Question: What does the following graph tell us about the rate of cooling of water?
Graph showing how the temperature of a beaker of hot water changes when left alone (outside on a winters day).
Poor Answer: The rate of cooling is highest at the beginning of the graph because this is when the temperature of water is highest.
Good Answer: The rate of cooling is greatest at the starting time because this is when there is the greatest temperature difference between the water and the surroundings.
Note: It is best to write about Temperature Difference not highest temperature and discuss starting the time not just the start of the graph.