Dynamics - Design: The New Spoon Experiment

My hypothesis in Brief

The resultant force developed by the flow of water in a wave impacting upon the bottom of a surfboard is the primary force that makes the surfboard go (-i.e. changes its motion.) The more detailed version is contained in the thread ‘Dynamics – The Trim Equation’

But here’s the important design point, the flow that makes the surfboard go is impacting the bottom of the surfboard at an angle which is often close to being perpendicular to the bottom of the surfboard.

The Classic ‘Spoon Under the Running Faucet’ Experiment

There’s a example floating around (no pun) which is often used to explain how concaves (and convexes) work; the ‘spoon under the running faucet’ experiment. To run the experiment you take a spoon by the handle and place it under a running faucet so that the water flows more or less parallel to the handle or stem of the spoon. Basically if the concave side is presented to the flow, the spoon wants to move out of the way of the flow, if the convex side is presented the spoon is less inclined to move out of the way of the flow. The conclusions are obvious - concaves lift, convexes not so much – well, sort of.

The New ‘Spoon Under the Running Faucet’ Experiment

Here’s my new spoon experiment, let the water hit the spoon right in the middle of its spoony part, its bowl, concave side up. (The stem of the spoon is now at right angles to the flow of water.) Or turn the spoon over and let it hit directly on its convex side. In both cases the pressure on the spoon makes it go down. The conclusions are obvious, first, you didn’t really need to run this experiment to know what was going to happen, but if you did you now know that – impacting water (a flow) can make things move. If you think the spoon moves because gravity was pulling it down, you be partially right, so hold the spoon in the running water, then hold when its not in the running water, and ask yourself if it took the same amount of effort in each case.

But while you’re at the sink, start to angle the spoon a bit and see how you can get the water to shoot off it, this way and that. Here is the rough principle; if you can get the water to shoot of the spoon in ‘this’ general direction, a component of the force produced on your hand will be in the opposite direction. Admittedly, it’s rough, but generally in the broadest sense it’s true. (That force being produced on your hand is the propulsive force that I’ve been referring to in all these threads. Also, the experiment would make more sense if you were able to perform it upside, -i.e. with the water shooting up at the spoon.)

If you hang around the sink long enough, you will be able to start to sense the difference in force required to hold the spoon at different angles, whether convex or concave up towards the flow. You will also begin to sense the difference that a given angle or contour has with respect to downward, sideward, backward, or forward forces produced.

This is the nature of the flow that makes surfboards go. The classic spoon experiment still has value, not because it explains why concaves lift, but because it tends to address the kind of interactions that the once propelled surfboard will have with the ‘apparent flow’ or the flow of water the surfer sees from the standpoint of his surfboard. (But I’d be cautious in drawing any conclusions, such as the one in the classical spoon experiment.)

In Closing

My original final piece in this series was on the order of twelve pages and had all sorts of equations and diagrams, and grew a page or two every time I re-read it. I don’t think people would have read it, hell I probably wouldn’t have read it if I didn’t write it. The above spoon illustration seemed to be the solution.

The new spoon experiment will not tell you exactly how to design, but should make it clear as to how the propulsive flow is hitting your board (and your contours, and fins for that matter… think cant and toe-in, ‘which way does the water go when struck at this perpendicular angle?’) and hopefully serve as some reference as to what might be accomplished by using some contour or design element.

(Edit: 08/27/06. Corrected misspelling, kant to cant. KC)

It would be nice to run the experiment upside-down. If fact, I have. Worse, I made little balsa models of the contours that I was interested in. (Tip: Don’t do this in front of women, they will leave you, almost immediately.)

Finally, I am not an academic, nor a professional, nor anyone of note, nor likely to be in the future. Though I have a background in Mathematics (undergraduate), my knowledge, if any, of fluid mechanics has come through self-study. Which probably served me well, as I felt no need to memorize arcane terms, but only to understand concepts, appreciate when they might be applied, and move on.

Finally, if you’ve made it to here, thanks.

Kevin

(Edit: 08/23/06 Couldn’t resist, had to add the picture. KC)

I have been trying to bend this spoon

from the other room for 45 minutes

and the darn thing just wont budge.

mebe I need more chocolate chips

I think it looks a lot like

flat ware .

…ambrose…

stainless steel is also known as nickel steel

Try standing on your head.

love your shcool of thoughts, don’t stop thinking, nor sharing with us…

what about these women???

