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
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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.
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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/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 60 800
50
100
150
200
250
300
350
400
450
500
latitude (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 will
Rotation, 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 motion
Coriolis Forcean object with an initial east-west
velocity will maintain that velocity, even as it passes over surfaces with different velocities.