Investigatin the properties of cling film
...will hold the cling film in a tight, secure position. 2. Using a Stanley knife I will cut a piece of cling film, which will be 100mm in length and 40mm in width. 3. Then with scissors I will cut a piece of tape, which will be 80mm long, which will be wrapped around the cling film. 4. Then I will piece a hole in the tape, which will be used to put the masses on 5. Then I will slide the top end of the cling film 5mm into the clamp and I will fasten the cling film within it. 6. Then using the hole that I created in the tape, which is wrapped around the cling film I will add masses, which will go up to, a 100g and I will take the readings after every weight that is added. 7. I will use a Vernier Caliper to measure the extension of the cling film. Measuring the extension of the cling film may have caused a parallax error. To minimize this I tried to keep eye level with the edge of the cling film throughout the experiment. Results: Masses/g Extension/mm 0 0 5 0.5 10 1.0 15 1.5 20 2.0 25 2.5 30 3.0 35 4.0 40 4.5 45 5.0 50 6.0 55 7.0 60 7.5 65 8.5 70 9.5 75 10.0 80 11.0 85 12.0 90 13.0 95 13.5 100 14.5 Problems I had to overcome: 1. Clamping the cling film caused holes in it and hence it ripped as the forces were applied. To overcome this I placed a piece of masking tape between the clamp and the cling film. I adapted the design to solve the problems. Whilst taking down measurements to minimize errors. I carried out the experiment three times. This would enable me to get an average result. Each time using a different piece of cling film which measured 40mm in width by 100mm in length. Each time I measured the extension from the bottom of the cling film, which I marked blue in order for me to see it better. The Young’s Modulus For all materials: the ratio of stress to strain is a constant. This is the same as saying that many solid materials as well as springs obey hook’s law. So for the materials that obey the law we can predict the effect of applying tensile forces whatever the size or shape of the object made from the material. Tensile forces are longitudinal forces, which tend to stretch the material and pull it apart. The ratio is called the young’s modulus of the material. Young’s modulus, E=tensile stress Tensile strain Strain has no units, so the young’s modulus has the same units as stress, namely Nmˉ². We have seen that: Stress=F/A (force/Area) And Strain= x/L (extension/ original length) Putting these expressions into the equation for the young’s modulus we have: E=F/A / x/L =FL/Ax (in Nmˉ²) Therefore to measure E, we must measure the extension x that is produced by a tensile forces F on an object of length L and of a cross-sectional area of A To obtain a force against extension graph I had to convert my masses (g) into forces (N). Force=ma (a=acceleration due to gravity) but weight=mg (a=g) Therefore I concluded that force=weight F is proportional to weight F=ma (mass in g, a=9.81N/kg) Looking at the basic shape of the force against extension graph I can see the curve is for an elastic material. Due to this behavior cling film can said to be elastic. The curve shows that before it reaches its elastic limit, point x on the graph it obeys Hooke’s law (f=kx). If the cling film were unloaded at between the points o-x it would return to its original length and shape. However, if it is loaded beyond this point then the material becomes permanently deformed. I concluded that cling film behaves in a similar way to rubber under tension. They both weep continuously but after the elastic limit, necking occurs. This is when the materiel gets thinner where the greatest force is. This is usually created in the middle of the material. Due to this conclusion I decided that I would investigate the molecular behavior to give me a better understanding of why cling film behaves the way it does. My finding showed that cling film undergoes polymerization. This polymerization reaction is between ethane (CH=CH) monomer to form the polymer polythene. Due to the long chain molecules of the carbon-carbon the attraction between the c-c are weak Vander waals forces. This weak force enables them to slip easily over one another due to the stress that is needed to straighten them out. I can conclude from my research that the reason why cling film behaves like rubber when force is applied it due to the fact that polythene is a combination of the elasticity of rubber and the plasticity of some metals. Like, rubber initially when the cling film is stretched it is not stiff. This is because the molecular chains are unraveling and lining up. As the strain on the cling film gets larger it becomes stiffer. I looked over the results I obtained after my experiment and I noticed that the cling film showed signs of weep. I think this