Answer: Newton's law of cooling
The curve is called Newton's cooling curve,the change in actual temperature with change in time( slope) will be ZERO(0) since the set temperature is constant.
Explanation: This law states that at constant conditions the change in temperature is directly proportional to time.
The slope =∆T/∆time
Where ∆T is the change in temperature plotted in the vertical axis in degrees Celsius and ∆time is the change in time in the horizontal axis in hours.
The hourly recording of the temperature and time under constant conditions in fridge will show a directly proportional relationship between change in temperature and the change in time.