Rate of cooling Essay Example for Free

Rate of cooling Essay 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 i C (4200J/kg i 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. Convection Convection mainly occurs in gasses and liquids gases and liquids are very poor conductors so convection is usually dominant process. When convection cant 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 doesnt happen in solids because there are no particles movement. Radiation 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 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. Variables 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 its a fair test e. g. volume of water, room temperature, size of the cups etc. Hypothesis 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.