epoxy vs. Poly

[Roy Stewart]

- surfboards don't have a motive source of their own. They harness that of the wave -

Surfboards are driven by gravity, and only indirectly by the wave. The amount of force driving the surfboard and rider is directly proportional to the mass of the surfboard and rider

I think the disagreement is probably keyed to the interpretation of the words people are using. Recently I have started pointing people to Lesson 1: Describing Motion with Words in an attempt to reduce these kinds of misunderstanding.

I think you are talking about Velocity, as opposed to Speed. All those horizontal and vertical zig-zags that modern shortboards do have more speed, no doubt about it. But their velocity is far less than my current 9'6"... Which is less again than, say, one of your 17'ers!

Sorry - I am a little bit of a physics/engineering geek

Speed and velocity are the same thing sorry, it isn't possible to measure speed without a vector qauntity . . . . the only difference between the two terms (as used by yourself) is the scale. . . . speed is being treated as distance divided by time using smaller time periods whereas velocity is distance divided by time over a larger time period. . . . . this is only a matter of the scale of the measurement. . . it's like saying that millimetres don't measure the same thing as metres, because they are smaller. Velocity is just as easily used to measure directional changes as speed is, because they measure exactly the same thing.

I do understand your point that by travelling further beween two points in the same amount of time due to directional changes en route one is travelling faster, (and with greater velocity!)

This is why larger gliders go faster than smaller gliders.

Larger wing area per mass allows greater lift. That is no guarantee of greater Speed, tho. A small, heavy glider may reach a greater speed... Partly because it will fall faster (as in an aerobatic glider)! But that doesn't necessarily give it a greater velocity (as in cross country and soaring events), where larger wings are a decided advantage.

Perhaps I didn't make myself clear.

What I meant was that if a glider is scaled up it will go faster. .. . . scaled up means exactly the same shape and density, this is because the gravitational potential energy of the glider increases with the cube as it is scaled up, but the drag it produces (a function of surface area) increases with the square. . . . thus the larger scaled object will always have a better thrust/drag ratio. This applies to surfboards as well, because surfboards are falling objects just like gliders.

I know that some Swaylockers have an understanding of Speed and Velocity which is well grounded in Physics. A few well beyond my own.

Possibly, although I am not so sure. .. . there are a few notable swaylockians with physics and engineering degrees who are still under the mistaken impression that any given wave will drive two surfboards of differing mass with the same force. . . . hard to respect that kind of mistake. .. .I find that qualifications are no substitute for clear thinking when it comes to physics, and i must say that as far as i am concerned, you are making more sense than some of the swaylockians who claim to be correct while spouting erroneous formulae, misquoting Newton, and constantly referring to their qualifications. Personally, i have learnt a lot from MTB and Blakestah, but as for some of the other 'experts'. . .. . .

Thanks for a great yarn

Likewise! Its always interesting and I always enjoy your clips. So do my wife and kids (esp ones like Glide Street).

Cheers!-doug

Cheers Doug here's one from last week, with gps speeds posted after trolling through many pages of data . . .. not a fast surf by any means , and my first time in the water for a couple of months (it shows)

Roy

http://www.olosurfer.com/4july2006gps.wmv

[IdRatherBeSurfing]

The velocity of an object is simply its speed in a particular direction. Since velocity is defined as a vector, both speed and direction are required to define it.

Speed (symbol: v) is the rate of motion, or equivalently the rate of change of position, expressed as distance d moved per unit of time t.

so speed and velocity are different . SIMILAR - but different

[Roy Stewart]

Well it is really a matter of definition. .. . I will go with yours if you like (that speed is velocity without direction)

An interesting consequence of this definition is that a racing car doing laps has no velocity if it returns to its original position.



Also it seems that another consequence is that an object has zero speed if we quote the direction of net movement, rather strange if you ask me, but if it helps to promote the Huntington Hop then it's all good.



Oh, and another point is that the gps unit can be set at a short interval (say half a second) and this enables it to record the speed during radical direction changes without being handicapped by the difference between the fastest moment and the overall direction of the ride., also the unit I am using takes into account VERTICAL movement as well, so there's really no way that shortboarders can complain about gps speed readings.