was due to the time that the weights were left on and the time for the measurements to be taken. From the time taken to place on one mass and then the other, I noticed that the cling film did not stop at a certain point but continued to stretch. The time taken for me to place a mass and gain an accurate result varied for each time I placed a mass. This caused some inaccuracy in my results. To improve this I decided to perform another experiment. This time I will apply a particular mass to the cling film and measure the extension over a set period of time. The apparatus is set up as before with the addition of a stop clock. I carried out the experiment three times to gain accurate results. From observation and analysis of my results and graphs, the mass against extension graph for experiment 1 has a nice positive linear line. The gradient of this line is 6.67 which means that this is 6.67g per mm. Results: Mass/g Extension/ mm1 2 3 Average Extension/ mm 0 0 0 0 0 10 1.0 1.5 1.0 1.2 20 1.5 2.5 1.5 1.8 30 3.5 4.0 3.0 3.5 40 4.5 5.5 3.5 4.5 50 6.0 6.5 5.0 6.8 60 8.0 8.0 7.0 7.7 70 9.5 10.0 8.5 9.3 80 11.5 12.0 10.5 11.3 90 13.0 13.5 12.0 12.8 100 14.5 15.0 14.0 14.5 Investigation on the effect of a slit in a piece of cling film Aim: Testing to see how changing the size of a vertical and horizontal slit in a piece of cling film will affect the force needed to break the cling film. Finding how increasing the size of the vertical and horizontal slit to see the forces cling film undergoes when it breaks. Prediction: My prediction is that as I increase the size of the slit horizontally the force needed to break the piece of cling film will decrease because the surface area will decrease however for the vertical slit in a piece of cling film, increasing the size of the slit will not have a major change in the force that is needed to break the cling film because it doesn’t affect the cross sectional area. Apparatus: Ø Stopwatch Ø Ruler Ø Sets of 10g Masses Ø Boss clamp Ø Stand Ø Cling Film Ø Scissors Ø Stanley Knife Ø Clamps Ø Sticky tape Diagram of Apparatus: Method: 1. The equipment will be set up on the bench. I will attach a boss clamp to the stand and to the boss clamp I will place resting on top of the boss clamp the clamp, which will hold the cling film. 2. Using the Stanley knife and scissors, I cut correctly to scale the sizes of cling film that I will need. 3. Then the slit was manufactured into the cling film. There were two directions that the slit could have gone one were vertical and one was horizontally but both were in the middle of the cling film and the slit increased by 5mm in each experiment. 4. Then I opened up a clamp and inserted the cling film 5mm into the clamp and I clamped one side of the cling film by the clamp. 5. Then on the other end of the cling film I needed something light enough so that it does not stretch the cling film very much but something strong enough that when I put the masses on it the material can hold it. So I used sticky tape, as this is strong, light and it can be attached to the cling film easily. What I did was I got a 80 mm piece of sticky tape and I wrapped the longest side around the cling film and I put the width of the tape 5mm on the cling film which gave me space on the bottom of the tape to put a hole where I was able to hang the masses off. 6. Then I got a boss clamp and attached it on to the stand and with the clamp that I used to hold the cling film I attached that to the boss clamp which held the cling film suspended in the air. 7. Masses would then be added to the clamp and the mass required to break the cling film could be calculated then from the masses the force could be worked by the equation F=Mg where F is the force, M is the mass and g is the gravity which is 9.8ms-2. However during the experiment some problems arose. · The cling film kept braking near the clamps. Where the cling film kept braking near the clamps I decided to put masking tape in between the clamps so that it would not damage the cling film because this way the surface area is larger on the points which means it will be harder for the clamp to pierce the cling film. Since cling film had a low breaking force I used masses, which were 10g instead of very heavy ones such as the 100g masses. I also repeated the experiments three times to ensure better accuracy in the experiments and in the results. The results are shown below Force needed to break cling film when there is a Horizontal slit manufactured into it. Slit/mm Mass needed to break Clingfilm/g1 2 3 Average Mass needed to break Clingfilm/g 0 190 185 185 187 5 175 170 170 172 10 130 135 140 135 15 120 120 125 122 20 110 105 110 108 25 80 75 75 77 30 60 55 50 55 Using these results I was able to calculate the force required to break the cling film. The equation for