Monday, June 18, 2012

plane journeys

i dont know why but people often ask me why plane journeys are different times in different directions for the same journey. everyone's best guess is that it's due of the spin of the earth, presumably because when the earth is spinning the opposite way to the plane it's a shorter journey.

most scientists know better and will say of course it's not because of the spin of the earth.

ironically, it is because of the spin of the Earth, but for a very different reason.

when the sun heats the earth, the poles get less heat than the equator. so there is a transfer of heat, via wind that takes hot air at the top of the atmosphere to the poles. cold air below it moves from the poles to the equator to fill the gap left (equalising the pressure).
due to the earth's spin, the coriolis force causes this wind, in the northern hemisphere to become an easterly wind (which counter intuitively means from the east, not to the east) near the equator and vice versa in the southern hemisphere. this causes an effective eddie current where at more northern latitudes, the wind's move in the opposing direction.

All this, is of course a generalisation, so only describes the overriding patterns that are found.

This is the explanation for prevailing winds (which leads to prevailing ocean currents). And it's these prevailing winds which cause the plane journey times to differ, as it's quicker to travel with the wind.

one last piece of counter-intuitive information is that when planes take off AND land they want to do both into the wind as this gives more stopping power and for take off, more lift!

kinda busy this weekend so forgot to play poker but have almost solve my c++ algorithm that was driving me mental.


Yakshi said...

Awesome. How do you know this?

Mudwig said...

i learnt it at university! there was one lecture on cool stuff. like anything that moves through water at any speed (boats of any size, ducks etc) all form wakes of 38 degrees. google tells me it was named after it's discoverer lord kelvin.

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