To investigate the rate of cooling in three different types of cups
The problem for this experiment is to investigate the rate of cooling in three different types of cups. They will be used as typical coffee cups for commercial purposes. The cups a polystyrene cup, a paper cup and a plastic cup.
Water has a high specific heat capacity. This makes it a very useful material for storing and carrying heat energy. Its heat capacity is 4200 joules per kilogram per °C (4200J/kg °C).
This is how water compares with other material:
Calculating heat energy:
4200 J heats 1 kg through 1 °C
8400 J heats 2 kg through 1 °C
84 000 J heats 2 kg through 10 °C
You could also calculate the result using an equation
heat energy = mass * specific heat * temperature
gained capacity rise
(J) (kg) (J/kg °C) (°C)
Heat tends to flow away from a hotter object to a cooler surroundings. Heat is mainly lost I conduction, convection, radiation and evaporation. For this experiment I will be only using convection, radiation, evaporation because conduction is mainly in solids.
This is a preview of the whole essay
Convection mainly occurs in gasses and liquids gases and liquids are very poor conductors so convection is usually dominant process. When convection can’t occur, the heat transfer by conduction is very slow.
Convection only occurs when the more energetic particles move from hotter region to a cooler region and take their heat energy with them. Convection doesn’t happen in solids because there are no particles movement.
Radiation travels through anything transparent. Heat radiation is given out by anything warm or hot. The amount of it that is absorbed or released depends on the colour and texture of the material.
Heat radiation is also called infra-red radiation. It consists purely of electromagnetic waves of a certain frequency. All objects continually absorb and release heat radiation. The hotter the object the more heat radiation it release.
Dark surfaces absorb more heat radiation than bright surfaces. Silver surfaces reflect nearly all heat radiation falling on them.
Evaporation is when water vanishes without boiling it to change into gas. This is because some liquid molecules move faster than others and the ones close to the surface may escape and form a gas.
These are things that may change during an experiment
The independent variable: These are things that I will decide to change e.g. the material of the cup, replacing equipment.
The dependent variable: This is the measurement that is effected by the independent variable e.g. the rate of cooling.
The control variable: These are the things that I will try to keep the same so I can make sure that it’s a fair test e.g. volume of water, room temperature, size of the cups etc.
I predict that the polystyrene cup would cool down the slowest because it has thick walls and when you go to restaurants and ask for a hot drink they give it in polystyrene cup. I think the paper cup will cool down the quickest because its made out of paper and paper has thin walls and it absorbs water.
- Polystyrene cup
- Paper cup
- Plastic cup
- Electrical kettle
- Measuring cylinder
- Glass beaker
- Heat resistant mat
- I preheated 400 ml water in the glass beaker until the temperature reached 75 °C while setting up the experiment.
- When the temperature reached 75 °C I poured 100ml of water from the beaker to the measuring cylinder.
- Then I poured the water from the measuring cylinder into the polystyrene cup with a covered cork lid and a thermometer.
- I took the readings of the temperature every 30 seconds for six minutes.
- I repeated the same procedure for the paper and plastic cup.
From my results I found out that my predictions were different. I was right in saying that the polystyrene cup was going to cool down the slowest.
Polystyrene is the best insulator because it has topped pockets of air in it and this reduces convection because air can’t move and heat has to be lost by conduction, which is very slow in air.
I was wrong by saying that paper will be the quickest to cool down, plastic was.
If I had more time I would have repeated the experiment three to five times. My conclusion is only based on one set results so it might not be right because theoretically paper should lose heat faster than plastic.
So if I repeat the experiment I will have fewer errors and more accuracy and I will be able to work out the average.
I would try to use better equipment e.g. digital thermometer so there will be less reading/human error.
The only problem I had was with the cork lid. The hole in the middle for the thermometer was too big which resulted in heat loss because there was some space for it to escape.