A catering company is deciding how thick the foam lining of a reusable food container should be.
In the first trial, a container is filled with hot soup. The initial temperature of the soup and its temperature after a fixed cooling time are recorded.
An identical container and soup from the same batch are used for a second trial. Both trials take place under the same room conditions.
Which procedure for the second trial would allow the company to test the effect of foam thickness on the rate of cooling?
Fit a thicker layer of the same foam, using a larger soup mass but the same initial temperature and cooling time.
Keep the original foam thickness, using the same soup mass and initial temperature but a longer cooling time.
Fit a thicker layer of the same foam, using the same soup mass, initial temperature and cooling time.
Fit a thicker layer of a different foam, using the same soup mass, initial temperature and cooling time.