[Roy Stewart]

By the way, movement ALWAYS has a direction, therefore speed if defined as movement without direction cannot exist. . . . . . if speed is defined as movement without reference to direction, then the number in metres per second will be the same as the velocity over the same track.

Speed cannot exist without direction, because movement cannot exist without direction, therefore speed cannot exist without velocity.

All this new distinction between speed and velocity does is attempt to show that the net velocity of a track is not necessarily the same as the peak velocity over a portion of the same track.

The only difference between 'speed' and 'velocity' is that we are now supposed to assume that speed does not specify direction whereas velocity does.... . this is very misleading because all we are really doing then is ignoring the direction of movement. ... . . while the direction still exists !

[IdRatherBeSurfing]

hmmmm. but a 'wave' is classed as 'the transfer of energy without movement of particles' (I think, bear with me as A level physics was a long time ago) .

Somthing to do with the energy of the wave moves in one direction (forwards) but the particles in the wave move a miniscule amount (up and down)

ok ive been on the wetdog and will shut up now

[Baratacus]

no, you hit the nail on the head. Consider the example of a treadmill. Realative to the piece of rubber, you may be running 7 miles/hour. However in moving from point A to point B in space, you are going 0 miles per hour. On a track, your ground is stationary and your ground speed is equal to your movement from point A to point B. If a wave's water particles traveled with the swell, you're board would essentialy be stationary in relation to the water's surface but would be moving from Point A to Point B in relation to the space around you. Since the water particles of a wave are stationary however, Your movement through space would be equivilant to the amount of movement in relation to the particles of water you're skimming across.

did that make sense? It's 2a.m. here so maybe it won't make sense to me in the morning.

[IdRatherBeSurfing]

no, you hit the nail on the head. Consider the example of a treadmill. Realative to the piece of rubber, you may be running 7 miles/hour. However in moving from point A to point B in space, you are going 0 miles per hour. On a track, your ground is stationary and your ground speed is equal to your movement from point A to point B. If a wave's water particles traveled with the swell, you're board would essentialy be stationary in relation to the water's surface but would be moving from Point A to Point B in relation to the space around you. Since the water particles of a wave are stationary however, Your movement through space would be equivilant to the amount of movement in relation to the particles of water you're skimming across.

did that make sense? It's 2a.m. here so maybe it won't make sense to me in the morning.

woooooooo!!!!! Go me! :dances:

[Driftingalong]

I think what's trying to be stated IMHO...

speed:
rate of movement irrespective of direction. It is equal either to distance traveled divided by travel time, or to rate of change of distance with respect to time.

velocity:
a measure of the rate of change in position of something with respect to time, involving speed and direction


speed is not "without" direction but it is not concerned with direction.

So, if your traveling in a zig-zagging sort of fasion you may have a high rate of speed, but you are also at a lower velocity (since the velocity doesn't take into acount the entire distance just the overall change of position). Speed and velocity would only be the same if you travelled in a straight line.

[Roy Stewart]

Yes, but the point is that the gps unit can measure velocity over very short straight lines, thus it can measure the peak speed and velocity of an extremely zigzagged track just as easily as a slightly zigzagged or straight one. . . . thus the distinction between speed and velocity is completely irrelevant when measuring surfing speed via gps.

[dougirwin13]

I see a little of my "essay" is redundant :D But I'll post it anyway. Sorry it's delayed, but I wanted to give this the time it deserves.

Surfboards are driven by gravity, and only indirectly by the wave. The amount of force driving the surfboard and rider is directly proportional to the mass of the surfboard and rider

Energy physics tells us that gravity is simply the mechanism that allows us to release the stored potential energy of the wave. Without both a surfboard cannot work. Without a wave your board won't go anywhere. Without gravity the wave is useless. One of the basic laws of physics is "Energy cannot be created or detroyed, outside of a thermonuclear reaction, only moved".

Another way to think about it. Stand on your board on a flat ocean. Where do you go? Nowhere - you need a water wave for the energy transfer to occur.

Stand on a skateboard at the top of a slope and the board will go down the slope. But at some stage something had to get you and that skateboard to the top of that slope, so going down the slope is just releasing that potential energy.

My point was that surfboards do not have "drive" in the purist physics sense. That is they are not able to produce acceleration in and of themselves, just able to store and release external potential energy. So to me words like thrust and drive used by the surfing fraternity are mostly incorrect and inappropriate. That's not a biggie... But the confusion they can lead to is.

