Earth RotationSlide 2Slide 3Ve Decreases with LatitudeSlide 5Rotation, cont.Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Earth 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 sunEarth Rotation•Earth rotates about its axis wrt sun (2 rad/day)•Earth rotates about the sun (2 rad/365.25 day)•Relative to the “distant stars” (2 rad/86164 s)–Sidereal day = 86164 sec (Note: 24 h = 86400 sec)•Defines the Earth’s rotation frequency, = 7.29 x 10-5 s-1 (radians per sec)Earth Rotation•Velocity of Earth surface•Ve(Eq) = Re Re = radius Earth (6371 km)Ve(Eq) = 464 m/s•As latitude, , increases, Ve() will decrease•Ve() = Re cos()Ve Decreases with Latitude-80 -60 -40 -20 0 20 40 60 80050100150200250300350400450500latitude (N)Vearth (m/s)Ve() = Re cos()Earth Rotation•Moving objects on Earth move with the rotating frame (Ve()) & relative to it (vrel)•The absolute velocity is vabs = vrel + Ve()•Objects moving north from Equator will have a larger Ve than that under them•If “real” forces sum to 0, vabs will not change, but the Ve() at that latitude willRotation, cont.•Frictionless object moving north vabs = const., but Ve() is decreasing vrel 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 motionEarth 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 equatorCoriolis Forcean 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•Show Coriolis
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