Question

1. An experiment was devised to investigate the effects on the temperature of a cup of coffee when cream is added at different time intervals. Hot and cold water were used instead of coffee and cream. First, a container of water heated to 80°C was allowed to sit for 15 minutes. Its temperature was measured at regular intervals. Next, similar temperature measurements were taken for 15 minutes on a new container of heated water, but this time some cold water was added after the 2-minute reading.

Answer 1

Finally, the procedure was repeated except that for this last test, the cold water was added after the 12-minute reading. The resulting recorded temperatures were plotted on the graph shown here.

Answer 2

Based on the information given here, answer the following questions about the experiment.
• What question was asked in the experiment?
• What was the hypothesis, expressed as an if-then statement?
• What were the independent and dependent variables?
• What was the control in the experiment?
• Were there any sources of error in the experiment? If so, what?
• What could you conclude from the data?

Answer 3

Sources of error: hot and cold water were used instead of coffee and cream. The heat capacity of cream and coffee may differ from plain water. Nothing is said about the container used for the experiment, but if it is not a coffee cup, differing surface area and wall composition, etc. could make the overall cooling behavior different. Also, typically one would start drinking the coffee after making it and adding the cream, which would change the volume and again the cooling behavior. The experiment may well replicate the cooling behavior of a cup of coffee brewed and mixed with cream but then left untouched — who cares about that? :-) Another possible source of error is if the same container is used over and over for the experiment, it may be at a different temperature for different runs and affect the cooling behavior. That the heated water allowed to go 12 minutes before adding cream does not more closely track the initial heated water suggests to me that this has happened. Were I doing the experiment, I would prefer 3 identical containers and 3 batches of water with all the experiments going simultaneously to minimize any possibility of this.

The control is just heating up a container of water and allowing it to cool without adding anything. Then the experiment is repeated with the addition of "cream" at different points, and comparison of the resulting temperature curves to the first experiment.

The hypothesis seems to be that if you add cream to your coffee, then it will cool off (duh!) but adding the cream promptly after making it will keep the coffee hot longer than adding the cream later will do, if the coffee is steadily cooling after being made.

I think the question being investigated is whether it is better to add the cream promptly or to wait, if you want the coffee to stay hot.

The independent variables are whether or not cream is added, and if added, when it is added. The dependent variable is the temperature of the coffee.

My conclusion is that if I ever start putting cream in my coffee, I ought to do it as soon as possible, before the coffee has a chance to cool off significantly.

Answer 4

wow, this is so well stated, i honestly can't believe your level of intelligence and how you can remember this stuff off the top of your head!!

Answer 5

thank you so much, you always help me to understand these problems so much better

Answer 6

Thinking about the influence of the temperature and composition of the container: coffee mugs are usually nice and thick. Beer or soda cans are thin metal. They certainly don't have the same result on the temperature, do they?

Answer 7

Well, I just hope I don't lead you astray too often! It's been too many years since I studied this stuff...

Answer 8

@whpalmer4 hmm thats actually a very good point