Speed and velocity are the same thing sorry, it isn't possible to measure speed without a vector qauntity . . . . the only difference between the two terms (as used by yourself) is the scale. . . . speed is being treated as distance divided by time using smaller time periods whereas velocity is distance divided by time over a larger time period. . . . . this is only a matter of the scale of the measurement. . . it's like saying that millimetres don't measure the same thing as metres, because they are smaller. Velocity is just as easily used to measure directional changes as speed is, because they measure exactly the same thing.

Sorry, but from a purist physics perspective they aren't the same at all. Like IdRatherBeSurfing quotes there are accepted meanings. And when we step outside of these confusion often edges in. I think a lot of the arguing on Swaylocks (I'm not just referring to you, it happens in plenty of threads you don't post in) is a result of that.

What I am saying is that HOW you measure velocity impacts the result. If you measure it as the time it takes to get from point A to point B where the two are 100 meters apart you will get one number. If you "chop" the path travelled into ten even slices you may find that you have travelled more than 100 meters. Maybe much more.

We need to use words with agreed meanings to correctly transmit ideas without misunderstanding.

I do understand your point that by travelling further beween two points in the same amount of time due to directional changes en route one is travelling faster, (and with greater velocity!)

Well... Not me! But established physics. Again, it depends on how you measure things.

Something else I find interesting - these small, light boards can't retain/conserve energy. They need to expend it. And if they do that by running out in a straight line away from the pocket indefinately they'll expend all their energy potential quickly, stop planing, then sink under the rider's weight. The only way they can work is by using that energy they are hemorraging to get back to the pocket and recharge. So they HAVE to freneticaly whiz around the wave surface and constantly go back to the pocket. Bigger boards don't charge up as quickly or easily, but they don't need to because of the massive amount of energy available in a wave. And because they conserve energy better and need less energy to plane and travel they can start further out, then plane through flatter and fatter sections. That elongates the distance between the start and end of the ride.

And yes, I have made some basic assumptions about board design ;)

Perhaps I didn't make myself clear.
What I meant was that if a glider is scaled up it will go faster. .. . . scaled up means exactly the same shape and density, this is because the gravitational potential energy of the glider increases with the cube as it is scaled up, but the drag it produces (a function of surface area) increases with the square. . . . thus the larger scaled object will always have a better thrust/drag ratio. This applies to surfboards as well, because surfboards are falling objects just like gliders.

Gravity cannot provide potential energy because it is a constant. Poetntial energy needs to come from an active source. Like a thermal or an air vehicle tow. In a sense large wing area allows more external energy to be stored as potential energy. Also, there are limits to scaling. For example a glider cannot be perfectly scaled up past a certain point, because the wings will fall off. The design of larger craft experiences more stress and has to be altered to compensate. Aeronatics theory and application is complicated for good reason :)

Scale has interesting physics all on it's own. A bee actually swims in the air (sort of). A cat can fall ten stories and suffer no serious injury. A small child will take a fall that will do us serious damage if scaled up, but they just walk away with a bruise, crying. The forces and pressures at work change with scale. That's why a scale balsa model of a DC10 works, whereas a real DC10 made of balsa would fall apart the first time you try to us it.

Possibly, although I am not so sure. .. . there are a few notable swaylockians with physics and engineering degrees who are still under the mistaken impression that any given wave will drive two surfboards of differing mass with the same force. . . . hard to respect that kind of mistake. .. .I find that qualifications are no substitute for clear thinking when it comes to physics, and i must say that as far as i am concerned, you are making more sense than some of the swaylockians who claim to be correct while spouting erroneous formulae, misquoting Newton, and constantly referring to their qualifications. Personally, i have learnt a lot from MTB and Blakestah, but as for some of the other 'experts'. . .. . .

Just because someone says they have a degree doesn't make it so :) Just because someone has a 50 year old degree doesn't make them right. I was speaking of people on there who have a good grasp of physics AND it's practical application. Degree or layperson - makes no difference to me. Definately agree re MTB and Blakestah.

Wave force is wave force is wave force. There are only really a few variables at work - how quickly a craft can store energy, how well it can conserve energy and how it releases stored energy. All the other things people talk about (drag, release, rocker, rail shapes, etc) boil down to those factors.