Hey, Ambrose, I can’t bend spoons either but chocolat chips are good. Had a friend went to a seminar and they did that spoon bending thing and every spoon and fork and knife in the kitchen drawer all bent on their own. OOPS!

I just stood by the sink awhile. All that sound of running wate–now I gotta pee

hee, hee! thanks again Mr. Curry for your thoughts. it’s always a

pleasure to read your posts…

in regards to the original post, i have to respectfully disagree completely.

i have a couple of arguments.

  1. the force that moves a surfboard across a wave is GRAVITY. the wave is a

hill that (hopefull) keeps building in front of the surfer. if a surfer is in trim, it

is because he or she is using the rail to use the speed gained from going

downhill to move sideways and always stay on the hill.

  1. in my 16 years of surfing, i have yet to see ANYBODY surfing where their

board was hitting the water at close to perpendicular (90 degrees) for more

than a second or 2. it seems, the only time the water is hitting the board at

close to 90 degrees is when the surfer is doing a really hard carving turn (and,

slowing down). for the most part, it seems more like the water is entering the

planing portion of the board pretty much parallel to the bottom plane. the only

part of the board that hits the water at an obvious angle is the area with the

entry rocker which is providing the small amount of lift needed to get the rest

of the board up on a plane.

and a couple questions for you:

  1. using your theory, why are steeper waves faster?

  2. when i look at a wave, why do i not see the water rushing up the face of the wave?

  3. how do you explain when a surfer gets a “sleigh ride” where he or she rides a

wave that does not break for quite a while?

thanks,

Chris

Quote:

My original final piece in this series was on the order of twelve pages and had all sorts of equations and diagrams, and grew a page or two every time I re-read it. I don’t think people would have read it, hell I probably wouldn’t have read it if I didn’t write it. The above spoon illustration seemed to be the solution.

Kevin

I have read all of it, including the equations.

You still haven’t shown that the equation F=PA is solvable in the context in which it was used in your theory ( a clue, it isn’t solvable).

Nor have answered the objection to your assumption that density implies pressure.

Or the fact that the only force opposing your ‘horizontal flow’ is the inertia of the surfboard and rider. … . none of your posts deal with this fact and the problem it causes for your theory namely that pressure will decrease as the surfboard accelerates horizontally, and reach zero when it reaches the same speed as the alleged flow. … . at a speed less than that of the wave front.

Instead, you deal with the objections by ignoring them, asking those who question you to leave, and then starting new threads which presuppose that the ‘proofs’ have been dealt with in previous threads !!

Then you rush ahead and give design advice on the basis of a theory which doesn’t work.

Thus it’s all Bunkum

:frowning:

Thanks.

Gravity can’t move something horizontally (i.e. perpendicular to its field, which is towards the center of the Earth.)

Mechanically, liquids interact with solid objects via pressure - a force but expressed per unit surface area. Please consider using these terms, and if you do, then consider where the forces are coming from, or how the pressures are developed.

See diagrams of wave particle motion, in prior thread Dynamics – The Trim Equation.

Also diagram provided, done quickly but I think it’s roughly correct.

The water particle velocity in waves is determined by wave height and period, not wavelength. As the wave shoals and increases in height, it gets steeper and the particle velocity becomes greater. The greater the magnitude of the water particle velocity impacting the bottom of the board, the greater the potential force developed, see prior thread Dynamics – The Trim Equation.

I don’t know why you don’t see water moving up the face of a wave, but it does, and if your standing in front of the wave that same water is also coming towards you. See diagram provided. The net flow is of course small until the wave breaks, but surfers aren’t interested in the net flow, just the flow on the face.

Sleigh riding just means that the surfer has presented the bottom of the board in such a manner that the combined surfer and surfboard weight do no cancel the vertical component of the force developed from the flow of water hitting the bottom of the board. Please see prior thread Dynamics - The Trim Equation.

Kevin

(Edit: 08/24/06. I had a moment to finish the illustration. It’s not a big improvement, but the progress of the little dots - water particles if you like - should help. And by the way, don’t hold me to the spacing of the dots, the point is to convey the progression. The dots loop but the loop is not closed, if such a regular spacing was continued. But even in deep water, the circles are not completely closed, and even less so as a wave shoals. It’s artificial, but all such diagrams usually are to some degree, and I haven’t the time, nor interest to work out the particulars for the particular period and height of the wave shown here.

