Timmy’s

You buy a large coffee (300 ml) at 80° and four milks (15 ml each) at 4°, and get into your car which stays at a constant temperature of 16°.  It will be a 10-minute drive before you can drink the coffee, and you want it to be as hot as possible at that time.  Do you put the milk in at the beginning or after the 10 minutes when you’re ready to drink it?  Do you mix first and then drive or drive first and then mix?  Does your intuition give you an answer?

This activity draws on Newton’s Law of Cooling and is a nice application of exponential decay.

I’ve worked many problems with teachers over the years.  And when I meet them at a conference after a long time, this is often the problem they remember. Why?

Because they’ve “been there, done that.”😊