The scenario of the Coriolis force described to me is as follows: A water mass is moving from the north to the south. An earth based observer would see this mass move in a straight line; however, an observer from space would see the water mass curve. If this space observer was looking in the same direction as the water mass was moving (in the northern hemisphere), he would see the water curve to the east (right). This part I understand, since this is the direction the earh rotates. Now if this space observer were in the southern hemisphere this same water mass would curve to the west (left). Huh? Can someone please help me visualise this southern hemisphere scenario?
OK, picture that you’re in Mexico and your buddy is in Canda, and you’re throwing a baseball back and forth. You are closer to the equator, and are therefore spinning around with the Earth in a larger circle than your Canuck friend. When you throw the baseball straight towards him, it’s going to have more sideways momentum because of its spin around the Earth, and that sideways momentum will make it miss to the right (the direction of the Earth’s spin).
Similarly, when your friend throws to you, it won’t have enough sideways motion to keep up with your speed, and will miss to the right from his point of view (your left).
So when you have huge masses of air, and the air is trying to go into an area of low pressure, the air coming from each direction misses to the right, causing a counter-clockwise swirling. The effect is opposite for high pressure areas where the air is going outwards, and it’s opposite for the Southern hemisphere.
My general trick for visualizing the Coriolis effect is to imagine that your are on a carousel with someone. Your friend is standing at the hub - they very center. You are on near the edge, and you throw a can of Pabst Blue Ribbon to your friend. Fortunately, you’ve thrown it straight at your friend, so it goes nowhere near him.
Why? The carousel is moving clockwise - to the left as your face your friend. Your friend is not moving at all, only spinning slowly. So the can of PBR has a leftward vector added to the hubward vector that you imparted to it, so it goes sailing off to your friend’s right.
All of this would be reversed if the direction of the casousel is reversed - which is exactly what happens to the Coriolis if you’re in the southern hemisphere. (As you probably know, this is why hurricanes in the northern hemishere blow clockwise while southern ones blow counter-clockwise; things are deflected to the left in the southern hemisphere, whether they’re moving south or north).
Originally posted by **Stylus **
Reading the OP more carefully, I think this is somewhat mistated. The water mass, moving from the south to the north in the northern hemisphere, is deflected to the west, relative to the rest of the earth. Now, you might be thinking, this makes no sense - everything on earth is moving eastwards at all times! True, but let’s not forget that equatorial stuff is moving east much faster than polar stuff (and the poles themselves aren’t moving at all). So our northern water mass, moving southwards from a relatively slow-moving part of earth (e.g., near the Aleutian Islands), is at a disadvantage relative to the more hurried pace of waters, say, in the central Pacific. Thus it appears to an earthling to be deflected west. It’s hard to say what an observer from space would see - obviously the whole surface is moving east so fast that maps from space would probably not be stationary from a space perspective; rather, they would correct to a single point on the ground. In other words, to get a clear picture of events on our carousel, you kind of have to run around it in circles.
Anywhere in the Northern Hemisphere, the deflection will be to the right, regardless of whether you’re moving north or south: If you’re moving from the Equator northward, then the deflection will be to the east.
It’s also important to note that significant changes of latitude are necessary for the Coriolis Effect, so it won’t make any difference in your toilet or bathtub.
Thanks all! I cannot believe I forgot the equator is rotating faster than the poles! That piece of the puzzle makes all the difference.
Historical note. The coriolis force became REAL important in the Boer war. Why??? think about it.
Cool demo. As a former AP Physics teacher…
Ya’ need:
a large spinning platform (like a record player, but bigger - maybe the “lazy Susan” from the fridge.
Pan (as in for cooking brownies)
big can (not your tushie, a can larger than a soup can. Maybe one that kidney beans come in.
Wire and wood to build a frame.
Here’s what you do:
Build a u shaped frame that kinda looks like this
l l
l__ l
l l
l _______l
and put it on the platform. The __ halfway down the left side is a little platform on which the can will sit.
Punch a hole in the can, on the side, near the bottom.
Take wire and wire can to frame with hole pointing to center.
Put pan in bottom of frame, on turntable.
Put finger over hole and fill can with water.
Remove finger and spin platform.
Watch from above and be amazed!!!
The idea is that the water will pour from the can in towards the center of the circle (when viewed from above). This allows the coriolis force to be “viewed”.
gotta preview, gotta preview, gotta preview
sorry 'bout that sucky picture! the sides should “line up”.