Today, a wind blows by us. The University of Houston's College
of Engineering presents this series about the machines that make
our civilization run, and the people whose ingenuity
Aerodynamics is all about flow around airfoils or golf balls or
submarines. It's about gases and liquids parting to move around
solid bodies. But fluids have an odd property that we didn't
really see until the invention of the airplane drove us to look
more closely. It is that fluids stick to bodies. That means two
kinds of drag affect any body. One's the pressure that builds up
as, say, your moving car pushes air aside. The other is fluid
dragging on the surface -- the kind of resistance you feel when
you pull a knife out of a cold jar of honey. That resistance
adds to the pressure drag when you drive down the highway. If
you could get very close to the surface of your moving car and
measure the speed of air next to it, you'd find it moves at the
same speed as the car. But that speed falls off sharply as you
move away from the sur