And while I’m here I will explain what I mean by ‘lumped’. The term is used to refer to what you might call an averaged or net effect. Whereas each of the water particles will actually have a slightly different velocity vector, they are all hitting the bottom of the board and collectively produce a pressure - or force, given that force equals pressure times area, here the area being the exposed bottom of the board. KC)


the force that moves a surfboard across a wave is GRAVITY.

Nope. It’s Kinetic Energy that is the driving force. Not gravity. Gravity is surely the enemy of movement is it not?

Steeper waves are not necessarily faster. The enrgy in the wave is simply more focussed.

Your “sleighride” is dependent on the energy of the unbroken wave and the buoyancy of the board.

Quote:
Thanks.

Gravity can’t move something horizontally (i.e. perpendicular to its field, which is towards the center of the Earth.)

The only time a surfboard ever moves “horizontally” is when it is already moving and makes a turn across what you are calling horizontal. Clearly gravity allows this in the same way gravity on a snowboard or skateboard gives the vehicle speed and then the rider can turn 90 degrees and travel perpendicular to the center of the earth, and even continue turning another 90 degrees if he wishes and travel up hill for some period of time. Sometimes quite dramatically as in catching air out of a skate or snow halfpipe. In skateboarding and snowboarding, the surface of the halfpipe never moves and is not influencing the boards ability to continue sliding/rolling.

I still see no real “proof” that the water particles are doing much of anything to propel the board. From my view, the wave energy comes along, as there is less space between sea floor and top of water, the water is pushed upwards in a pulse. That rises the surfboard up. The surfboard then rides down that “hill”. If going down the line, the hill is continually building in front of the surfer, and he can go up and down the hill as he angles across, but in each case it is the “falling” that keeps the surfboard moving. Likewise, if a surfer heads straight to shore in the soup, the wave is still rising up behind him (whether you perceive it visually or not), near the tail of the board, and keeping the board flowing “downhill” all the way to the beach.

If you wish the readers to follow your discussions and be convinced of them, perhaps now would be a good time to put aside the physics terminology and write a few simple paragraphs using real world examples that may support your claims. I’m pretty sure my real world example of the skateboarder and snowboarder above disproves the statement of yours that I quoted. If you do not believe so, please provide a counter example or explanation. Cheers.

Hi Slim. . . making sense as usual I see !

Kevin could also try solving those equations of his too. . . (an impossibility !)

:

Quote:

Gravity is surely the enemy of movement is it not?

Do I have to tell you that this assumption has a very low truth content ? :0

Quote:

Gravity can’t move something horizontally

Yes it can. … . . . . gravity can give an obect kinetic energy, which can be redirected into horizontal energy (As Slim denonstrated) What gravity definitely can’t do is act as the ‘counterbalancing force’ to any horizontal water movement. . . . as claimed by yourself. In fact the only opposing force to horizontal water flow is the inertia of the object. . . . . once this is overcome then no further horizontal force can be applied. As I calculated on one of your previous threads, the work done when moving a 100kg object 5 metres vertically is about nine times as much as when moving it the same distance horizontally, and as the distance increases this difference becomes greater. .

nfotb – that’s a gem of a post! Good KoolAid, huh?

i find it very interesting thank kevins

i went snowboarding the otherday

it was epic conditions

and im not bad snowboarder.i can go down the hill and turn and the odd little ollie or fakie

i relized then and there that if i was to take the sport any further like bigger jumps etc

i would be more likely to injure myself.

so basically im at the my best i will ever be .becuase im old and value my bones

so at my level of basically going down the hill and turning etc

i find the sport pretty boring and overrated

why

cuz al you do is go up the the hill and down the hill

its all gravity

no variation

(the thrill people get is from jumping and the rush from potential injuring yourself)

surfing is completely different

there are so many different variables that make a surfboard go fast and turn well.

i can well see that your thoery is quite valid as a factor in what makes a surfboard go

to be a reasonable snowboarder all you need is money and a chair lift(ie go down the hill and turn)

to get good at surfing takes so much more effort and time(to catch a wave,stand up and turn along the face)

because there is so much more to it then just gravity!

go to sleep gravity heads

kevin might be wrong

but u deffinately are if you think its all gravity!

