ESS229
Prof. Jin-Yi Yu
Inertial and Noninertial Reference
Frames
•In
formulating the laws of atmospheric dynamics it is natural to use a geocentric reference frame, that is, a frame of reference at rest
with respect to the rotating earth.
•Newton’s
first law of motion states that a mass in uniform motion relative to a coordinate system fixed in space will remain in uniform
motion in the absence of any
forces.
•Such
motion is referred to as inertial motion; and the fixed reference frame is an inertial, or absolute, frame of reference.
•It
is clear, however, that an object at rest or in uniform motion with respect to
the rotating earth is not at
rest or in uniform motion relative to a coordinate system fixed in space.
•Therefore,
motion that appears to be inertial motion to an observer in a geocentric reference frame is really accelerated motion.
•Hence, a geocentric
reference frame is a noninertial reference frame.
•Newton’s
laws of motion can only be applied in such a frame if the acceleration of the coordinates is taken into account.
•The
most satisfactory way of including the effects of coordinate acceleration is
to introduce “apparent”
forces in the statement of Newton’s second law.
•These
apparent forces are the inertial reaction terms that arise because of the coordinate acceleration.
•For
a coordinate system in uniform rotation, two such apparent forces are
required: the centrifugal force
and the Coriolis force.