Physics 101- Introduction to Mechanics
February 11- Newton's Laws






  Non-Inertial Reference Frames

The same fictitious force that "deflects" the ball thrown while on a merry-go-round, is responsible for the rotation of storms and weather systems.  The Coriolis force appears whenever you are in a rotating reference frame.

Air flows toward a low pressure region.  For the northern hemisphere, air moving down form the north is like the ball moving from the center of the platform toward the rim and it is deflected sideways to the west.  Air moving up from hte south is like a ball thrown from the rim toward the center, and it is deflected to the east.  (Note that this east deflection is greater than than the storm's natural movement to the east.)  The net effect is that low pressure systems (cyclones and huuricanes for example) in the northern hemisphere rotate counterclockwise.  Similar storms in the southern hemisphere rotate clockwise.


An even more dramatic example of non-inertial frames can been seen in accelerating rockets

When a rocket accelerates, an occupant feels "gravity".


An outside observer sees a horizontally thrown ball travel in a straight line.  Since the ship is moving upward while the ball travels horizontally, the ball strikes the wall somewhat below a point opposite the window.

To an inside observer, the path of the ball bends as if in a gravitational field.



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Jeff Phillips
Loyola Marymount University
Spring 2002