Here's something we didn't cover in class, an explanation of the cause of the Coriolis force.  You'll probably find this a little confusing.  The pictures that follow aren't in the ClassNotes.  

An object flies by overhead


Imagine something flies over Tucson.  It travels straight from west to east at constant speed.  You would, more or less subconsciously,  plot its path relative to the ground.  The next figure shows the path that the object would appear to follow as it passed over the city. 





Here's the path the moving object would appear to follow relative to the ground.  Based on this straight line, constant speed trajectory you'd conclude there was no net force acting on the object.


The object flies by again but the ground is moving




In this second picture the object flies by overhead just as it did in the previous picture.  In this picture, however, the ground is moving (don't worry about what might be causing the ground to move). 

It's kind of like walking across the moving sidewalk at an airport with wet paint on your feet.  What sort of track would you leave behind?


It would appear that you moved across the sidewalk at an angle.  But that's just because the sidewalk was moving.

In the case of the object flying by overhead



The path, relative to the ground, also appear to moving at an angle.  It would no longer appear to be moving from W to E but rather from the NW toward the SE.  But it's still straight line motion at constant speed, so you conclude there was no net force acting on the object.

The object flies by a 3rd time but now the ground is moving and spinning.



Now the ground is moving and also spinning.  The object's motion hasn't changed.
The path of the object plotted on the ground has really changed, it appears to be curved.  But remember that's relative to the ground and the ground is spinning.  We could take the ground's motion into account (might be hard) or just ignore it (easier approach).  In the latter case you'd conclude that there was a net force perpendicular and to the right of the moving object.  You would need this force to explain the curved path that the object appears to be following.  And that's what the Coriolis force does.

The ground we stand on is spinning
At most locations on the earth the ground IS rotating (and this is what Foucault's Pendulum demonstrates).  This is most easily seen at the poles.



Imagine a piece of paper glued to the top of a globe.  As the globe spins the piece of paper will rotate.  A piece of paper glued to the globe at the equator won't spin, it will flip over.  At points in between the paper would spin and flip, the motion gets complicated.

The easiest thing for us to do is to ignore or forget about the fact that the ground on which we are standing is rotating.  We do still need to account for the curved path that wind will take when moving from one part of the earth's surface to anothere.  That's what the Coriolis force does.