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Physics question of the day
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trevorsmith

Since 25 Apr 2005
501 Posts
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PostMon May 16, 05 5:52 am     Reply with quote

if you have read it this far you have way too much time on your hands...and should be looking for wind

has any one been on a moving sidewalk like at the airport? Anyone ever see a piece of wood float up-river? (Assuming no wind waves)
Ever see a kid run with a kite and it is flying with no wind?

So yes a current will have more apparent wind on the kite. if you flew your kite on a moving side walk that was moving at 4 knots with 10 knots opposing wind, you would have 14knotts of apparent wind. There are a lot of variables, but a round estimate would be 14 knots.

Have you ever flown in the ocean, when a wave hits you, your kite looses a lot of power.

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PostMon May 16, 05 5:54 am     Reply with quote

Interesting problem. My part one response is that the river speed will not effect the kite force on a knot for knot basis until the kite is moving fast enough to generate some apparent wind, at which point one would draw some tip-to-tail vectors and find that the 4 knots would add to apparent wind in some ratio or another.

Boy, not a very technical response!

trevorsmith

Since 25 Apr 2005
501 Posts
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PostMon May 16, 05 6:19 am     Reply with quote

This is going to out to "Boy" guest..

First..create an account so we know who you are

Second..If you want a technical answer about Tip-to-tail vectors, e-mail Bill Nye the science guy, and throw away your KB mag. Cause "Boy" you worry to much about 4 knots.

"..until the kite is moving fast enough to generate some apparent wind" What are you talking about? Your kite since attached to your body, body moving at 4 knots = kite moving at 4 knots, you don't have to be swing your kite around to generate 4 knots of apparent wind, you just have to be moving hence "Apparent wind"

If you want a math formula to plug into your HP calculator, sorry I doubt you'll get it from this forum

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PostMon May 16, 05 8:46 am     Reply with quote

Trevor,

Not sure what my post did to annoy you, nor am I "worrying" about 4 knots. Hein posted an interesting problem, I assume for fun, I happen to think it's an interesting physics problem as well. I am working on an answer, in my slow deliberate manner. Bill Nye DVD's are north of $40, nor would they be of use.


I hope this forum does not become like kiteforum, in which kiters start to flame one another over really trivial stuff.

Besides, flamming people is rude and could be dangerous. After all, I could have played four years of Division 1 Water Polo for a top 10 university AND have an anger dissorder. Luckily, only ONE of these two are true. Not going to tell you which one though!

Happy Kiting

trevorsmith

Since 25 Apr 2005
501 Posts
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PostMon May 16, 05 9:10 am     Reply with quote

My original posting was for fun to untill I get "Guest" relpies saying "Boy, not a very technical response!" Refering people to as Boy is not Cool. Posting as Guest again when the Admin requests for you to create a login is also not cool

This forum is fun, and is not about flamming

That is why I was getting annoyed. Then you follow up with a Water Polo thing, anger disorder and making threats this could be dangerous! Also not Cool

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pkh

Since 27 Feb 2005
6548 Posts
Couve / Hood
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PostMon May 16, 05 9:28 am     Reply with quote

Okay guys... I think we can all agree that kiteboarding and Bill Nye both rock.

This place will not end up like kiteforum, I guarantee that...

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fokiten

Since 04 Mar 2005
188 Posts

Stoked



PostMon May 16, 05 9:32 am     Reply with quote

My my,,

You'd not last a day in my world,,LOL

Flames?? yeah; boy, that's pretty rough stuff indeed.

Now back on topic.

I'd guess, for an accurate wind function one would need to freeze the moment calculate all paramiters (dynamic system) log results, freeze the next instant refigure and so on...

This is how we calculate trajectorys for space crap.

And space is easy compared to an atmosphere, and the dymanics of infered forces chaging a baseline condition,,,it just goes bad...


We just ain't all that sharp...

every instant of motion must be frozen to calculate the forces.

To speak in general terms of totals for dymanic systems is to ignore the complications of ever changing stuff like profiles, to get techy you'd want to puke after the first three hours of checking your list of total influences/paramiters, ad infinitum.

