The hotter the metal becomes the more kinetic energy it gains and the metal ions begin to vibrate. As these ions vibrate they hit others around them and they start to vibrate as well. The heat gets passed along to cooler parts in the metal. So, the thicker the metal the longer the time it takes for the heat to escape, so this is why I think that the more layers of insulation the longer it will take to cool down.
How Varying the Start Temperature effects the rate of Cooling
I think that for this one the temperature will at first rise from 0ºc and 10ºC up until the start temperature is 20ºC, I think this because room temperature is 20ºC and they will rise to match that. I think the higher temperatures will cool more steeply. My scientific reasonings for this are to do with radiation. I know from text books that the higher the temperature the more heat radiation there is, so if the temperature is higher the more radiation is omitted and the quicker the water should cool. I think that all end temperatures after an hour will be around 20ºC (room temperature).
How a lid effects the rate of cooling
I think a lid will be similar to the layers of insulation, in that it will be harder for the heat to escape. With a lid the water can evaporate and it takes energy to evaporate, so when the energy is being used for evaporation the water can cool down. Having a lid should stop some of the evaporation, there fore keeping the water hotter for longer
How a fan effects the rate of cooling.
I think that a fan will quicken the rate of cooling quite a lot. This Is called forced convection. Convection is when hot water rises to the top of the container and cools then sinks where it is replaced by warmer water, this carries on in a circular motion until the water has reached room temperature.
AQA science revision guides
Class notes.
I also investigated Newton’s Law of Cooling for further understanding. This is it basically.
The relationship for the energy flow rate due to convective heat transfer at the boundary between a solid object and a fluid environment is referred to as Newton’s Law of Cooling. If we represent the surface temperature of the solid as Ţ and the bulk fluid temperature as Ŧ, then the energy transfer rate between the solid and fluid is Proportional to the surface area for heat transfer, A, and the temperature difference between the solid surface and the bulk fluid temperature. The proportionality constant is often given the symbol h, which is known as the heat transfer, coefficient.
Observations and Results
Control Experiment
Table of Results for Control Experiment
In this experiment the start temperature was 100ºC, room temp was at 20 ºC and 50mls of water were used.
How Layers of Insulation affects the rates of cooling
While I was conducting this experiment on the computer I could see a pattern emerging, the same way as I predicted. I said that as I added more layers of insulation the water would cool more slowly. Here is the table of results.
In this experiment the amount of water was 50mls and the start temperature was 100ºC, room temperature is 20º.
In this experiment I can see from a glance that the beaker with more layers of insulation is cooling slower than the control experiment with out any layers. I can see that the insulated experiments do not have enough time in the hour to fall right down to room temperature. Line of best fit =
How a fan affects the Rates of cooling
Controlled Conditions same as Insulation experiment.
Table of Results:
From this I can see the temperature dropping more steeply and cooling quicker with the fan as I predicted.
This graph show what I expected with the experiment without the fan higher up meaning that at the time points I measured the temperature was higher. See prediction for reasons why.
How does Varying Start Temperature affect the Rates of Cooling.
From the table I can see that the higher the start temperature the steeper the fall between the 10 minute gaps, for instance when the start temperature is 100ºC the drop between 10 and 20 minutes is 19.5ºC where as the gap between the same times when the start temperature is just 10º is just 2.3ºC.
Here is the graph of the same table.
How a Lid affects the Rate of cooling
I predicted that the lid would slow down the cooling process, because it would stop evaporation and some of the radiation. Here is the table of results:
Graph of Results
Analysis
After looking at the results once plotted in the graphs I can see there are a few anomalies. I am not sure why these are there but once re-trying the experiments on the computer they fitted into the line of best fit perfectly.
How Layers of Insulation affects the rates of cooling
In this experiment I have shown that with more layers of insulation the water takes longer to cool down, therefore I have proven my prediction when I said that, “The hotter the metal becomes the more kinetic energy it gains and the metal ions begin to vibrate. As these ions vibrate they hit others around them and they start to vibrate as well. The heat gets passed along to cooler parts in the metal. So, the thicker the metal the longer the time it takes for the heat to escape.” And from the graph I can see that with more layers of insulation, the temperature cools more slowly.
How Varying the Start Temperature affects the rate of Cooling
From looking at the graph and table of results I can see that, as I predicted, based on Newton’s Law, the higher the start temperature the quicker the water cools. There were quite a few anomalies in this, but the computer program is designed to include some anomalies so I put the mistakes down to this reason. This graph clearly demonstrates part of Newton’s Law of cooling, where it says about radiation and how the hotter the liquid the more radiation, so that water at 100ºC will cool at a rate quicker than water at 30ºC would. This was a successful experiment that I was pleased with the results of.
How a lid affects the Rate of Cooling.
As I mentioned in my prediction this experiment show how evaporation cools down liquids. When a substance evaporates it uses energy, there fore taking heat away form the rest of the liquid. So without a lid the water is able to escape, using energy, but with a lid, the water can’t. The lid also slows down radiation.
How a fan affects the rate of Cooling
So far, a fan has been the first of the experiments that has cooled the water quicker than the control experiment. This experiment displayed forced convection. (Convection – Transfer of energy caused by convection currents. These are set up when part of a gas or liquid is warmer than its surroundings [surroundings are cooled by the fan]. When warmer the gas or liquid is less dense. Source: AQA Science Revision Guide.) The reason it cooled the water quicker is explained in this diagram.
As I was doing the experiment with a lid (the only experiment I did for real) I spilt the water. This ruined the whole experiment, and I had to start again. In future I will have to be more careful, as it was a bit of a waste of time. It was also important for safety purposes, that I held the metal colorimeter at the top, and moved quickly so that the heat did not have time to be conducted and spread right the way to the top and burn my fingers. In future, it might be more sensible to use colorimeters that are rimmed with plastic.
To measure the temperature of the water we used a thermometer, to improve accuracy we could have used a digital temperature probe, these leave less room for human error. If we were to use a temperature probe, we could have plugged it into the computer and a graph could have been drawn automatically.
Evaluation
I thought my experiments all went well, and I got the results I predicted.
