When it’s hot: -
- The hairs on the skin are lowered, brought about by the relaxing of erector muscles. As a result, the hairs lie flat, and a layer of air is no longer held between them, so heat is more easily lost.
- Blood flows closer to the surface of the skin, as the blood vessels near the surface widen so that more blood flows through them and the heat is lost through the skin. This is called vasodilation.
- Sweating occurs, and as the sweat evaporates, it cools the skin and the blood flowing near the surface. Evaporation occurs more quickly in dry air than humid air, and this is why we feel hot and sticky on a humid day. Movement of the air also helps evaporate the sweat, so this has a cooling effect.
- As an alternative to sweating, some animals pant, for example dogs. Dogs only have sweat glands on the pads of their paws, and they cool themselves mainly by panting. When a dog pants, water evaporates from their mouth and tongue.
All the responses listed above are involuntary and occur without us thinking about them. Other methods of keeping cool include putting on or taking off clothes, or moving to a shaded area. Both of these methods are deliberate steps to control our temperature.
The size of an animal also affects how heat is lost. A smaller body heats up and cools down faster, because they have a larger surface area to volume ratio. Bodies lose heat through the surface of the body i.e. larger surface areas result in greater gains and losses. The body retains heat from within itself, so a larger volume means more heat is kept in. When the surface area is large compared to the volume (e.g. mouse), heat is lost and gained quickly because there is only a small volume to keep the heat in. Larger bodies are basically the opposite, because they have a smaller surface area to volume ratio, for example an elephant has a large volume, and a large surface area, but when the surface area to volume ratios are compared, the mouse’s is bigger! The following example puts this simply:
Consider two cubes, both of exactly the same shape, but of different sizes. The smaller is 1m by 1m by 1m in size, and the larger is 2m by 2m by 2m in size. The smaller cube has a surface area of 6m² (area of one side times six – 1x1x6=6), and the larger cube has a surface area of 24m² (2x2x6=24). The smaller cube also has less volume (length x width x height = 1x1x1=1m³) than the larger cube (2x2x2=8m³). However, the smaller cube has twice the surface area to volume ratio (surface area divided by volume = 6/1=6) as the larger cube (24/8=3). Because of this the larger cube loses heat slower than the smaller cube because of the difference in this ratio.
I will be doing two separate experiments to simulate both insulation and surface area. The first will be using different types of insulation on beakers, all of the same size and volume. I will have three types of insulation - cotton wool, j-cloth, and a control test with no insulation. This experiment will test whether animals can retain temperature by means of having different types of layers to prevent heat loss. I will be using hot water to simulate the inside of the animal’s body, and measuring the temperature loss over a certain amount of time. The temperature will be lost by means of convection and radiation. Convection is the rising effect of water particles that have more energy moving to the surface, losing energy to the air, and the falling back to the bottom, and getting more energy, then rising again. Radiation is the loss of heat by passing energy on to the particle next to it, which in the beakers will pass through the glass of the beaker and then to the air around the beaker. Insulation is used in my experiment to slow down the affect of heat radiation.
In the second experiment, I will use three different sized beakers - a 75ml beaker, a 300ml beaker and a 500ml beaker, to simulate how smaller and larger animals lose heat at various rates. As before, hot water will be used to imitate the inside of the animal’s body, with heat being lost both by convection and radiation. I will work out the volume to surface areas beforehand so that I can predict which sized beakers will have the fastest or slowest loss of heat.
Prediction
I think that in the insulation experiment, the beaker with no insulation will lose heat fastest, followed by the beaker with j-cloth insulation, and slowest heat loss from the beaker with cotton wool insulation. This is because insulation should keep more heat in, and prevent heat being lost. I think the cotton wool will do this most efficiently, because it is a thicker material than j-cloth.
In the surface area experiment, I think the 75ml beaker will lose heat fastest, then the 300ml beaker, and slowest heat loss from the 500ml beaker. This is because the larger beakers will have smaller surface area to volume ratios resulting in slower heat loss.
Method
Both experiments must be kept fair by keeping all other variables, which will affect the speed of heat loss constant. One constant is the temperature around the beakers, which will be room temperature. Another is the humidity. This is difficult to control, but will however stay constant.
Experiment 1 – insulation
- Set up the equipment as shown below (without the water).
- Heat enough water in a kettle until boiled. Pour 300ml into each beaker, record the temperature of each beaker, and start the stop clock.