Quote:

i can well see that your thoery is quite valid as a factor in what makes a surfboard go

Sorry, Kevin’s theory is bunkum. . . . but I admire your blind faith, sort of. .

Okay, so I’ve been checking out these posts about trim and the dynamics of how a surfboard moves across the face of a wave for a while now and I think I’ll put my two cents in.

I’ve seen a few posts where people claim that a surfboard never moves horizontally except when turning. I suggest you guys get your selves copies of the Bruce brown films, and watch Phil Edwards and Renny Yater in trim on a clean point-break. When they get into trim, they are moving parallel to the surface of the water ahead of the wave. The board is at a slight angle to the horizontal plane, but the movement is horizontal. That is why they are in trim. They are balancing the downward force of gravity ant the upward thrust of the water flowing up the surface of the wave.

I’m no mathematician, but I would think that if you combined the forward speed of the wave with the deflection speed caused by the interaction of the water flow with the bottom of the board, that you could probably get a number that would correspond to the speeds of a board in trim. ( not including any pumping which involves another set of forces acting on the board to increase it’s velocity). The reaction of the water flow with the bottom also accounts for why cocaves and channels have a tendency to increase the forward speed of a board. Since the flow of water off the bottom of the board is generally at an angle somewhere near 45 degrees,( this info courtesy of the member who posted the very informative experiment with the plexi(perspex) board and tape to track water flow) if you redirect it to a more perpendicular release rearward you will get more forward motion out of it ala Newton’s law that for every action you get an equal and opposite reaction.

I think that’s about it. Tear away!

How the hell do you isolate gravity out of a trajectory (Kevin)? How the hell do you isolate wave push and grade out at the same time, when you’re talking about surfing, so that you get this one overarching, omnipotent force going the opposite way of everything else?

You can’t accept a combination of factors, a shifting balance of forces, a factor that multiplies a value over time? Why not?

“I don’t care about the facts!” “We believe in you Kevin!” “Sounds good to me, Mr President!”

What is the velocity and direction of this surface “flow” on a northbound 6 foot tall 15 mph wave in 8 foot depth?

Need some spoons?

okay

here’s one for you formulmatheholics stuck in these circular arguments

Quote:

MADRID, Spain (AP) – A reclusive 40-year-old Russian scholar has won the math world’s version of the Nobel Prize for cracking a conundrum called the Poincare conjecture – a breakthrough experts say might help determine the shape of the universe.

But Grigory Perelman shunned the Fields Medal, reportedly because he is disillusioned with academia, in an unprecedented rejection of the coveted prize.

Colleagues say Perelman also seems uninterested in a separate $1 million prize he could eventually win for proving the theorem, which concerns the nature of three-dimensional space.

What did he help solve…

was the Poincare Conjecture

Quote:

In mathematics, the Poincaré conjecture is a conjecture about the characterization of the three-dimensional sphere amongst three-dimensional manifolds. Loosely speaking, the conjecture surmises that if a closed three-dimensional manifold is sufficiently like a sphere in that each loop in the manifold can be tightened to a point, then it is really just a three-dimensional sphere. The analogous result has been known to be true in higher dimensions for some time. The Poincaré conjecture is widely considered one of the most important questions in topology. It is one of the seven Millennium Prize Problems for which the Clay Mathematics Institute is offering a $1,000,000 prize for a correct solution.

there you go this guy just solved the unsolveable theorem of how to topologically map the three dimensional space of the entire universe.

Maybe someone here can ask him to solve this rather simple problem than trying to solve a problem involving something as big as the universe…

he obviously performs these feats of genius for fun

least we forget that what happens in our space here is insignificant in relative terms and maybe we should quit making more out of it under the facade of intellect or art than it really is…

Just having fun and forgetting about life through intense focus

thats all

Quote:

least we forget that what happens in our space here is insignificant in relative terms and maybe we should quit making more out of it under the facade of intellect or art than it really is…

Nothing is insignificant, all things are connected, and I, for one, am not putting up a facade.

I disagree with the implied idea that because a mathematician just won a prize, that we should all give up thinking about the physics of wave and surfboard motion because he is supposedly so much smarter than us and our quest is so insignificant. . . it isn’t and we are not!

And by the way an argument which goes back and forth is NOT a circular argument. . . a circular argument is a particular kind of logical fallacy.

But hey it’s good to hear from you Oneula !

Roy