Week 4

For the first four weeks of my course we learned about physics. To properly conclude our time in physics there has been plenty of reading for us to finish: (Chapter 7) Heat Transfer and Changing of Phase; (Chapter 8) Static and Current Electricity; (Chapter 9) Magnetism; (Chapter 10) Waves and Sound; and (Chapter 11) Light.
In our weekly thought conference we were presented with a scenario and were asked to provide an answer. The scenario given was: Suppose at a restaurant you are served coffee before you are ready to drink it. For it to be as hot as possible when you are ready for it, would it be wiser to add cream to it right away or when you are ready to drink it? Explain. I prefer hot chocolate, tea, or cappuccinos over coffee, but I am sure the majority of people must have coffee in the morning. I will also make the assumption that most coffee people may not have time to drink their coffee right away because they are busy taking care of other things (i.e. getting dress, getting the kids to school etc.). So they make their coffee to go and wait until they are all settled down before they drink their coffee. For you coffee drinkers, I provide you the answer to how you can keep your coffee as hot as possible so that when you are ready for your coffee it is not cold. When you get your coffee you should add your cream right away instead of waiting until you are ready to drink your coffee. But why?

Besides Newton's Three Laws of Motion, Newton also discovered Newton's Law of Cooling. Newton's Law of Cooling explains that if an object is hotter than its environment, then it will cool to match the environment's temperature; the same is applied to objects cooler than its environment. The rate at which the object cools is based on the temperature difference between the object and its environment; the greater the difference is the greater the rate of cooling.

When coffee is first brewed its hotter than the environment's temperature; assuming that you are using liquid cream that has to be refrigerated, the coffee cream will be colder than its environment. When the coffee and cream are separate they cool/warm quickly because they have a great rate due to their great temperature difference. However, when the coffee and cream are mixed together the cooling rate is smaller because their temperatures have balanced each other out. With a smaller a cooling rate, the coffee with cream takes longer to reach the environment's temperature, thus your coffee stays hotter longer.