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:The effect of size and shape of a warm blooded animal on how quickly it losses heat.
Aim
The aim of this investigation is to find the effect of size on temperature
loss in warm-blooded animals. I am going to investigate the relationship
between objects and the rate at which they loose heat. We will be using
beakers as containers to represent animals in this investigation.
Introduction
Warm-blooded animals have the ability to achieve homeostasis. One of the
properties of homeostasis is the maintenance of a constant temperature
irrespective of their environment. Cold-blooded animals on the other hand
maintain their body temperature by behavioural means. An example is a
cold-blooded creature going out to bask in the sun and taking shade when the
creature is too hot. Therefore warm-blooded animals have certain advantages
over cold-blooded animals: -
§ They can remain active all day.
§ They can survive in harsh environment.
The advantage of warm-blooded animals is that all these internal processes
that maintain the body temperature require a lot of energy. This energy is
obtained from food. Warm-blooded animals eat up to ten times as much as
cold-blooded animals because their demands are greater.
Due to the reasons mentioned above, it is vital that warm-blooded animals
reduce heat loss. This can be achieved by;
§ Having the right size and shape
§ Physical means -
§ Insulation (hair trapping air & layers of fat)
§ Vasodilatation / vasoconstriction
§ Sweat production
§ Behavioural methods-
· Hibernating
· Increased movement
· Burrowing
· Seeking shade
· Wallowing
· Basking
As I recently found out, as the size increases the volume increases. The
larger the surface area/volume ratio the larger the heat loss. This is
because the molecules have less distance to travel and more surface area to
lose heat to.
Because of this, small organisms lose heat faster than larger one's. There
is also a relationship between the shape and surface area/volume ratio.
Evidence of this can be found in nature as Bergmanns rule suggests. Polar
bears are the largest bears on earth and live in the colder regions,
therefore they greatly reduce their heat loss. Tropical bears are the
smallest on earth and live in the hottest region therefore they have a
larger rate of heat loss so they don't over-heat.
Planning
I will try and ensure a fair test.
The apparatus I will be using are:
· 4 beakers of similar shape but different size. 75cm , 200cm ,500cm ,
1500cm .
· Thermometers
· Stop watch
· Water
· Water heater- one that keeps a constant temperature.
Measurements
I am going to measure the temperature loss. This means I will measure the
decrease in temperature by the minute for a reasonable length of time.
Variables
· Size of 4 containers.
· Insulation.
· Control
I am going to control;
§ Shape of liquid- by using the right measuring instrument to measure the
level of the liquids in each beaker.
§ Type of liquid- by taking water from the same source
§ Room temperature- must be recorded throughout experiment
§ Time interval- I have chosen 10 minutes for the length of my experiment
because it is a reasonable length and we will be able to gather reasonable
results
§ The starting temperature- I chose to start each experiment at 50 degrees
Celsius. I chose to start at this temperature because it doesn't require
much heating and therefore time isn't wasted.
All these are being controlled because I want to ensure that the
investigation is fair.
Prediction
I predict that the smaller containers will lose heat more quickly than the
bigger containers. Size has a relation to the surface area/volume ratio,
which also has a relation to heat loss. It can be proved that small objects
have a larger ratio and therefore lose heat quicker.
High ratios mean higher rate of heat loss because with a large surface area
and a low volume the water molecules have less distance to travel and more
surface area to lose heat on. We can say otherwise for objects with low
ratios.
EQUATION for surface area/volume ratio: 2 (r + h)
rh
These ratios help us predict the rate of heat loss. I found the SA/V ratio
for each one of the cylinders I am going to use. By obtaining the SA/V
ratios I can use the ratios in relation to each of the beakers so that I can
tell if one beaker, for example has half the ratio of another beaker and I
can predict the ratios of heat loss in the same way.
1. 75ml = 2 x ( 2.5 + 4.4 )
2.5 x 4.4
Therefore, SA/V ratio = 1.25
2. 200ml = 2 x ( 3.75 + 6.4 )
3.75 x 6.4
Therefore, SA/V ratio = 0.846
3. 500ml = 2 x ( 5 + 8.45 )
5 x 8.45
Therefore, SA/V ratio = 0.637
4. 1500ml = 2 x ( 7 + 17.3 )
7 x 17.3
Therefore, SA/V ratio = 0.401
From the ratios I predict that:
1. The 75ml container will have a heat loss approximately twice as fast as
the 500ml container's rate of heat loss.
