# Q & A: Do planes have to correct for the Coriolis effect?

Q:
Hi, guys. I'm an aspiring physics student and can't quite wrap my head around something. I know that two points on a record move at different speeds while achieving the same number of rotations per minute; I sort of figure this is true on a sphere, as well. Specifically, I believe it holds true on the Earth. I've been crunching numbers, and figured out that Saint Petersburg moves at about 350 mph (60 degrees North equates to about 1/3rd the standard velocity of the Earth) versus Nairobi moving at an even 1040 (being right on the equator). If a plane takes off from Saint Petersburg it can head almost due south and end up in Nairobi's airspace, but actual pilots don't have to account for the 700 mph lateral ground speed differential between the two points.The standard answer is that air moves with the surface of the earth, but I'm wholly unconvinced that it could account for that degree of lateral acceleration without causing unmanageable turbulence.Anyway, could you guys either answer or point me to a book with those answers?---I realize this isn't quite the standard level of question you guys get, and doubt that I represent the standard students that ask them (I gather I'm fairly bright :P). Sorry, I just legitimately have nobody to ask. My teacher at school just looked dumbfounded when I talked to her after class.
- Caleb (age 16)
Huntsville, AL, USA
A:

The effect you're describing is called the Coriolis effect, if you want to read more about it.

I'm not sure why you don't think the motion of the air is a plausible explanation. The flight from St. Petersburg to Nairobi will take 14 hours or so, so there's a long time for the wind speed to gradually change without causing any turbulence. There can still be a small Coriolis deflection even with the motion of the atmosphere, and pilots would need to correct for that. But the prevailing winds (jet streams, etc.) have a much larger effect on headings and flight times. (Interestingly, these winds themselves are largely caused by the Coriolis effect, so it does actually have a major impact, just indirectly.)

For things that travel mostly outside the atmosphere (like ICBMs), or things that can't be steered after they launch (like long-range artillery) the Coriolis effect is very important and must be corrected for.

Rebecca H.

PS: Studying physics has a way of making you feel less and less knowledgeable the longer you pursue it... we get many questions from bright students that I'm unable to answer after six years of graduate school. But that's the fun!

(published on 10/27/2016)