Earth Rotation Earth’s rotation gives rise to a fictitious force called the Coriolis force It accounts for the apparent deflection of motions viewed in our rotating frame Analogies –throwing a ball from a merry-go-round –sending a ball to the sun

Earth Rotation Earth rotates about its axis wrt sun (2  rad/day) Earth rotates about the sun (2  rad/ day) Relative to the “distant stars” (2  rad/86164 s) –Sidereal day = sec (Note: 24 h = sec) Defines the Earth’s rotation frequency,   = 7.29 x s -1 (radians per sec)

Earth Rotation Velocity of Earth surface V e (Eq) = R e  R e = radius Earth (6371 km) V e (Eq) = 464 m/s As latitude, , increases, V e (  ) will decrease V e (  ) =  R e cos(  ) 

V e Decreases with Latitude V e (  ) =  R e cos(  )

Earth Rotation Moving objects on Earth move with the rotating frame (V e (  )) & relative to it (v rel ) The absolute velocity is v abs = v rel + V e (  ) Objects moving north from Equator will have a larger V e than that under them If “real” forces sum to 0, v abs will not change, but the V e (  ) at that latitude will

Rotation, cont. Frictionless object moving north v abs = const., but V e (  ) is decreasing v rel must increase (pushing the object east) When viewed in the rotating frame, moving objects appear deflected to right (left SH) Coriolis force accounts for this by proving a “force” acting to the right of motion

Earth Rotation Motions in a rotating frame will appear to deflect to the right (NH) Deflection will be to the right in the northern hemisphere & to left in southern hemisphere No apparent deflection right on the equator

Coriolis Force an object with an initial east-west velocity will maintain that velocity, even as it passes over surfaces with different velocities. As a result, it appears to be deflected over that surface (right in NH, left in SH)

Coriolis Force and Deflection of Flight Path

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