- Record the temperature of each beaker every 30 seconds for 10 minutes (600 seconds).
- After the 10 minutes are up, empty the beakers, and repeats steps two and three twice more, so you have three sets of results.
- Clear away equipment and evaluate results.
Experiment 2 – surface area
- Set up the equipment as shown below (without the water).
- Heat enough water in a kettle until boiled. Pour 75ml into the first beaker, 300ml into the second, and 500ml in the third. Record the temperature of each beaker, and start the stop clock.
- Record the temperatures every 30 seconds for 10 minutes (600 seconds).
- After the 10 minutes are up, empty the beakers, and repeat steps two and three twice more, so you have three sets of results.
- Clear away equipment and evaluate results.
Results
Insulation Experiment
Surface Area Experiment
Analysis
My results in the first experiment have shown that my prediction was correct. In the first graph, both the J-cloth and the cotton wool were effective in keeping heat energy in the beakers, as the graphs clearly show that they resulted in slower heat loss because the lines are both higher than that of the beaker with no insulation. The temperature of the beaker with no insulation fell rapidly at the start compared to the two with insulation, which both lost heat at a much slower rate.
I expected the cotton wool to give the slowest loss of heat, but the graph shows that at about 90 through the experiment, the j-cloth beaker had the highest temperature. This is probably because it was between the other two beakers, so was less exposed to the air than the other two beakers. However, in the end, it lost heat faster than the cotton wool covered beaker, and the results matched my prediction.
The general pattern is that all the beakers lose heat rapidly at first, but slow down as they reach the temperature of the air around them. Had the experiment gone on for longer, all three would eventually flatten out at room temperature.
These results prove that insulation lowers the speed of heat loss in animals, and more insulation makes the animal better at retaining heat.
Below are the calculations for the surface area to volume ratios for all three of the beakers I used.
Note:
d=diameter, h=height, r=radius
My results and calculations have shown a small surface area to volume ratio leads to a slower loss of heat in the same space of time as a large surface area to volume ratio. The 500ml beaker, with a ratio of 0.62 lost heat slowest of the three beakers. Although it had the largest surface area from which to lose heat, it also had a large volume in which to retain heat, so as the graph shows, it’s temperature cooled much slower than the other two beakers.
The 300ml beaker, with a ratio of 0.74 remained just below the temperature of the 500ml beaker throughout the experiment. This is also because of it’s low ratio.
The smallest beaker, with its high ratio, lost heat much faster than the other two beakers. This can be clearly seen at the start of the experiment, where the two larger beakers cooled fairly slowly, but the smallest dropped in temperature rapidly at the start, and kept dropping far below the other two. At the end of the experiment, it was nearly 10 degrees cooler than the other beakers.
The general trend of the graph begins with a sharp loss of heat, and then the lines become gentler as they reach room temperature. Had the experiment gone on for longer, all the lines would have levelled off at room temperature.
Evaluation
If I were to carry out this experiment again, I would extend the amount of time the temperatures are recorded to the amount of time it takes for each beaker to reach room temperature. This is because I would receive more conclusive results of which beakers had the fastest and slowest heat loss. To remove the result I got with the J-cloth, with it having a ‘peak’ at the start of the experiment, I would have each beaker at least 30cm away from each other, so no heat is transferred between the beakers. Another solution would be to carry out the experiment on each beaker separately, however this would be extremely time consuming.
I received anomalous results in the insulation experiment, which can clearly be seen on the graph. I expected that the beaker, which would maintain the highest temperature, would be the cotton wool, insulated beaker, but for most of the experiment the j-cloth insulated beaker had the highest temperature. By the end of the 10 minutes, the cotton wool did however have the highest temperature. The cotton wool showed the most predictable results of the two, with the most curving line, but the j-cloth gave more variable results, crossing the curve of the cotton wool beaker several times before finishing below it. This problem could be resolved by, as mentioned before, carrying out the experiment for each beaker separately.
To improve the accuracy of the experiment, I could record the temperature of each beaker more often, for example every 15 seconds instead of every 30 seconds. However, this would be quite tedious, as I found it difficult to keep up when the time was every 30 seconds! Another way to increase accuracy would be to measure out the amount of water needed first, and then pouring out the exact amount into the beakers, as the amounts poured in my experiments were only rough estimates, as the amount of heat lost if I had used this method would mean that my results all started at different temperatures.