the force of the cling film to break is as follows: Force Cross Sectional Area = Stress Tensile strength = Breaking point of cling film As I knew the cling films cross-sectional area I could accordingly enter that into the equation: I measured the cross sectional area of the Clingfilm by multiplying the length by the width of the Clingfilm. Cross-Sectional Area= Length x Width Now using the mass value I had to change this into force using the formula: F=Mg (a=acceleration due to gravity which is 9.81 N/kg) Below shows a table of where I incorporated the masses into the forces Horizontal Slit/mm Test1/kg(x10-3) F=Mg 1/N Test 2/kg (x10-3) F=Mg 2/N Test 3/kg(x10-3) F=Mg 3/N Average Mass/kg(x10-3) Average F=Mg /N 0 190 1.86 185 1.81 185 1.81 186.7 1.83 5 175 1.72 170 1.67 170 1.67 172 1.69 10 130 1.27 135 1.33 140 1.37 135 1.32 15 120 1.18 120 1.18 125 1.23 121.7 1.19 20 110 1.08 105 1.03 110 1.08 108.3 1.06 25 80 0.78 75 0.74 75 0.74 76.7 0.75 30 60 0.59 55 0.54 50 0.49 55 0.54 Vertical Slit/mm Test 1/kg(x10-3) F=Mg 1/N Test 2/kg(x10-3) F=Mg 2/N Test 3/kg(x10-3) F=Mg 3/N Average Mass/kg(x10-3) Average F=Mg /N 0 190 1.86 185 1.81 185 1.81 187 1.83 5 185 1.81 180 1.77 180 1.77 182 1.78 10 180 1.77 180 1.77 175 1.72 178 1.75 15 175 1.72 170 1.67 180 1.77 175 1.72 20 170 1.67 170 1.67 170 1.67 170 1.67 25 165 1.62 170 1.67 165 1.62 167 1.63 30 160 1.57 155 1.52 160 1.57 158 1.55 Horizontal Slit/mm F=mg 1 /N Stress/N/m² F=mg 2 /N Stress/N/m² F=mg 3 /N Stress/N/m² Average F=Mg /N Average Stress/N/m² 0 1.86 465 1.81 452.5 1.81 452.5 1.83 456.7 5 1.72 430 1.67 417.5 1.67 417.5 1.69 421.7 10 1.27 317.5 1.33 332.5 1.37 342.5 1.32 330.8 15 1.18 295 1.18 295 1.23 307.5 1.19 299.2 20 1.08 270 1.03 257.5 1.08 270 1.06 265.8 25 0.78 195 0.74 185 0.74 185 0.75 188.3 30 0.59 147.5 0.54 135 0.49 122.5 0.54 134.8 Vertical Slit/mm F=Mg 1/N Stress/N/m² F=Mg 2/N Stress/N/m² F=Mg 3/N Stress/N/m² Average F=Mg /N Average Stress/N/m² 0 1.86 46.5 1.81 45.25 1.81 45.25 1.83 456.7 5 1.81 452.5 1.77 442.5 1.77 442.5 1.78 445.8 10 1.77 442.5 1.77 442.5 1.72 430 1.75 438.3 15 1.72 430 1.67 417.5 1.77 442.5 1.72 430 20 1.67 417.5 1.67 417.5 1.67 417.5 1.67 417.5 25 1.62 405 1.67 417.5 1.62 405 1.63 409.2 30 1.57 392.5 1.52 380 1.57 392.5 1.55 388.3 Now that I had obtained the force results for the experiment I now needed to find by how much percentage the cling film with the horizontal slit broke before the vertical slit. Now I used the equation= Average force needed to break the cling film with a horizontal slit Percentage Average force needed to break the cling film with a vertical slit x 100= difference From the results and the equation it can be clearly seen that if a slit was marked on cling film horizontally the cling film would break with less force then the cling film with a vertical slit. This must have had an impact on the formula. Force (N) Cross Sectional Area /m² =stress N/m² Then I found out that cling film with a horizontal slit made the value in the cross-sectional area decrease whilst the cling film with the vertical slit did not affect the cross-sectional area. This is because the slit had an impact on the cross sectional area leaving the areas either side of the slit to be the true cross sectional area. The vertical slit affected the width of the cling film but this isn’t in the formula to work out the cross-sectional area so this is the reason why a vertical slit in cling film took more force to break it then the horizontal slit. The horizontal slit weakens the material because this causes stress concentration areas where the force on the material is very great because this force is being applied to a small area which causes the material to tear and eventually break. I also went on to find the stress for the cling film with the horizontal slit was under and I came up with the equation: Force (N) 100x10ˉ³ x (40-5) x 10ˉ³ /m2 =stress N/m² Force (N) 3.5x10ˉ³/m2 =stress N/m² Again I found the equation for the stress the cling film for the vertical slit was under and I came up with the equation: Force (N) Cross Sectional Area /m2 =stress N/m² =Force/N 4x10ˉ³ = stress This shows that the cling film is almost at the same amount of stress when it breaks. It would because it took less force at a smaller cross sectional area for the horizontal slit cling film to break under and more force at a bigger cross sectional area for the cling film with the vertical slit to break under so the forces must equal around the same and my results say it did. This shows that the cling film has a breakage constant-a certain value at which the cling film breaks at. Since a 5 mm slit was impressed on a 100mm long and 40mm width piece of cling film, the cross sectional area was affected by approximately 1/8th as 1/8th of the width of cling film was taken away when the cling film was