Ask a Physicist: Introduction to Cavitation

Talitha, from Australia, writes:My boyfriend insists that if something moving fast underwater, the water wouldn't be able to move behind the object at the same speed and would create an air bubble. This doesn't seem right to me--please help!Talitha,So here's the deal: your boyfriend is almost right, but it's not quite an air bubble--the process he's describing is called cavitation, a name which comes from the word cavity.Have you ever seen cooking directions that need to be adjusted for differen...