2. The 200ml container will have a heat loss approximately twice as fast as
the 1500ml container.
3. The 500ml container will have a rate of heat loss approximately half as
slow as the 75ml container.
4. The 1500ml container will have a heat loss approximately thrice as slow
as the 75ml container.
Prediction (experiment with lid)
The addition of a lid will reduce the rate of heat lost. The reason for this
is that heat is lost in 4 main ways in this experiment, evaporation,
conduction, convection, and radiation. By adding a lid I am cutting out
evaporation because the hot air can't escape, and I am cutting out
convection because there are no currents of air taking away the hot air.
I predict that the rate of heat loss will be reduced by half because half of
the ways of heat loss have been neutralised by the adding of a lid.
Apparatus
· 4 beakers of similar shape but different volumes.
· Stop watch.
· Water heater.
· Thermometer.
· Polystyrene- used as a lid
Diagram
Method
Safety precautions
§ Making sure the start temperature wasn't too hot so that if an accident
occurred the chances of burning would have been reduced considerably.
§ Using a water bath rather than heating beakers. This reduces risk of
burning and ensures a constant room temperature.
§ Utilising a big space to prevent accidents. This was done by pairing
students up to perform the experiment.
Stages of experiment
§ I collected the apparatus
§ I heated some water in a water bath
§ I poured some water into the first container.
§ When the water was at the correct volume I let it cool down to the start
temperature of 50 degrees Celsius.
§ With the thermometer in the container I measured the temperature.
§ With the stop clock I measured the temperature every minute for10 minutes.
§ I did the same for my 3 other containers.
§ I repeated the experiment to gain more accurate results.
§ When I changed the variable, I repeated this experiment again and did a
repeat but this time I had a polystyrene insulation.
How I made this a fair experiment
§ I controlled the volume of the liquid using accurate measuring instruments
§ I controlled the shape of the liquid by using containers of similar shape
§ I chose containers made of glass from the same company; therefore the
composition of glass would be controlled.
§ I carried out the experiment in about an hour ensuring the outside
temperature was the same
§ I controlled the type of liquid by taking all the water from the same
source.
§ I made this a Fair experiment by repeating the experiment. This made the
experiment fair because if my results were consistent then my results must
be accurate.
Problems I had
§ Getting the start temp for all the beakers to be 50 Celsius
§ Avoiding an accident
§ The table conducted heat
§ Making sure no water was lost
Results
First experiment
Minute(s)
1 2 3 4 5 6 7 8 9 10
Volume of container (cm)
1500 50 50 50 50
49 49 48.5 48.5 48 48
500
50 48.5 48 48 47 47 45.5 45 44 43
200
50 45 44 43 42.5 42 41 40 38 37.5
75 50 46 44 42.5 40 38 37 35 33 31
1500 50 50 50 49
49 49 49 48 48 47.5
500
50 49 48 47.5 47 47 46 45 44.5 44
200
50 47 46 45 43.5 42.5 41 39 38 37
75 50 46.5 45 43 40 38 36.5 34 33 31
Room temperature- 25 degrees Celsius
Experiment with polystyrene lid
Minutes
1 2 3 4 5 6 7 8 9 10
Vol. of container (cm )
1500 50 50 50 50 50 50 50 50 50 49.5
500 50 50 50 50 49.5 49.5 48
48 47 46
200 50 50 50 49.5 49.5 49 48
47 46 45
75 50 49 49 48.5 48 47.5
46 45 44 43.5
Conclusion
When I compare my results to my prediction I find that my results have
successfully support my prediction. The results clearly state that the
beakers with the highest SA/V ratio lose heat at a higher rate than the
beakers of a lower SA/V. the results of the experiments involving a lid have
the result of decreasing the rate of heat loss. My original prediction
that
objects with higher SA/V ratios will lose heat at a higher rate than objects
with a lower SA/V ratio has been supported in both experiments.