slit. Moreover, if the slit were to increase by size, I would therefore conclude that if the size of a horizontal slit in relation to the cling film were to increase the force needed to break the cling film would decrease. Thereby making the size of the horizontal slit in ratio to the Clingfilm indirectly proportional to the force needed to break the cling film. From observation and analysis of my results and graphs you can see that the horizontal slit line has a slightly steeper line compared with the vertical slit line. These lines are shown to be negative because as the slit increases the force needed to break the pieces of Clingfilm decreases, this is due to the fact that as the slit is enforced, the slit will cause crack propagation which will make the slit tear easily due to the fact that it is causing a high pressure force on a small area. The horizontal line is steeper because it is affecting the cross sectional area, which means that the force needed to break the cling film, will decrease if the cross-sectional area decreases. The gradient of the vertical slit line is 9.09x10-3 and the gradient of the horizontal slit line is 0.04. This shows that there is 9.09x10-3 N of force per mm acting on the Clingfilm for the vertical slit line and there is 0.04N of force per mm acting on the cling film for the horizontal slit line. Experiments on the length and width of cling film. Aim: Testing to see how changing the length and the width of a piece of cling film will affect the force needed to break the cling film. Finding how increasing the length and width of a piece of cling film affects the force that the cling film undergoes when it breaks. Prediction: My prediction is that as I increase the width of the material I think the force needed to break the cling film will increase as I am affecting its cross-sectional area whereas for changing the length I don’t think there will be as much of an increase in force needed to break the cling film because there is not much of an affect on the cross-sectional area. Apparatus: Ø Stopwatch Ø Ruler Ø Sets of 10g Masses Ø Boss clamp Ø Stand Ø Cling Film Ø Scissors Ø Stanley Knife Ø Clamps Ø Sticky tape Diagram of Apparatus: Method: Now I tried to see if the length and the width of the cling film had any affect on the elasticity of the cling film. The experiments are similar to the first experiment in the way that it is the same roll of cling film but this time I will be changing the length and width of the piece of cling film. For the experiments, where I will be changing the length the widths will always be the same size but with experiments to do with the widths the widths would change and the lengths would stay the same. Force needed to break cling film when the length of the cling film is changing. Length/mm Test 1/kg(x10-3) F=Ma/N Test 2/kg(x10-3) F=Ma/N Test 3/kg(x10-3) F=Ma/ N Average/kg(x10-3) Average F=Ma / N 20 390 3.82 380 3.72 380 3.72 383 3.75 40 440 4.31 450 4.41 440 4.31 443 4.34 60 530 5.19 520 5.10 530 5.19 527 5.16 80 590 5.78 580 5.68 600 5.88 590 5.78 100 650 6.37 650 6.37 640 6.27 647 6.34 Force needed to break cling film when the width of the cling film is changing. Width/mm Test 1/kg(x10-3) F=Ma/N Test 2/kg(x10-3) F=Ma/N Test 3/kg(x10-3) F=Ma/ N Average/kg(x10-3) Average F=Ma / N 10 110 1.08 120 1.18 110 1.08 113 1.11 20 230 2.25 230 2.25 220 2.16 227 2.22 30 440 4.31 450 4.41 450 4.41 447 4.38 40 640 6.27 630 6.17 640 6.27 637 6.24 Also with the aid of the equation: Force/N Cross-sectional area/m² =stress N/m² I also found out how much stress the cling film was under before it broke and knowing that the cling film was 1x10ˉ³ x 40 x 10ˉ³metres in cross-sectional area for the length experiments and for the width experiments dimensions of the cling film was 100x10ˉ³ metres by (n) mm (where n is the number of millimeters in the width). I obtained a new set of results. Length stress results Length/mm F=Ma/N Stress/N/m²(x103) F=Ma/N Stress/N/m²(x103) F=Ma/N Stress/N/m2(x103) Average/g Average stress/ N/m²(x103) 20 3.82 95.5 3.72 93 3.72 93 3.75 93.8 40 4.31 107.75 4.41 110.25 4.31 107.75 4.34 108.5 60 5.19 129.75 5.10 127.5 5.19 129.75 5.16 129 80 5.78 144.5 5.68 142 5.88 147 5.78 144.5 100 6.37 159.25 6.37 159.25 6.27 156.75 6.34 158.5 Width stress results: Width/mm F=Ma/N Stress/N/m² F=Ma/N Stress/N/m² F=Ma/N Stress/N/m2 Average/g Average stress/ N/m² 10 1.08 108 1.18 118 1.08 108 1.11 111 20 2.25 112.5 2.25 112.5 2.16 108 2.22 111 30 4.31 143.67 4.41 147 4.41 147 4.38 146 40 6.27 156.75 6.17 154.25 6.27 156.75 6.24 156 The results allowed me to plot a graph of the length and width of the cling film against the force at which it broke and the stress at which it broke. I have decided that the error bars in the graph should be + 0.5cm, so there will be a small chance of error in all