Results
Method
Firstly, place two tubes in a test tube rack and label one wet and the other dry. Then, boil 100ml of water using a kettle. When the kettle has boiled pour all of it into a beaker. Then using two measuring jugs, measure 31ml of water into each of them. Place a thermometer in each jug. When the temperature reaches 65°c, place one towel into the remaining water in the measuring jug. At the same time, wrap the test tube marked dry with a dry tissue and wrap the test tube marked wet with the wet tissue. Pour the water from one jug into a test tube and at the same time pour the water from the other jug into the other test tube. Immediately after, place a cork into each test tube and start the timer. Place a thermometer through each hole in the corks. Using a magnifying glass, take the reading of the temperature every 30 secs for 10 minutes.
Fair Test
In the experiment, I will keep the starting temperature, the amount of water, the type of tubes, the thermometers, the magnifying glass, the material of the towel and the bungs the same throughout the experiment The only thing I will be changing will be whether the towel is wet or dry. I will keep everything else the same throughout the experiment so that I can obtain reliable results. If I don’t keep the starting temperature the same, then in one of the experiments there will be a larger gradient for the water to cool down in and so this will make my results void. If I don’t keep the amount of water in each tube the same then in one experiment the cooling down process will be longer than the other and will also make my results void. If I don’t keep the size of the test tubes the same then in one experiment there may be more surface area of water exposed than in another, so one of the experiments will cool down faster then the other. This would make my results void. If I don’t keep the material of the bungs the same, then in one experiment I may have a rubber bung and in a different experiment I may have a cork. The rubber bung is a much better insulator and so this will let less heat out than the cork. This will make my results void. If I use a mercury thermometer in one experiment and a digital thermometer in another, then I will have more accurate results in the experiment with the digital thermometer. This will make my results void. If I use an 8x magnifying glass in one experiment and a 10x magnifying glass in another experiment then the experiment with the 10x magnifying glass will have more accurate results because it will display the temperature more clearly. This will make my results void. If I use a paper towel in one experiment and a cotton towel in a different experiment then the experiment with the cotton towel will cool slower than the experiment with the paper towel. This will make my results void.
Safety
To ensure no injuries while performing the experiment, wear safety goggles at all times due to glassware. Consult the teacher if there is a breakage. Also be careful while handling hot water as it may scald and also take EXTREME care while handling any mercury thermometer. In the event of it breaking, tell the teacher immediately due to mercury being Radioactive.
Prediction
I predict that the test tube wrapped in a wet towel will lose heat quicker than the test tube wrapped in a dry towel. I think this because when we sweat, our sweat will be the same temperature of our body. Our body uses heat energy to evaporate the sweat. The capillaries dilate to increase blood flow and heat is lost. Aswell as sweating, the body hairs lie flat so that heat can escape. The sweat gives a cooling effect to the skin. In the experiment a similar principle will occur. The test tube with a wet towel will lose heat quicker because the heat energy from the hot water in the test tube is evaporating the water from the towel. This is like the heat energy of the body evaporating the sweat. The tubes will not lose heat at the same rate due to different gradients. The tube with the wet towel wrapped around it will lose heat at a quicker rate at the beginning of the experiment because of the evaporating effect taking place immediately while at a high gradient. The heat will be transferred through radiation because the heat energy from the water will be absorbed by the wet towel. I predict that my graph for the dry towel will look like this. At the beginning, the temperature decreases steadily and towards the end of the graph the temperature decreases at a much smaller gradient and this causes the curve to flatten at the end.
I predict that my graph for the wet towel will look like this. At the beginning, the temperature decreases quickly and towards the end of the graph the temperature decreases at a smaller gradient and this causes the curve to flatten towards the end.
When I put both of my predicted curves onto the same graph it looks like this. It is clear that the experiment with the wet towel cools down quicker than the experiment with the dry towel.
Analysis/Conclusion
From my graph, I can see that the tube wrapped with the wet towel cooled down quicker than the tube wrapped with the dry towel. Both of them do not cool at a constant rate. In first few minutes, both of the tubes cool down faster but towards the end the rate at which they cool down is getting slower. This is due to there being a big gradient at the beginning of the experiment and towards the end there is a smaller gradient. This big gradient at the beginning will cause the graph to shoot down at a high gradient and towards the end of the graph will flatten out due to the lower gradient. My results do match my prediction because as I said in my prediction, the tube wrapped in the wet towel would cool down quicker than the tube wrapped in the dry towel and this is evident in my results.
Evaluation
When I took the readings of the temperature, occasionally I misread the reading and retook it immediately. If I did the experiment again, I would read the temperature correctly the first time and therefore obtain better results. Also when I looked at the stopwatch every 30 secs, I sometimes took a reading too early or too late. This did not reflect on my results because my graph had a smooth curve, but to avoid doing this again, I would have one person reading the timer and another person getting ready to take the reading. By doing this, I would be working more efficiently. I have one anomalous result on my experiment. On the graph showing a dry body, the very last result which was taken at 600 secs is anomalous. This is due to either taking the reading too late therefore letting the water to cool down more than it is allowed to. Or it is due a fault when taking the reading e.g. taking the reading at a much lower reading than it actually is. I could prove that this is an anomalous result by repeating the experiment. If I did this then there would be no anomalous results because I would be more accurate when taking readings and timing.
Critically Evaluate Evidence
A better way to have done it would have been to concentrate on the accuracy of timing and results. If I were to do my experiment again I would alter the frequency of results. This would also give the same conclusion.