In the experiment involving a lid the results are more consistent and have
provoked patterns. As stated before the higher the SA/V ratio the higher the
rate of heat lose, but I have I have also noticed that in the experiment
involving a lid, the results show a distance between finishing temperatures
increases. The results from the experiment that did not include a lid don't
have this constantly increasing distance between temperatures.
I made the prediction that the result of the experiments would roughly
follow in the pattern of the ratios that I derived in my prediction.
BEAKER 75ml 200ml 500ml 1500ml
Exp. with lid 8.5 5 4 2
Exp. without lid 18 12.5 7 4
My results don't follow the exact pattern of my predicted ratio, however the
results do follow the pattern of increasing heat loss as the SA/V ratio
increases. The results show that the lid does decrease the rate of heat
loss. These results shown above can be applied to the other predictions I
made.
The 75ml container will have a heat loss approximately twice as fast as the
500ml container's rate of heat loss.
75ml 500ml
Exp. with lid 8.5 4
Exp. without lid 18 7
This prediction has more or less been supported by the experiment with a
lid, but undermined by the experiment without a lid.
The 200ml container will have a heat loss approximately twice as fast as the
1500ml container.
200ml 1500ml
Exp. with lid 5 2
Exp. without lid 12.5 4
Again this prediction has been supported by the experiment with a lid, but
undermined by the experiment without a lid.
The 500ml container will have a rate of heat loss approximately half as slow
as the 75ml container.
75ml 500ml
Exp. with lid 8.5 2
Exp. without lid 18 4
Again the experiment with the lid has supported my prediction, so has the
experiment without the lid.
The 1500ml container will have a heat loss approximately thrice as slow as
the 75ml container.
75ml 1500ml
Exp. with lid 8.5 2
Exp. without lid 18 4
My prediction hasn't quite been supported by both experiments.
In all cases there is no corresponding result that can support my final
prediction. It seems that the results from my experiment using a lid are
more useful to support predictions than the experiment without a lid. The
graphs of the experiment show smooth curves and also very strait curves.
This is due to the varying rate of heat loss in some cases. The straighter
curves are of the results from the beakers, which had a relatively low SA/V
ratio, the more curved the graphs became. Each curve appeared to flatten off
as time went on. It is therefore possible to say the rate of heat loss
decreases with time.
The effects of having the lid is that the results obtained are easier to
work with. The results obtained from the experiment involving a lid are more
consistent in the sense that there are few points, which are close to the
line of best fit when compared to the experiment without a lid. I think that
this is as a result of two things. Firstly because convection and
evaporation have been cut out, there is less heat loss. Secondly, because
these forms of heat loss don't apply, the heat loss is concentrated and
would be constant. Evaporation can be an erratic form of heat loss because
there can be different strengths of air current depending on surrounding
air.
From my results I have discovered the percentage of heat loss that the lid
was able to cut out:
Errors
1. The bench was wet at times which would increase heat loss by conduction.
This is due to the fact that water has a high specific heat capacity
therefore has the ability to store large amounts of heat before increasing
it's own temperature. The water could have absorbed lots of heat from the
beaker because of this.
2. It was difficult to get the water at precisely 50 degrees Celsius each
time. The problem was because the water might have started to cool before
the timer had started.
3. The measurements may not have been accurate. This is possible at the
beginning of each experiment
4. An error that can be related to the experiment without a lid is that
there could have been strong wind currents, which were erratic in the
appearance. This could have meant that the experiment being carried out
could have been under different atmospheric conditions than that of another
due to the fact that evaporation was a very important and functional form of
heat loss.
5. The experiment was carried out over a number of days in which the outside
temperature and air pressure may have differed.
Improvements:
1. The experiment could have carried out in a room with mechanically
controlled temperature.
2. Having all experiments done in the same place at the same time.
3. I could have made sure the table on which the experiment was carried out
was cleaned of any foreign substances.
4. I could have prevented erratic air currents by enclose the place of
investigation.
Extensions:
1. I could introduce more beakers of different sizes.
2. I could use insulation around the entire beaker. This would cut out
conduction and some radiation.
3. I could have altered the shape of the containers and use different
materials, which inevitably will have different properties with regard to
heat loss.
Bibliography;
ü GCSE biology text book
ü GCSE physics text book
ü Biology notes
ü Britannica
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