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Investigation of Surface Area : Volume Ratio and its effect on Body Temperature

Introduction, Aims and Predictions

            There are many factors that determine how quickly or slowly heat is lost. Some of the factors are as follows: amount of water, shape, temperature and surface area to volume ratio. The aim of this investigation is to examine how variations in surface and volume ratios in organisms lead to variations in heat loss or retention. In theory a larger object should lose heat more slowly than a smaller object will as the larger object has a lower surface area to volume ratio than the small one so the heat will have further to travel. The theory that the larger the object the better it retains heat can be observed in certain animals. One example is the emperor penguin and the fairy penguin. The emperor lives in Antarctica and is large and the Fairy lives in Australia and is small. As the emperor lives in a cold climate it needs to retain heat. This is achieved because the emperor has a low surface area : volume ratio which means it retains heat more efficiently. The fairy needs to lose heat as it lives in a hot climate. It achieves this by having a high surface area : volume ratio which means it loses heat more  efficiently. Another example is the robin. In the winter the robin fluffs up into a spherical shape to give itself a smaller ratio so it retains heat more efficiently. In the summer it makes its body sleek and thin, giving itself a larger ratio so it loses heat more easily. Generally animals that live in cold regions tend to be bigger than those that live in hot areas because they need to retain heat. In this experiment beakers were used, as it would be unethical to use animals.

In this investigation a 100 ml flask and a 500 ml flask will be used. Their surface area to volume ratio can worked out by dividing surface area by volume. The following calculations give the ratio for each:

a)   100 ml flask - 115/100 = 1.15:1

b)   500 ml flask - 330/500 = 0.66:1

I predict that the 100 ml flask will lose heat 2 times quicker than the 500 ml flask as the 500 ml one has roughly half the surface area: volume ratio of the 100 ml one. For example if the 100 ml flask loses 1 degree centigrade per minute, the 500 ml one will lose half a degree centigrade per minute.

            A preliminary experiment will be carried out. It will basically be a trial run of the main experiment and the purpose of it is to check that equipment and timings are appropriate. It was also decided that at some stage there should be a separate experiment in which the beakers are wrapped in bubble wrap to imitate an animal. I predict that the beakers will lose heat more slowly when they have bubble wrap on because it will help retain heat.

Apparatus

2x Clamp Stands

2x Beaker with thermometer

1x Water Heater

            In the preliminary experiment a 500 ml beaker was filled with hot water and left in a water heater until the temperature was as near to 75 degrees centigrade as possible. 75 degrees is used because it is quite high above room temperature. The apparatus was then set up as in the diagram and the temperature in degrees centigrade was then taken every 10 minutes using the thermometer attached to the flask.  The results were then noted. The aim of the preliminary experiment was to assess whether or not the experiment was suitable or not. After the preliminary experiment had been performed it was decided that a couple of things needed to be changed to make the experiment more suitable. For a start to make the test fair the recordings should be of two beakers of the same size at the same time rather than just one as

more constant results will be achieved. Secondly the recordings should be taken every minute as opposed to every 10 minutes as more accurate results will be achieved and there is not enough time to measure the temperature every 10 minutes. Also the variable factors need to be considered in order to make the test a fair one. If the variables are not the same in both the

beakers inaccurate results will be achieved. For starters the temperature of the air needs to be considered. Also the colour of the flask needs to be considered (a black flask will absorb heat). The metal clamp needs a rubber coating round it otherwise the metal will conduct heat thus giving inaccurate results. The depth of the thermometer needs to be the same in both beakers. Another thing to consider is that the beaker is not so low on the clamp stand that it touches the wooden bench otherwise the wood will absorb some of the heat. The temperature and amount of the water in the beakers before the experiment starts needs to be the same in each experiment. Finally the beakers all need to be the same height on the clamp stand .To make the test a safe one the beaker should be reasonably low down on the clamp stand.

            It was decided that there should be three separate experiments. The first will comprise of the temperature of two 500 ml beakers being taken every minute for 15 minutes overall.

This will give more constant results, as the variables (e.g. room temperature) will be the same. The one downside to this however is that there won't be a direct comparison between the 500 and 100 ml beakers. The second experiment is the same as the first but with two 100 ml flasks. The third uses one 500 and one 100 ml flask. Both are wrapped in bubble wrap in order to imitate an animal (the bubble wrap is the equivalent of fur or another such protective coating). The method will be the same as in the preliminary experiment however as aforementioned the temperature will be taken every 1 minute for 15 minutes as opposed to every 10 minutes.

Experiment 1 (500 Ml Flasks): The results have been averaged

Experiment 2 (100 Ml Flasks): The results have been averaged

Experiment 3 (100 ml and 500 ml flasks in bubble wrap)

100 Ml Flask

500 Ml Flask

Heat Loss per Minute Calculations

Formula = temp at 0 mins - temp at 15 mins divided by 15

1)    100 ml : 72- 57/15 ą 1 degree per minute

2)   500 ml :74-66.5/15 ą 0.5 degrees per minute

3) 100 ml (in bubble wrap): 72-64.5/15 ą 0.5 degrees per minute

4) 500 ml (in bubble wrap): 74 - 70.25/15 ą 0.25 degrees per minute

Analysis and Conclusions

          In my predictions I stated that the 100 ml flask would lose heat 2 times more quickly than the 500 ml flask. The results to my heat loss per minute calculations back up this prediction as the heat loss per minute of the 100 ml flask was 1 degree centigrade whereas the heat loss per minute of the 500 ml beaker was 0.5 degrees centigrade. I also predicted that when bubble wrap was placed on the beakers they would lose heat more slowly than when they didn't have bubble wrap on. This prediction is supported by looking at the graphs entitled "100 ml flasks" and "500 ml flasks". By looking at the heat loss per minute results for the insulated beakers, we can see that the beakers lose heat at half the speed they did when they were non-insulated. For example the 100 ml beaker lost 1 degree centigrade per minute without bubble wrap. When it had bubble wrap on it lost heat at 0.5 degrees centigrade per minute.

            In conclusion, the speed at which an object loses or retains heat at is directly proportional to it's surface area : volume ratio. If the object is insulated it will lose heat more slowly than it would if non-insulated.

Evaluations

            The evidence I obtained was sufficient to corroborate my predictions. As the results were averaged and all variables were considered there were not really any anomalous results. However one error that was made was that the start off temperature for the 100 ml beakers was 72 degrees whereas the start off for the 500 ml beakers was 74 degrees. This error occurred because the timing of the 100 ml test tubes began too long after the beaker had been removed from the water heater. My results were very reliable as all variables were considered and the temperature readings were taken every minute exactly. I would make the following improvements on the experiment: 1) Set up two 500 ml beakers and two 100 ml beakers at the same time.  In my experiments two 500 ml beakers were done one day and the next day two 100 ml beakers were done. This meant that a direct comparison was not achieved as the room temperature on the first day differed from that of the second day.

2) Use apparatus that measures water with more precision. The beakers that we used did not have very accurate markings on and so it was possible that we put too much or too little water in.

3)   Heat the 100 ml beakers above 75 degrees as they loses heat quite rapidly and so the start off temperature will not be 75 degrees unless you heat the water to a higher temperature.

If I was going to investigate further I would try different sized beakers. I would also investigate other factors  that affect heat loss such as shape of object. I would also investigate how different air temperatures cause differentiation in heat loss. 

References

          Thanks go to the following for supplying information:

1)    Life Story by F.M Sullivan

2)   BBC wildlife on one

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