So a given wave has the same amount of energy regardless of board. A smaller, lighter board will pick up more of that energy... And haemorrage it almost as quickly. A bigger board won't pick up quite as much that quickly... These lighter boards are more critical about takeoff, they need to "take the drop" because they need to store a lot more energy to start working. But they cant hold onto that energy. Bigger boards need less energy because they conserve it better and need to release less energy to work -- so they are more energy efficient.

Cheers Doug here's one from last week, with gps speeds posted after trolling through many pages of data . . .. not a fast surf by any means , and my first time in the water for a couple of months (it shows)

Looks fine to me! I like it :)

so speed and velocity are different Wink . SIMILAR - but different

Correct!

Well it is really a matter of definition. .. . I will go with yours if you like (that speed is velocity without direction)

It's not really ours, tho. It's the terminology widely accepted from entry level physics onwards. I just think that's the safest to use for the sake of clear communication and discussion.

An interesting consequence of this definition is that a racing car doing laps has no velocity if it returns to its original position.

Yes, depending on how you measure! This is where I previously said that there are sensible limits to how we should measure.

Also it seems that another consequence is that an object has zero speed if we quote the direction of net movement, rather strange if you ask me, but if it helps to promote the Huntington Hop then it's all good.

Oh perish the thought! I hate that wretched, ugly hop! *shudder*

Oh, and another point is that the gps unit can be set at a short interval (say half a second) and this enables it to record the speed during radical direction changes without being handicapped by the difference between the fastest moment and the overall direction of the ride., also the unit I am using takes into account VERTICAL movement as well, so there's really no way that shortboarders can complain about gps speed readings.

Intersting... Since civilian access GPS satellites have a well documented granularity of 10 meters. Perhaps your unit has some additional circuitry, that'd also account for it being able to measure vertical movement at better than 10 meters.

By the way, movement ALWAYS has a direction, therefore speed if defined as movement without direction cannot exist. . . . . . if speed is defined as movement without reference to direction, then the number in metres per second will be the same as the velocity over the same track.

What about a treadmill? There's speed. There's direction. But there's no velocity.

Speed cannot exist without direction, because movement cannot exist without direction, therefore speed cannot exist without velocity.

Speed is the act of motion. A merry go round has speed, as does a child's spinning top. But but little direction or velocity.

All this new distinction between speed and velocity does is attempt to show that the net velocity of a track is not necessarily the same as the peak velocity over a portion of the same track.

It isn't new, mate. It's a well established fundamental of physics. And it deals with the separation of motion (speed) and travel (velocity). What it tells us is how we measure is important... And that words are important.

The only difference between 'speed' and 'velocity' is that we are now supposed to assume that speed does not specify direction whereas velocity does.... . this is very misleading because all we are really doing then is ignoring the direction of movement. ... . . while the direction still exists !

Physics can be like that - sometimes counterintuitive. Intuition tells us that two spheres identical in all respects except weight will fall at different rates - the heavier will fall faster. But that isn't the case.

Yes, but the point is that the gps unit can measure velocity over very short straight lines, thus it can measure the peak speed and velocity of an extremely zigzagged track just as easily as a slightly zigzagged or straight one. . . . thus the distinction between speed and velocity is completely irrelevant when measuring surfing speed via gps.

See comments about satellite GPS granularity above. Some frenetic shortboarder can do a big cutback or two in a ten meter cube... Maybe travelling 20 meters. Whilst I just cruise through it at ten meters. Takes us the same amount of time.

-doug

[Roy Stewart]

Hi Doug,

We are basically on the same wavelength, however I must just take you up on the small point below

Intuition tells us that two spheres identical in all respects except weight will fall at different rates - the heavier will fall faster. But that isn't the case.

In actual fact the satement above is a myth. . . . except in a vacuum.

In a gas, the heavier sphere will fall faster, because it has the same drag due to air resistance while having greater 'thrust' due to greater mass and thus greater gravitational potential energy. . . . and a superior thrust/drag ratio.

Similarly (this is the 'scaling' point I mentioned earlier) if we have two objects of the same density and shape, but one is larger than the other, then the larger one will fall faster in a gas. . . the larger object increases its mass (and its 'thrust') with the CUBE as its size increases (mass being directly proportional to volume for a solid object of even density), while its drag increases only with the SQUARE as size increases (drag being directly proportional to surface area).

