Investigating Factors that Affect the Time It Takes for a Hot Beaker of Water to Cool Down

Investigating Factors that Affect the Time It Takes for a Hot Beaker of Water to Cool Down
To investigate the factors that effect the time it takes for a hot beaker of water to cool down. Heat is generally transferred by conduction, convection and radiation and evaporation. All of these processes can happen simultaneously but it is likely that one will give the greater heat exchange. Here is a description of the following processes that will affect my experiment: Evaporation === This could cool down the water, as when the water evaporates it will take the heat away with it in the same way evaporating sweat cools down our bodies. If I use a lid this could slow down the process. As the water vapour will not be able to escape into the air as quickly as it would normally, keeping the heat in for longer.
Conduction == This is where heat energy passes through the walls of the beaker by making the particles of the beaker vibrate and then they will make the particles next to them vibrate causing the heat to pass through the walls of the beaker and out to the surroundings. Materials that are good thermal conductors tend to be good electrical conductors; metals such as gold, silver and copper have a high thermal conductivity?s and will conduct heat readily. Materials such as glass have much smaller heat transfer values and are poor heat conductors. Convection == This is where the cooler water particles sink down to the bottom and the warmer water particles float up to the top. Convection will only affect my experiment if I do not have a lid. This is because the warm water will float up to the top and the heat energy will escape out of the top. If a beaker of water was being heated from below then the water particles at the bottom of the beaker will become warm and therefore become less dense, they will begin to rise to the top of the beaker. As the warmer water particles begin to rise, the cooler water particles at the top of the beaker will sink to the bottom, as they are less dense. Once at the bottom of the beaker they will start to get warmer and become less dense. This process will continue until the beaker of water is at the same temperature. Radiation ===== This is when the warm water particles vibrate the water particles next to them. This will give them more energy and will make the water there warmer. The water particles at the top of the beaker will radiate the heat energy into the surrounding air. For heat to radiate it does not need to be in contact with matter. Heat can radiate for something to another body through a complete vacuum, this is how the sun heats up the earth. This process can also be called the Wave Motion. Prediction As I decided to change the diameter of 5 beakers (with same amount of water in), I predict that if the diameter decreases the time taken for the hot water to cool will increase. This is because as the diameter of the beaker decreases the surface is therefore the only part of the object in contact with the environment. The majority of the heat will remain internal within an object whose surface is very small. The heat can only be conducted away through direct contact, and this area of the beaker is small. Also the area that heat loss could occur through convection and radiation is small. The surface like the surface for conduction for evaporation is also reduced. With all 4 factors reduced then the heat loss to the environment will be reduced, and the particles inside will have a great amount of Kinetic energy. Equipment: 5 different sized beakers Measuring cylinder Kettle Stopwatches Rulers Thermometers Safety goggles Variables and factors
Volume of water
If there was a lid
Temperature of water was the same
Temperature outside the beaker
Preliminary experiment We decided to do a preliminary experiment to test our equipment and methods. I decided to take the largest beaker and put into 200ml water into it at boiling. The water temperature lowered so rapidly that the starting temperature was 75C and we were initially going to start the experiment at 80C lowering to 70C and timing this 10C drop. We realised that this was not possible so we changed the starting temperature to 70C and we waited for it drop to 60C. I found that this was successful so I used this method for my actual experiment. What we did: We decided to investigate the factors the affect the time in which it wakes a hot beaker of water to cool down, from 70C to 60C, by changing the surface area of the beakers. We used 5 different beakers: 1- Diameter of beaker 7.5cm 2- Diameter of beaker 10cm 3- Diameter of beaker 11cm 4- Diameter of beaker 14cm 5- Diameter of beaker 16cm Fair test We made this experiment a fair test by:
Keeping the volume of water the same by using measuring cylinders.
