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Joined: Mar 2000
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Carpal Tunnel
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Carpal Tunnel
Joined: Mar 2000
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...apparent [E.A.] speed of the point is going to be slow when it's near the ends of the line and fast when it's near the center.Actually® anyone who's ever played in a marching band or danced with the Rockettes will tell you the speed differences are much more than merely apparent, being faster on the outside and slower as you near the center. But are we talking apples and oranges here? 
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Joined: Dec 2000
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Carpal Tunnel
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Carpal Tunnel
Joined: Dec 2000
Posts: 13,803 |
The linear speed will be greater the farther from the center the trombone player is, assuming the same angular velocity (i.e., speed measured in degrees per second). The center I referred to above was an apparent center of a line segment formed by the one-space projection of the circle on the (e.g.) y-axis, no point of which would correspond to any point on the circle closer to the center of the circle, of which they ain't none anyway being how as all points on a circle are equidistant from the center.
If you can't lure them with logic, baffle them with bullshit
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Joined: Oct 2000
Posts: 5,400
Carpal Tunnel
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Carpal Tunnel
Joined: Oct 2000
Posts: 5,400 |
Yes, a marching band, or the wheels on a truck have a differencial.. (by an large, trains don't, so curve on trains are much wider and rounder than curves on roads.. but there are other differences as well..)
a differencial gear (actually several gears,) allows the inner wheel to turn slower than the outer wheel.. In marching bands, the rows on the inside of the turn take smaller steps, and the rows bunch up a bit.. the marchers on the out side of the turn take larger steps, and the rows splay out slightly.
but i hadn't thought of the tide working the same way--
especially because High tide in lower manhattan come at a different time that high tide in greenwich CT, about 25 miles away.. (something else i have never quite understood)
i guess its sort of like a wave in a stadium.. High tide is standing, low tide is sittting, and high tide moves..but looking at the local tide tables, its doesn't make too much sense..
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Joined: Jul 2000
Posts: 1,094
old hand
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old hand
Joined: Jul 2000
Posts: 1,094 |
Well, it's sinusoidal, innit?The height of the water is, yes, but to figure out the speed of the tide you have to take the derivative of the sin curve, which happens to be the cosin curve. Where the sin curve crosses the x-axis (halfway between it's highs and lows) the cosin curve reaches it's maximums and minimums, meaning that the speed of the tide will be greatest in the middle. I hope that was clear. 
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Joined: Mar 2001
Posts: 4,189
Carpal Tunnel
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Carpal Tunnel
Joined: Mar 2001
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tidesWhat Faldage just discussed and more is all right here, rkay...including an animated figure and charts. A complete study of tidal cause and affect. http://www.sailingissues.com/navcourse6.htmlThe Only WO'N!
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Joined: Dec 2000
Posts: 544
addict
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addict
Joined: Dec 2000
Posts: 544 |
Per our beloved belM: thermocline was not just a difference in temperature of the water but the visible line that is created where the different waters are separated.
I find that the line is a lot easier to see in a lake where there is much less wave action than in the ocean. Most often the waters even have different clarities.
This line isn't always visible, but it is the line that divides a mass of water of one temperature from a mass of water of higher or lower temperature. My experience with it is from diving - typically when you're in the water the thermocline isn't visible, but sometimes you can really tell when you cross it - get 30 or 40 feet down and bbrrrrr!!!
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Joined: Sep 2001
Posts: 6,296
Carpal Tunnel
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OP
Carpal Tunnel
Joined: Sep 2001
Posts: 6,296 |
Found this online about the white squall (myth or not): The white squall may be myth, or it may be a microburst. If they form during daylight you might see the approach as a line of broken water or whitecaps rushing at your vessel, but usually they appear out of nowhere.
"The Pride Of Baltimore, a fine 137 foot schooner, was reportedly struck by a white squall. The 121-ton vessel sank about 240 miles north of Puerto Rico, casting the surviving crew members adrift for five days. The Toro, a Norwegian freighter picked them up at 2:30 a.m. May 19th, 1986.
"Here is an eyewitness account of the sinking: ‘A tremendous whistling sound suddenly roared through the rigging and a wall of wind hit us in the back. The Pride heeled over in a matter of seconds. The 70-knot wind pushed a 20 foot high wall of water into the starboard side. She sank in minutes.’"
