it Between 2003-2012, by Victoria Blackburn Last edited 25.03.2012 7 http://www.you tube.com/watc h? v=ViAmQivKif0 Video I used this video to help to completely understand the Gibbs Free Energy equation and how it works 29.09.2009 8 AS OCR Advancing Physics Textbook Book June 2008 9 http://www.scie ncebuddies.org /science-fairprojects/project _ideas/ApMech _p026.shtml Website I used the AS course text book to remind myself of the Young’s Modulus, stress and strain equations to apply it to my experiments I used the diagram on this website to show I could have redone my experiments 2 6 Reference Title http://www.rub berbands.co.uk /faq/faq.htm I used this website to find out what rubber bands are made of and how they are produced Date Published 2008, By a company called Calibre Craig C. Freudenric Ph.D. 08.10.2010 Evaluation The website is of a rubber band specialist, and so the information is likely to be correct as it would have been written by an expert in the field. Therefore the information is probably fairly reliable. This website is made with the intent of explaining how things work, so the information they give is likely to be correct, and reliable. Although there is no exact publish date on the article, how rubber works will not have changed in this time. The website is that of the Physics department at a University in America so the information will be very reliable, and I also backed the information up using other sources. Although the information was publish a long time ago, the definition of entropy will not have changed in this time. Different websites contradict each other in terms of what happens when elastic bands are stretched. However this was answered by a postgraduate student of Cambridge studying Physics so I thought this would be a reliable answer. This article explained more to do with the chemistry side of things concerning enthalpy in reactions than physics and thermodynamic system, but still useful. Although this article was edited very recently, Wikipedia can be edited by others. The means the information given may not be completely reliable so I had to crossreference it with source number 7, confirming the information was correct. The video is posted on a video account of a teaching school, so the information is probably fairly reliable. The information was explained in detail and was really easy to understand which was a great help. This book was the textbook for the AS part of this course, meaning that is a very reliable source of information. The book was very useful and I gained all the information I needed about Young’s Modulus from it. The diagram shows exactly how I would do my experiment again if I were able to improve it, so was a valuable piece of information

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