Newton's law of cooling. The rate at which body temperature changes is proportional to the difference between body temperature and ambient temperature. The cool drink was removed from the refrigerator and left in a room where the temperature was 80 ◦F. Express the temperature of the beverage as a function of time (min) if the temperature of the beverage when it was removed from the refrigerator was 40 ◦F, but after 20 min it heats up to 50 ◦F.