So in my experiment, I’m changing the volume, (instead of the surface area), but I assume it will follow the same pattern as the cube diagrams. The results should plot out on a line graph like this:
The blue points represent the smaller volume (so the larger volume to surface area ratio), and the red points represent the larger volume (the smaller ratio). All the plotted points should connect as a reasonably straight line, and not a curve.
To receive such results, the experiment must be kept fair, meaning some variables must be kept constant. These are called the controlled variables, which include:
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the environment; the experiment should be done indoors with a normal room temperature of 22°C, not for instance outside where factors like wind, sun, temperature can affect the outcome.
- The starting temperature of the water should be the same with the start of each experiment.
- The size of the test tubes must be kept constant.
- The thermometer should reset to room temperature before each experiment.
All these must be kept constant as there can only be one tested variable at a time which can be changed (the dependant variable), otherwise the results will be based on more than one changed factor which won’t match up to the hypothesis of the experiment and will produce unreliable results.
Trial Experiment:
Prior to planning this experiment, a similar experiment was trialled to check if there were any defects, or to see if any changes could be made to improve the experiment. In this experiment, the volume was being kept constant while the surface area was being changed (the size of the test tube). The test tubes need to have their surface area calculated to work out the ratio, so here’s a brief overview of that:
Calculating the Surface Area:
To calculate the surface area of the test tube size used in the experiment, separate it into two calculations; the cylinder part and the half-sphere at the end.
Part A Part B
S.A= 2 x π x r x length S.A= 2 x π x r 2
S.A= 2 x π x 1.25 x 14 S.A= 2 x π x 1.5 2
S.A= 109.96cm (2 d.p) S.A= 14.14cm (2 d.p)
Above is an example of the large test tube calculations. ‘r’ represents the radius (half the diameter) and ‘x’ represents the times symbol. I won’t show the working out for all the sizes.
For this experiment not only was the independent variable different, but the starting water temperature was different too, being set at 45°C.
Results for trial experiment:
Even though the results follow my hypothesis, I decided that only having three different sized test tubes limited my results greatly. That’s why I changed the surface area to the independent variable (using the large test tube), instead of the dependant variable. Also, having the water bath set at 45°C, the water was quite hot and out of a comfortable temperature zone to handle with. For the next experiment I adjusted it down to 40°C, as this is a more suitable temperature.
Apparatus:
- 5x test tubes of equal size
- Test tube stand
- 30ml syringe
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Water bath, set at 40°C
- Thermometer
- Stopwatch
Diagram:
Method:
- From the water-bath, pour out 25mls into a test tube and place the thermometer in it.
- Remember- hot water is being dealt with so take care not to burn yourself or anyone around the experiment!
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Wait till the thermometer has reached a steady measurement and record the temperature: this should be 40°C.
- Start the stopwatch and record the new temperature for every minute for 5 minutes.
- Repeat steps 1-4 for test tubes of water with volumes of 20mls, 15mls, 10mls and 5mls.
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Repeat the entire experiment, steps 1-5, a further 2 times. This allows the results to be more reliable as an average can be drawn from the varied results; making sure they are within a close range.
Results
Heat-Loss Rate Experiments 1, 2, 3
& Averages
Line Graph on Heat-Loss Rate
Due to different Volume to Surface Area Ratios
Conclusion
My results and graph agree on my predictions, with a smaller volume to surface area ratio, there will be a slower heat-loss rate, (in this experiment, when there is a larger volume there is a smaller volume to surface area ratio). Apart from all descending at lower temperatures with smaller volumes, I can’t pick up any other patterns.
For the results I did receive, I can explain how these occurred using a similar theory to the cube diagrams, except I’m using test-tube shapes and changing the volume.
S.A= [ 2 x π x r x length ] + [ 2 x π x r 2 ]
S.A= [ 2 x π x 1.25 x 14 ] + [ 2 x π x 1.5 2 ]
S.A= [ 109.96cm ] + [ 14.14cm ]
S.A= 124.1cm
V= 25mls (25cm)
The volume to surface area ratio for this test tube is 25 : 124.1.
25 : 124.1
Divided by 25 Divided by 25
1 : 4.96
So, in a test tube with a surface area of 124.1cm and volume of 25mls, it can be simplified down to for every 1cm of volume, there is 4.96cm of surface area to lose heat from.
S.A= [ 2 x π x r x length ] + [ 2 x π x r 2 ]
S.A= [ 2 x π x 1.25 x 14 ] + [ 2 x π x 1.5 2 ]
S.A= [ 109.96cm ] + [ 14.14cm ]
S.A= 124.1cm
V= 15mls (15cm)
The volume to surface area ratio for this test tube is 15 : 124.1.
15 : 124.1
Divided by 15 Divided by 15
1 : 8.27
So, in a test tube with a surface area of 124.1cm and volume of 15mls, it can be simplified down to for every 1cm of volume, there is 8.27cm of surface area to lose heat from.
The first diagram has a smaller ratio, which means for every 1cm of volume there is less surface area to lose heat from.
Evaluation
Although the results are along the lines as I predicted, the plotted points on the graph aren’t as perfect as I thought they’d be. I’ve drawn lines of best fits through the points, so that they all have a smooth curve, but all of them have anomalous results, which I’ve circled. These random results suggest that some controlled variables weren’t kept constant.
Some factors that could have changed during the experiment and altered my results include:
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the environment; the experiment should be done indoors with a normal room temperature of 22°C, not for instance outside where factors like wind, sun-temperature can affect the outcome.
- The starting temperature of the water should be the same with the start of each experiment.
- The size of the test tubes must be kept constant.
- The thermometer should reset to room temperature before each experiment.
All of these must be carefully controlled to be kept constant. Some ideas to help me keep those most accurate include:
- The experiment could be done within room-temperature water, in shadow. So after adding the hot water to the test tube with the thermometer inside, that can then be placed in cooler room temperature water so that now you are more accurately controlling the surrounding temperatures.
- The test tubes could have also been kept in the water bath so that they didn’t influence the heat-loss rate of the volume of water added. (If the volume added was smaller then the ‘coldness’ of the test tube would influence it’s rate quicker)
- A new thermometer could be used each time, (along with new test tubes for each experiment).
Another defect in the experiment is that the test tubes are ‘open’, which allows heat loss through the constant flow of air, and not only through the glass (which is acting like the penguin’s ‘skin’). A way to prevent this is to get rubber test tube stoppers, with thermometer access. It resembles this:
Also when I am averaging my results, I should check to see that they are in a close range. E.g. within the 3 experiments, if I get timings of 13 seconds, 12.5 seconds, and 16 seconds, I should automatically decide that 16 seconds isn’t really within a close range with 13 and 12.5 seconds, and that I can get rid of that result and repeat that part of the experiment until I get results within a close/tight range.
Also, seeing as this experiment is within the classroom with some groups doing the exact same experiment, it’d be a good idea to compare the results I received to the other groups. This would allow me to see wether I’m on the right track and getting similar results or not.
Bibliography
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Williams, Tony D. "Penguin." Microsoft® Student 2006 [CD]. Redmond, WA: Microsoft Corporation, 2005.
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Ward, Paul. “Science of the Cold.” Cool Antarctica. [2001]
