I just completed “Newton and the Counterfeiter” by Thomas Levenson.  I do not know if  the book is available on audiobook, but it would be a good book to enjoy on a trip.  

Circa 1660, Newton undoubtedly knew how fast the earth was resolving around the poles (the Greeks likely also figured it out 1k years before that).  But do your kids (and you) know?

The calculation is simple.  The radius of the earth at the equator is 3,963 miles.  The circumference of a circle is expressed as 2 x pi x radius or (2 x 3.14 x 3,963 miles).  The earth revolves once per day, and a day has 24 hours).  The answer should be in the form of miles/hr.  

I doubt that few people today could guess something even close to the answer.