A USATODAY.com graphic shows what a microburst is. While the graphic shows what a microburst can do to an airplane that’s taking off or landing and much of the research into microbursts was prompted by the danger to aviation, microbursts have caused other kinds of damage on the ground and I know of at least one case in which a microburst overturned a boat, killing 11 people. http://www.usatoday.com/weather/askjack/waoceans.htm...interesting to read there about the "microbursts." Also read several pro and con movie reviews of this film. Yeah, there are problems, but the shots of the ship in the sea are terrific.
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Joined: Oct 2000
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Carpal Tunnel
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Carpal Tunnel
Joined: Oct 2000
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I only use this line for effect, but my parents used it, often..
Worse things happen at sea
with WWII not to far behind them, i guess for them, no matter what the peril, nothing was as bad as what could happen at sea.
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Joined: Jun 2001
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Carpal Tunnel
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Carpal Tunnel
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I once witnessed something akin to a white squall. I was working in a small restaurant facing East Grand Traverse Bay when a huge wind (microburst?) caused several birches across the street on the water's edge to topple. Looking across the bay, I saw a wall of white and nothing else. The whole thing lasted only 15 to 20 minutes, but when it was over, several boaters had lost their lives. My daughter and her girlfriend had barely made it to the friend's house to shut the windows when it hit. They were two terrified young girls, I can assure you. The friend's house was in a wooded area on the shore of the same bay. The boaters were lost in West Grand Traverse Bay on the other side of Old Mission Penninsula.
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Joined: Jan 2001
Posts: 1,156
old hand
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old hand
Joined: Jan 2001
Posts: 1,156 |
OK, sorry to be away for so long, but I've been out with a cold. Here are some definitions from my list, you guys already got some of them yourselves, of course - what else would I expect from such a group?  Advect - (verb) to be "dragged along" with the current. Little oceanic suspended things, like plankton, are advected - they move where the current goes - they can't swim of their own accord. Velocity can also be advected. (Now try and wrap your minds around THAT - I'm still not pleased with it myself!) The noun is "advection". Bathymetry - this one was right - the measurement of ocean depth and ocean "features" (rifts and ridges and stuff) Drogue - dammit, I have to look this up at school since this list had been compiled ages ago - It's a parachute-like thingy that is dragged along with the current and served some purpose in old-style current measuring instruments Eddy - Jackie is right, swirly things. Specifically, eddies are called "mesoscale" features because they're neither tiny like surface waves nor "basin-scale" like the Gulf Stream. Usually about 100-600 km in diameter, they're self-contained swirly bits of ocean, extending to great depths (i. e. not just surface features). Fetch - stales got this one (of course), the distance of open water across which wind blows, which affects the size of surface waves (bonus points for stales because he got that part, too) Seiche - we pronounce this "SAYsh" - you guys collectively got this one, it's like a bathtub wave. It's a resonant wave in an enclosed area, like a harbour. It can have a number of causes but the net result is some pretty amazing changes in water level. My prof has some great photos of a seiche a few years ago in Petty Harbour, which also affected St. John's harbour, and by sheer luck the associated flow anomaly was measured by some ADCPs (Acoustic Doppler Current Profilers) moored in St. John's harbour. Sill - this is a ledge of shallower water, for example, again in St. John's harbour, there is a sill. The harbour is about 30 m deep in the main part, but at the mouth of the harbour (the Narrows) there is a big ledge, where the depth is only 10 m or so. This has ramifications on how often the water "trapped" inside the harbour (in the part deeper than the sill) is flushed out into the sea. Swell - this is specifically surface waves generated elsewhere, which will be obvious because they don't go in the same direction as the prevailing wind where you are observing them. They are easy to observe as the slow up-and-down of the water. If you pay attention you'll realize most of the time they are not going the same direction as the local wind. This means they were caused by a storm somewhere else, and have taken a fair bit of time to travel to where you are. Thermocline - this one's been covered pretty well - it's the region of the sharp change in temperature that separates the upper ocean layers from the deep ocean. Typically this is at 200 m depth. The layer above the thermocline is well-mixed by surface winds but the layer below is unaffected by winds. Turbidity - helen (I think it was her) got this one right one - no need to add to it. Vorticity - the tendency of a fluid to move in a circle. It has a mathematical definition, too. It has important consequences for when eddies move into water of different depths, for example. Doldrums - the region near the equator where winds are generally calm. There are oceanic/atmospheric reasons for this which I can't recall at the moment. Something to do with atmospheric cells (and of course Coriolis forces!) Fjord - I'm sure most of us know this one but the word has a great ring to it - those steep ocean inlets like in Norway - and Newfoundland, and Labrador! Designed by Slartibartfast, I believe.
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