The rate at which an object cools (i.e. how quickly its temperature decreases) depends upon several factors, including:

  • Surface area
  • Volume
  • Type of insulation
  • Temperature difference with the surroundings

For this investigation, the effect of the temperature of water upon the rate of cooling will be investigated. The temperature-drop over 5 minutes (600 seconds) will be measured for 200ml of water at different start temperatures. The average rate of cooling can then be found by:



  • digital stopwatch
  • 250ml beaker
  • rubber bung
  • thermometer
  • bunsen burner
  • tripod
  • gauze
  • retort stand and clamp
  • goggles

Control Variables:

  • Volume of water used: 150ml
  • Size of beaker (i.e. constant surface area): 250ml
  • Time interval of cooling: 5.0 minutes (600 seconds)
  • Temperature of the room: 21°C


  • Fill an empty beaker with exactly 150ml of water (check side-scale of the beaker)
  • Set up apparatus as shown above. Ensure the thermometer is about 2cm above the bottom of the beaker.
  • Light the bunsen burner and put on a blue flame. Heat up the water.
  • When the temperature on the thermometer has reached 90°C, immediately switch off the burner.
  • Start the stopwatch and time for 5.0 minutes.
  • Read the thermometer value at the 5.0 minute mark.
  • Before repeating the experiment, check the level of water is still 150ml (some may have evaporated) and add more water if required.
  • For different start temperatures, repeat steps 3-7 but turn off the burner at the desired temperature.


Start Temperature of Water (°C)Temperature after 5min (°C)Drop in Temperature



Average Rate of Cooling x 1000 (°C/s)


There is a strong correlation between the average rate of cooling and the start temperature: the greater the start temperature, the faster the average rate of cooling.


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