Making sure we did all the experiments in the same conditions
Using only glass beakers
Doing the experiment at room temperature 27C
I decided to measure the time taken for the hot water to cool from 70C to 60C. This was done for all 5 beakers, repeated 3 times so that an average could be taken. Method In this experiment we will have 5 different beakers: 1. Diameter of beaker 7.5cm 2. Diameter of beaker 10cm 3. Diameter of beaker 11cm 4. Diameter of beaker 14cm 5. Diameter of beaker 16cm Put safety goggles on Collect all the equipment for the experiment Boil the kettle Pour 200ml into measuring cylinder and then into each beaker We then put the thermometers into the beakers, so we knew what the temperatures were Then we waited for each beaker to get to the temperature 70C where we then started the stopwatches We recorded the room temperature so that it was kept constant We timed how long it took for each beaker to get to 60C from 70C. After those were recorded we repeated it again 3 times We then plotted our results onto a graph Safety Safety precautions were needed because I was dealing with hot water, which can scald. The following things needed to be acknowledged to, in order to keep this experiment safe:
Be careful not to knock over the beakers with the hot water in
Be careful not to knock over other peoples beakers
Care is needed when pouring hot water
Do not run with the hot beakers
Wear safety goggles to protect our eyes
Tuck stools under the benches to prevent accidents
Keep the beakers far from the edge of the table
Results Experiment 1: Beaker 1- Time: 5.26 mins Beaker 2- Time: 3.58 mins Beaker 3- Time: 3.02 mins Beaker 4- Time: 1.49 mins Beaker 5- Time: 1.25 mins Experiment 2: Beaker 1- Time: 5.46 mins Beaker 2- Time: 4.36 mins Beaker 3- Time: 3.34 mins Beaker 4- Time: 2.04 mins Beaker 5- Time: 1.37 mins Experiment 3: Beaker 1- Time: 5.29 mins Beaker 2- Time: 4.07 mins Beaker 3- Time: 3.26 mins Beaker 4- Time: 1.54 mins Beaker 5- Time: 1.16 mins Beaker Diameter (cm) Results (secs) Average (secs) 1 2 3 1 7.5 326 346 329 333 2 10 238 276 247 253 3 11 182 214 206 200 4 14 109 124 114 115 5 16 85 97 76 86 Conclusion From looking at my graph and results table, I conclude that there is a change at the rate at which the heat transfers through the beaker. Altogether I tested 5 diameters and I have discovered which one has the quickest heat loss. I will place them in order of the fastest heat loss: Beaker 5 Beaker 4 Beaker 3 Beaker 2 Beaker 1 Looking at my predictions now, having done the whole experiment I have found myself to be right. This is due to the fact that I predicted that as the diameter increased the cooling time would decrease. My results show this, as they show that the cooling time increase?s when the diameter of the beaker is smaller. On my graph I can see a pattern of a downward sloping line as the diameter of the beaker gets smaller. This also proves my prediction was correct. From these statements I conclude that:
Heat loss is reduced when there is a smaller diameter
Evaporation, radiation, convection and conduction are major
factors of heat loss
Results could be faulty depending on the surroundings or
conditions; you have to have the same conditions/surroundings for
your experiment to be fair and accurate.
The bigger the diameter of the beaker the less time it takes for
the water to cool as there is a bigger area for the water
particles to escape.
Evaluation I feel that I was precise when measuring the volume of water and the temperature. I measured the water with a measuring cylinder and made sure it just touched the line. Also I measured the temperature with a thermometer to the nearest 0.5C. I measured the starting temperature accurately, and I also measured the time to the nearest second with a stop clock. These factors also helped to contribute towards a fair test. One of our biggest safety concerns was that the water was extremely hot and could have seriously burnt someone if we weren?t careful. So to prevent this from happening we made sure we had the kettle on our table and poured it carefully into the measuring cylinder over the sink. The person holding the measuring cylinder was also holding it with cloth as to prevent getting burnt. I thought I did take enough readings as I recorded 5 different beakers to give me a nice range. I also repeated the experiment 3 times and calculated the mean average. This means I had 3 different points for each 5 of the beakers used for the graph therefore it was much more accurate, so my graph was also good. I did obtain a few anomalous results. These results may have been in error because I may have moved the thermometer from the middle of the beaker slightly higher or lower or a little bit to the left or right. Another reason for the inaccurate results is that I may have started the stop clock too late after the thermometer got to 70C or too early. There was only one thing we could not really control and that was the temperature outside the beaker, the room temperature. We were unable to control this as we did 3 tests on one day and 2 on another. This means the room temperature on each of these different days could have affected our results. We didn?t have much time to do these experiments so we had to do the experiments over 2 different days. One being 27C and one being 26C room temperature. As an improvement to my experiment I could have put a lid on top of the beakers to stop evaporation taking place, as this was probably a major factor of heat loss throughout the experiment. I also could have put a corkboard underneath the beakers, as this would have reduced the amount of conduction of heat occurring from the beaker into the table. I could have also used a clamp and boss to hold the thermometer in a fixed position; by doing this I could ensure that the thermometer is always at the same place in the water.

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