The Coriolis Force is an
inertial pseudoforce (not a real force -- it's just
pretending. Like the so-called
centrifugal force) and is an effect of the
noninertial reference frame of an object that rotates at
constant angular speed ω. As an example, we will consider a
man at point B (near the edge of a large circle) and a
woman at point A (closer to the centre),
point A being a
distance of r
A from the
centre, O, and B being a distance of r
B away. The circle is rotating with
angular velocity ω. If A
throws a
ball to B, the ball will have velocity not just towards the location of B when the ball was thrown, but also a
velocity vector perpendicular to that, v
A. v
A must equal r
Aω, but it turns out that the man will not be able to catch the ball, because his own velocity, v
B (r
Bω), is greater than v
A, because, as was said earlier, r
A is less than r
B.
Now, let's look this over taking the spinning circle as our frame of reference. From this standpoint, A and B are not moving at all, and A throws the ball to B with velocity v towards B. However, due to the reasons stated in the previous paragraph, it appears as if the ball is attracted to the right and passes by A. It is as if a force is pulling the ball, perpendicular to v. This force creates an acceleration known as Coriolis acceleration, due to a non-existant force known as The Coriolis Force.
After a bit of arithmetic, too long to detail here (See if you can figure it out! Start out with rB - rA = vt.), we get the following equation that describes, Coriolis acceleration, acor
acor = 2ωv
The Coriolis Force has several interesting effects on Earth. Without it, air would be sucked directly into a region of lower pressure, but due to the Coriolis force, the winds appear to be deflected to the right and swirl around a low pressure area instead (clockwise in the Southern Hemisphere, counterclockwise in the Northern Hemisphere). This is why cyclones rotate in opposite directions depending on whether you are north or south of the equator. The Coriolis Force also explains the easterly trade winds near the equator. Also, an object falling from a height will be deflected slightly to the East, because of the Coriolis Force.