Convection
This is when heat is transferred by substances that can flow (liquids such as water) and carry heat energy from hotter areas to cooler areas by their own movement.
- As liquids or gasses get hotter, particles move faster causing it to expand and become less dense.
- The liquid or gas will now rise up and be replaced by, colder, denser regions.
Radiation
This is when the heat energy is transferred by waves. Hot objects (cup containing hot water) emit mainly infrared radiation, which can pass through a vacuum (no particles are needed to transfer energy). However much radiation is given out or taken in by objects depending on its surface. A black surface emits a lot of radiation but also absorbs a lot of infrared waves. A white surface emits little radiation
Cup used
Prediction
I predict that these factors will affect the efficiency of the material
The lighter the material in colour the better insulator it will be. I predict this because light colours are poor radiators, therefore they will reflect the heat back into the cup, obtaining the waters warmth. The darker materials will absorb the heat and release it the other side so is a bad insulator.
The thickness and density of the material will also have a significant impact on the materials efficiency. Air is a very poor conductor, so materials with lots of large air pockets will be good insulators. For the material to have lots of air pockets it has to be less dense and quite thick. The air trapped in the pockets will prevent convection currents and trap warm air. These factors will help to reduce heat loss. A poor insulator will be thin with small if any air pockets, allowing heat convection and conduction increasing heat loss rapidly.
Based on the above evidence I predict the following for the different materials. Tin foil – Although this material is very thin, its shiny surface will reflect the radiation back into the cup and there will be a layer of air between the cup and tin foil to insulate it. Bubble wrap – This material has many pockets trapping air and air is a good insulator. Its particles are not close together so particles that have heat energy can not pass on energy as quickly as particles that are close to each other.
I think these materials will be the best insulator whereas the cup with no insulator will not be as good at keeping the water hot. It will give out more heat at the same rate. This is because there is nothing to trap in the heat whereas the other cups have layers of air which acts as an insulator.
Equipment
Kettle – to boil water.
Cup x5 – each cup used for each different insulator test.
Water (hot at 100°C) – fair test and easier to measure how much heat is lost.
Measuring cylinder – fair test, so we know how much water we pour in each cup.
Thermometer – fair test, make sure at beginning of all experiments, the starting temperature is the same.
Stop clock – to time each experiment exactly for 4 minutes (240 seconds)
Insulating material – to find out which material is the best insulator.
- Bubble wrap
- Paper
- Tin foil
- Cotton
- Cup (no insulator)
- Heat mat – this can prevent surroundings damaging.
Safety Precautions
I will also take a number of safety precautions whilst conducting the investigation.
It may be a good idea to wear any sort of protective clothing because at water’s boiling point it can be dangerous as it is possible to get burnt. So the kettle should be used safely and hot water is transferred securely. Using a heat mat may also be relevant as explained above in the equipment list.
Fair Test
Throughout conducting my investigation I will take a number of precautions to ensure my experiment is fair.
- The water starts at the same temperature (90°C – wait for water to cool from 100°C).This will enable me to assess the cooling rate accurately.
- The same amount of water is used (170ml). Different amounts of water will largely affect the cooling rate making the experiment inaccurate.
- The same amount of material is used. Although the materials might be different in thickness etc. it is important that they cover the same area.
- I will repeat each experiment three times. This allows me to achieve an accurate and fair result.
- The same material cup is to be used otherwise the test would not be inaccurate.
Method
- Set up equipment similarly as shown below.
- Wrap one layer of insulation around cup.
- Heat water to 100°C (boiling point).
- When water is ready, pour 170ml in a measuring cylinder, then pour it into the small paper cup.
- Put thermometer in and wait until it cools down to 90°C.
- Start the stop clock.
- Observe the temperature change every 30 seconds and record.
- Stop the clock after 4 minutes (240 seconds)
- Allow the cup to cool down to its original coolness then repeat the tests two more times with the same insulation.
- Lastly repeat the tests with the remaining insulation three times (repeat steps 1 – 10 again).
Results
The shaded red area is the temperature readings measured in degrees (°C).
Insulation: Nothing
Insulation: Cotton
Insulation: Tin foil
Insulation: Bubble wrap
Insulation: Newspaper
Analysis of Results
Observing the graph on the following page, my results clearly show a steadily decreasing gradient because the water is obviously losing heat by each second. The steepest line is the one which loses the most heat. Consequently, we can conclude which is the most efficient insulator that can keep the water in the cup the warmest. The materials in order of efficiency are tin foil, bubble wrap, newspaper, no insulation and lastly cotton (tin foil being the most efficient.
Conclusion
This does not match my prediction entirely because I predicted that the bubble wrap with many air pockets would be the best insulator. However the tin foil happened to be the best insulator. This means that the primary factor in preventing heat loss is stopping convection currents and trapping warm air. The reduction of convection currents must have been greater than the radiation to make this material the most efficient insulator.
The two most inefficient insulators were the white cotton and the cup alone (no insulator). This reason for this as backed in my prediction is because the thickness/density of the material causes a layer of insulating air. Hence preventing convection current and trap in warm air. Explanation for the non-insulated cup to be unable insulate properly is because it does not have a insulating layer to make the heat reflect back into the cup let alone trap in air.
Evaluation
The investigation was fair and the experiments I conducted achieved the required results. The experiments were fairly accurate and produced correct answers with barely any anomalous results. One of the results I had suspected to be incorrect is the amount of heat loss of the cotton. According to my background information the cotton should be more able to insulate the paper cup more than the cup alone but my results do not represent this. I think this result was an anomaly because with an insulating layer, there should be air in between to keep the cup and contents warm. A poor insulator, or even, no insulator, will be thin with small if any air pockets, allowing heat convection and conduction increasing heat loss rapidly.
If I conducted the experiment again I would use a wider variety of materials such as wider range of colours. I would want to do this because then I could investigate further into how the colour of the material affects my results. I would use the same material but in different colours for each test. I would also use the same colour material but in different textures e.g. woven pleated, platted, knitted etc. Also to acquire more reliable results, I could do the experiments repeatedly for a number of times. This will also avoid anomalies. If more advanced technologies such as accurate temperature reading equipments were accessible, it would enable a more accurate evaluation of results.
The method I chose to use was successful and worked well within the investigation, it was stable and fair. I would not change the method if I repeated the investigation. Overall I think my investigation was successful as it achieved the required results fairly and accurately, answering the set hypothesis.