Large bathtub-like vortexes
Jearl Walker  www.flyingcircusofphysics.com
May 2013 You are familiar with the vortex that can form when water drains from a bathtub. The direction of swirling is set by the pre-existing (but probably imperceptible) swirling in the water, due to the initial pouring of water into the tub or by your motion while bathing. As water flows toward the drain, the vortex builds up until it can be appreciable. The water going down the middle of the vortex comes from the surface.

Here is the same type of vortex but on a larger scale, with far more energy. Water drains through pipes from one lock to another so that a boat might be able to move up or downstream on a river. As the water rushes into a pipe, a large vortex forms with a noticeable hollow center.

http://www.youtube.com/watch?annotation_id=annotation_997938&feature=iv&src_vid=T4DGICW5_6I&v=6g5KqIfCmFk

Here are two vortexes in water draining from a flooded field. There has to be a drain pipe beneath each.

http://www.youtube.com/watch?v=Ct_17xYGNz8

And here is a vigorous vortex in what appears to be a river. Here again there must be a drain below the vortex but I do not know if it is a pipe. The other possibility is that the water has broken through the top of a cavern and water is now pouring into the cavern.

http://www.wimp.com/whirlpooleverything/
https://www.youtube.com/user/astichs/videos same video

That type of nightmare situation occurred in 1980 in Lake Peigneur in southern Louisiana. A long-established salt mine stretched out beneath the lake, where salt was carried out from a large salt dome that had long ago been pushed upward by the surrounding rock bed. That bed also had oil deposits, and in November, 1980 an oil company began exploratory drilling to locate the oil. According to the company’s calculations, the drilling site was well away from the salt mine. However, someone made an error in the location because the drill pierced the roof of one stretch of the salt mine. The engineers knew something was wrong because the drill bit seized up with salt, and yet there supposedly was no salt in the way. When the drill bit was pulled up, water began to pour from the lake into the hole and into the salt mine.

All of the salt miners managed to escape before the water dissolved the salt walls and filled the mine. The entire drilling rig disappeared into the vortex that formed over the hole. The vortex also captured several barges and one tug boat, sinking them or pulling them down into the widening hole. As water poured into the mine, it rammed the air in the mine up and out of the mine, creating a 400-foot high geyser. The lake did not go dry only because the water flow through an adjacent canal reversed itself, bringing water from the Gulf of Mexico into the lake. Water drained into the mine for two days. Here is a documentary about the disaster:

https://www.youtube.com/watch?v=ddlrGkeOzsI

So, the next you watch the soap bubbles disappear into the vortex over a bathtub drain, think about how much destruction a lake-size vortex can do.

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Pub tricks
Do you want the pub-trick stories here at the FCP site? Use the following links and then scroll down a page or search for "pub trick". Keep in mind my point --- anyone can do a pub trick but the real trick is to explain it without bluffing or just waving your hands in the air. Physics = the power to explain.
Chapter 1 archives
Water and the disappearing cigarette  click this
Balancing a coin on a folded paper edge  click this
Lifting a bottle with a thumb and one finger, click this
Hanging spoons from the nose, click this
Hanging bottle caps on your face, click this
Standing eggs on end  click this
Removing a lighter from under a bottle  click this
Removing a bill from between balanced bottles  click this
Removing the cork from a wine bottle  click this 
Balancing a hammer and a lorry  click this
Champagne cork as a morter round   click this 
Removing a coin from under a mug   click this 
Hanging a bottle on the wall  click this
Matchstick rocket  click this
Transferring a steel ball between beer mats   click this 
Tying a ring hitch click this
Chapter 2 archives
Reversing an egg in a tequila glass  click this
Blowing out a candle   click this
Escape from a cellophane pocket  click this
Exchanging water and whiskey   click this 
1000 drops from an empty bottle   click this 
Yard of ale and beer boot click this
Collecting grains of black pepper click this
Tia Maria wormy action click this
Vortex in a bottle and the vortex beer bottle   click this
Making straw paper stretch and crawl  click this
Making a ketchup packet float and dive  click this
Lifting rice with a rod click this
Inflating a long sandwich bag click this
Toothpick design trick click this
Using glug-glug to clear beer foam  click this
Egg tricks  click this
Raisin in champagne  click this
Inverted can of Red Bull   click this
Chapter 3 archives
Moving match sticks on a glass rim
Popping a plastic straw
Chapter 4 archives
Slam-freezing a beer or soda
Lighting a candle
Cooling beer on a hot day
Picking a shot glass with the palm
Rattling a coin
Chapter 5 archives
Rotating a matchstick balanced within a glass container