Does air in the atmosphere suffer friction in some way due solely to the planet's rotation? I mean, if you took a rotating planet with an atmosphere (not being influenced or heated by its star, its nucleus or any other element), would the air get some friction only due to the planet's rotation? Does this slow down the planet's rotation?
$\begingroup$
$\endgroup$
2
-
$\begingroup$ Possible duplicates: physics.stackexchange.com/q/1193/2451 and links therein. $\endgroup$– Qmechanic ♦Jul 17 at 6:25
-
$\begingroup$ Cross-site duplicate: earthscience.stackexchange.com/q/25407/6 $\endgroup$– gerritJul 17 at 6:52
Add a comment
|
2 Answers
$\begingroup$
$\endgroup$
3
If an atmosphere were suddenly dumped onto a rotating planet, the planet would slightly slow down, some of the angular momentum is transferred from the planet to the atmosphere, to the point that the atmosphere rotates at the same speed as the planet. After which point, the planet would no longer slow down, as there is no air in the vacuum of space for the atmosphere to drag against and transfer any momentum to.
Due to conservation of angular momentum, only some weather effect accelerating the air faster than and in the direction of the planet rotation could actually slow the planet down.
The angular kinetic energy will not just disappear for no reason.
-
$\begingroup$ In the absence of external energy sources as per the question, is an atmosphere that is stationary relative to the planet actually in a stable equilibrium? Perturbations would still cause the atmosphere to experience Coriolis forces. I can't think of a good way to intuit whether the combination of this effect and friction still tends to return it to rest. $\endgroup$– WillJul 17 at 10:58
-
$\begingroup$ @Will As the planet (and atmosphere) rotate, I can imagine the atmosphere will, to some extent, bulge at the equator. After which point, I could imagine that as being a stable equilibrium, given the absence of external energy sources. $\endgroup$ Jul 17 at 18:40
-
$\begingroup$ @user16217248-on-strike the whole planet is an energy source though, so any tendency to amplify accelerations towards the poles on the face of it can transfer kinetic energy from one part of the atmosphere to another and ultimately from the earth to the atmosphere through friction; that isn't to say I'm sure the energy tranfers can arise from infinitesimal perturbations due to instability, but it's not clear to me that energy considerations are enough to prove one way or the other $\endgroup$– WillJul 17 at 23:16
$\begingroup$
$\endgroup$
In the absence of weather, the atmosphere rotates right along with the planet and so neither exerts any net torque or drag on the other.
I do not know if the air mass movements and mixing effects of weather produce any net drag on the surface of the earth; perhaps the experts here can weigh in on this.
answered Jul 17 at 4:50