Cotton wool - This is because it can be easily wrapped around the test tube and therefore cover most leaving fewer spaces for heat loss. Cotton wool is also the thickest material that is being tested, so that will keep in heat more as there is a lot of material between test tube and air. It also has a low density and traps air well like all good heat insulators such as duvets, loft insulating etc. This material is the closest to the sheep’s natural coat.
Foil - The foil should insulate heat quite well because it is used in cooking where it is wrapped around food that is going in an oven. Heat is reflected by foil and this should keep the water in the test tubes at a steady temperature.
Bubble wrap - I think the bubble wrap will be average at insulating heat because it is not very thick but it isn’t thin either. The trapped bubbles of air may act to insulate as the cotton wool.
Cotton - The cotton will be a very poor insulator of heat and I expect it to be one of those that lose the most heat because it is thin and lightweight as well as having small holes in the material, which will allow air carrying the heat to escape.
Paper towel - The paper towel is like the cotton in thickness and will not insulate the test tube very well and I believe that it will also be very poor therefore being one of those that lose the most heat.
Control - The naked test tube should lose the most heat as there is nothing covering it and therefore heat will escape quickly.
Method
- Collect apparatus.
- Measure 12cm by 12cm of each material and wrap 5 test tubes with material (different material for each test tube). Leave 1 test tube naked as a control.
- Do not cover the top or bottom of the test tubes.
- Hold the material on with elastic bands
- Carefully place the test tubes in a test tube rack.
- Pour some water into a kettle and boil.
- Once boiled measure out 10ml in a measuring cylinder and pour this amount into each test tube.
- Place a thermometer in each test tube.
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When the temperature of the water in each test tube is at 60°C start recording results.
- Record the temperature every minute for 20 minutes.
- Repeat until you have 3 sets of results for each material.
- Record results in a table.
- Plot a graph
Fair test
This experiment needs to be fair and consistent, in doing this I have used one variable (the material). I have measured the temperature and the things I have kept constant are the amount of water (10ml), the same amount of material around each test tube (12cm by 12cm), the starting temperature of the water (60°C) and the duration of experiment (20 minutes). I repeated the experiment three times for each material to ensure consistency and highlight any results that may be faulty, for example, the test tube may not be covered properly and therefore the set of results would not reflect fairly on the outcome. With 3 sets of results it is easy to see if something is wrong as you can easily compare the data.
Results
(Incorrect results not used – test tube not properly covered)
A graph of the average temperatures for each of the materials is shown on the next page.
Evaluation
The results I have recorded are considered to be very reliable as I made sure all factors in the experiment were kept the same to keep it fair and accurate. I have listed these factors in the fair test section earlier. There is, however, one set of anomalous results in the table that is highlighted red and I have not used them in working out the averages because I thought the eventual graph would not show the correct trend. That set of results are considered wrong because the bubble wrap that covered the test tube was not wrapped properly and only half covered, which allowed heat to escape quickly and therefore making those results void. I could have recorded more accurate temperature readings by using a data logger, which would give it at 2d.p as opposed to on the thermometer where you read the nearest degree. The results I have collected are enough to form a firm conclusion as I have tried five materials and I have done each material three times so that the results are accurate and to ensure the results are consistent. I could extend this experiment by using more materials such as leather, feathers, silk etc or I could also investigate using different layers of each material as well. This would enable me to determine the better heat insulator and find how much heat is lost through whichever material with any number of layers around the outside of the test tube. Alternatively we could use a specific weight of material rather than size. I could also leave the experiment for a bit longer to see a better pattern emerging. It might be good to leave it for any time between 30-60 minutes.
Conclusion
In conclusion my results show that cotton wool is the best heat insulator out of itself, bubble wrap, foil, cotton and paper towel. It only lost an average of 16.3°C over the 20 minutes and that was almost a full 3°C less than second best, which was the foil. The control test tube (naked) lost the most heat as it was left uncovered and the worst material was the paper towel but it held in on average 6°C more than the control test tube. These results are almost exactly as I predicted but the average amount of heat lost by each material is a lot closer to other materials than I expected. I have shown the averages below.
Cotton wool average lost – 16.3°C
Foil average lost – 19°C
Bubble wrap average lost – 20.5°C
Cotton average lost – 20.6°C
Paper towel average lost – 22.6°C
Control average lost – 28.6°C