my experiments. From the graphs it can be clearly seen that the width of the cling film has a great impact on the force that needs to break the cling film. It can also be seen that that the relationship between the width of the cling film and the force needed to break it is a directly proportional as the line goes through the points in a linear manner. With the length of cling film it is not that clear on the graph but the force does not have as much of an effect as the width does on the force needed to break the cling film. Whereas the length and the force needed to break the cling film has no relationship where the length of the cling film changes also. In addition, the stress for the length graph seems to stay around a range as the results for the width graph indicating a range where the real stress value may lie. With the aid of my results and the graph that if the width of the cling film increased by double then the force needing to break the cling film would also have doubled. The ranges for the length-stress graph were between The ranges for the width-stress graphs were between It may also be slightly inaccurate because of parallax error, as my view may have not resolved the points with the precise coordinates. The error bars for the force graphs were 980N (rounded to 1000N on the force graphs) downwards from the point, as the exact value would lie in between the force before the cling film would break and the force that caused the cling film to break. The error bars for stress, was estimated for the error bars for force. There is also the problem of the width constantly changing so I decided to use the median number in the equation, which is 6mm. The equation is as follows: Error in Force/N Cross sectional Area/m² = error in stress/N/m² Since I have already estimated that my error bar is 1 x1010 on the width-stress graph and length-stress graph this falls below the error in stress so my error bars are good for accuracy. From observation and analysis of my results and graphs you can see that the width line has a steeper line compared with the length line. These lines are shown to be positive because as the length and widths increase so does the force needed to break the piece of Clingfilm also increases. This is because as the cross sectional due to the fact that as The width line is steeper because it is affecting the cross sectional area, which means that the force needed to break the cling film, will increase as the cross-sectional area increases. The gradient of the length line is 0.035 and the gradient of the width line is 0.91. This shows that there is 0.035N of force per mm on the piece of Clingfilm for the length line and there is 0.91N of force per mm on the piece of Clingfilm for the width line Experiment 4: attraction between cling film and various surfaces: Aim: Testing to see how changing different surfaces that the cling film is attached to see the amount of force that is needed to detach the cling film from each surface. Finding out what surfaces cling film gets attached to best. Prediction: My prediction is that the cling film will attach to surfaces, which are the smoothest as I Apparatus: Ø Stopwatch Ø Ruler Ø Sets of 10g Masses Ø Boss clamp Ø Stand Ø Cling Film Ø Scissors Ø Stanley Knife Ø Clamps Ø Sticky tape Ø Vernier capular Diagram of Apparatus: Method: 1. The equipment will be set up on the bench. Using a Stanley knife I will cut a piece of cling film, which will be 50mm in length and 50mm in width. 2. I will place the cling film on to the material in which I will be testing its adhesiveness to. E.g. the wood, metal etc. 3. Then I will place some tape on the cling film. The tape will have a pieced hole in it which will be used to add the masses on. 4. Then I will add the masses on to the cling film until the cling film falls off 5. I will do this experiment three times to ensure accuracy. For this experiment using the formula force =ma (a=9.81NKg) I recorded the force required to separate the cling film from the surface to which it is adhered to. The surfaces I used were: acrylic, glass, metal and wood. My results are as follows: Results: Material that cling film is attached to Mass needed to detach cling film from surface /g1 2 3 Average Mass needed to detach clingfilm from surface /g Metal 360 355 365 360 Glass 140 150 145 145 Plastic 330 335 335 333 Wood - - - - What makes cling film stick to itself and other surfaces? As we know, when the cling film is pulled off the roll, it acquires electrostatic charge due to friction. This charge enables cling film to attract to other surfaces with the opposite charge. During this attraction the air between the two surfaces is pushed out, so a vacuum is formed. At this point, it is no longer the charge, which keeps the two surfaces joined together. When the vacuum ...