Hey,, have fun but in reality,,,,I don't think anyone (I mean anyone) could answer this for a kiter, a kite a fluid dymanic air mass, water in motion... etc. ect.
It's just to complicated, now enjoy,,,boys wink

fokiten

Last edited by fokiten on Mon May 16, 05 9:50 am; edited 1 time in total

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PostMon May 16, 05 9:48 am     Reply with quote

My " not a technical response" was reffering to my own, not yours or anyone elses.

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PostMon May 16, 05 9:53 am     Reply with quote

Further clarification, "Boy, not a technical response" Was 'Oh Boy, my own response to this problem is not very technical."

trevorsmith

Since 25 Apr 2005
501 Posts
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PostMon May 16, 05 9:58 am     Reply with quote

Sorry if I misread that.

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kitezilla




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PostMon May 16, 05 10:04 am    physics question of the day Reply with quote

Hein,

will your hint involve the effect of waves on the kiteboard? Or the fact that water is a fluid about 800-900 times as dense as air? Or the fact that waves on a river, like the Columbia, have a different character than waves on a flat body of water? ( Standing waves as opposed to wind waves.......Have you ever surfed a river kayak?)

Enough said. got to go kiting in crappy SPI East wind.

barfly

Since 31 Mar 2005
1210 Posts
Seaside
BRACKISH



PostMon May 16, 05 10:19 am     Reply with quote

[quote="trevorsmith"]Have you ever flown in the ocean, when a wave hits you, your kite looses a lot of power.[/quote]

Fun with science indeed... purely hypothetical, but you feel the changes in apparent wind vs. true wind more on light days. Is it because you are trying to get on a plane and a board on a plane is less a slave to the current (though there is still effect of apparent wind)?

A light wind day on the coast with a moderate+ size swell seems to be a great test. Going through the break on a light day/bigger swell requires that you go way off the wind (downwind) to counter the "current" of the incoming swell. Heading back to shore on the same light day/bigger swell (especially if you are in front of a building breaker), you can be packed/overpow'ed. Miss that breaker and it rolls under you, you loose all that power; start pumping the kite.

When winds are higher (18-25kts) and you are packed on a 12M. Expect to be lit and even launching off the break on the way out, but you still have to bear off the wind after absorbing or jumping off the swell to beat the turbulance/current of the swells.

On the lost board scenario... I don't think you are going to get your board back if the current is strong 8+ kts and the wind is opposing. The board is not effected by the opposing wind, happy to cruise along in the current. You, on the other hand, have to beat upwind and against the current with an inefficent boat (your body). Top water polo players may pull this off, however. I've seen some people get upwind pretty well underwater by assisting the kite with some well timed dolphin kicks.

way too much time...

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gabe

Since 16 May 2005
475 Posts

Obsessed



PostMon May 16, 05 11:15 am     Reply with quote

to clarify, i was the guest who posted at 11:30, and then 3 replies around the 6. the other guest with the "oh boy, look how untechnical this is" is another person. i did not realize that lazy anonymity created identiy confusion and threats of anger release and flaming.

this is an interesting subject, and deserves thoughtful answers. intuition is often wrong. casual observation can also lead to incorrect theories. i would love to be shown wrong because then i would learn something.

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Hein

Since 08 Mar 2005
1313 Posts

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PostMon May 16, 05 12:38 pm     Reply with quote

Search on Free Body Diagrams

Remember that wind and current are not forces; Lift is.

And also the only way a force can be transmitted along
a string is by tension.

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PostMon May 16, 05 4:17 pm     Reply with quote

gabe wrote:
this is an interesting subject, and deserves thoughtful answers. intuition is often wrong. casual observation can also lead to incorrect theories. i would love to be shown wrong because then i would learn something.


very interesting and i'm sure my casual obs are only that. I suspect this discussion has asked more questions than it has answered

pkh

Since 27 Feb 2005
6548 Posts
Couve / Hood
Site Lackey



PostMon May 16, 05 5:07 pm     Reply with quote

me like kite.

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PostMon May 16, 05 8:37 pm     Reply with quote

When you are driving down the road at 60mph and stick your arm out the window, it feels like air is hitting it at 60 mph because air is hitting it 60mph. It feels like 60mph wind. If you are drifting in a river in still wind, the air will be hitting you at the speed the river is taking you.

If you are kiting in water going 4mph the opposite direction of the wind, it will feel like you are kiting in an additional 4 mph of wind.

In the SF bay, where I often kite, the current goes in and out with the tides and you really feel the difference in the apparent wind.

dt

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