An example which illustrates this well known point is that an identical 1/2 scale model of a glider will not travel as fast as a full sized one.

A lot of people make the mistake of assuming that because there is a maximum acceleration due to gravity, that therefore all objects are pushed with a constant force due to gravity irrespective of their mass. . . . this is incorrect, and is the mistake that a few Swaylockians made. . .. . what actually happens is that the gravitational force which attracts an object is proportional to the mass of that object. . . and thus if two objects experience the same drag, while one experiences greater gravitational force due to greater mass, then the the object with greater mass will fall faster in a gas (or a lquid). This is an indisputable and well known fact, and in my opinion, it is time that it was realised in the surfing world.

[Roy Stewart]

So a given wave has the same amount of energy regardless of board. A smaller, lighter board will pick up more of that energy... And haemorrage it almost as quickly. A bigger board won't pick up quite as much that quickly...

Sorry Doug but this isn't true

When a wave picks up two objects of different mass to the same height, the object with the greater mass has greater gravitational potential energy. . .. . and the wave has done more work in lifting the object with more mass. . . .

[IdRatherBeSurfing]

can i just say...

DO YOU HONESTLY THINK ANYONE REALLY CARES!!!!

u were still wrong about speed/velocity, so ner

[Roy Stewart]

Quit trolling, I was not wrong about speed and velocity, read my posts, I am well aware of the fact that speed is just velocity with an unspecified direction. . .. so what. . . speed and velocity readings are identical for speed surfing readings so it is a red herring anyway, and as for caring. . . . apparently a lot of people do care judging by the number of hits speed surfing discussions get . . . . .and if surfboard designers and builders don't care about what makes a surfboard move, then they should . . . ... and most don't have the foggiest idea, just blindly and mistakenly assuming that any given wave will drive surfboards of differing weigt with the same amount of force. . . . . . it's like a flat earth society out there the way supposedly educated people cling to their long held myths, and when they are shown to be incorrect they often flip out completely, as happened on swaylocks . . .

I repeat that the amount of force from the wave which moves a surfboard and rider is directly proprtional to the mass of that surfboard and rider. . . . . this is an indisputable fact.

[Baratacus]

dang.. lost my response.... I don't want to put all of that in again... basicallyI was going to agree with the Kinetic energy statement about the wave expending more work to lift the larger board. I think the argument that the shorter board has more energy and therefore is faster revolves around all of the forces that we are discussing here. The short board blows all of its energy in a quick burst down the face of a wave and must be lifted again to recharge for another burst of speed. A short board looses its plane at a much higher speed. Then it falls victim to drag and relys on its flotation to stay above the water. It has none so it stops. The long board has enough energy and momentum (inertia... dang... another scientific term to argue about) to cary it at a planing speed when the surf starts to flatten out. The long board has a much slower planing speed so it will still plane at relatively low speeds and when it slows below a planing speed it still has some flotation to possibly keep it on the edge of its plane with a quick paddle into the next section.

I don't think the short board has more energy or even equal enrgy to the longer board, it just has the ability to blow it all at once. Its like a Capacitor v.s. a Battery....

This is what I understand... is it wrong?

[Roy Stewart]

Makes sense to me anyway !

[dougirwin13]

Hey Roy!

First let me say - it's refreshing to disagree with someone online and not have it degenerate into name calling and other childish behaviour. Also, having to explain the way I see and interpret things forces me to think through them carefully, which I also enjoy. So thanks Roy.

We are basically on the same wavelength, however I must just take you up on the small point below
In actual fact the satement above is a myth. . . . except in a vacuum.

I think you must be referring to the fact that all objects will fall at the same rate in a vacuum. Note that I said "two spheres identical in respects except weight". That is very important. Same radius. Same surface texture. Same everything. Just different weight/density/mass (e.g., one might be somewhat hollow).

Gallileo proved that by formula and in the 60s it was only proven experientally by astronauts on the moon. Gallileo also showed that the time of fall of a given object is practically independent of its mass. And this has not been disproved since. In fact it balances perfectly well with all subsequent physics.

If you have a look at Physics Glossary PDF you'll see the following:
FFS = 6×pi×h×r×v = 2×r×pi×3×h×v
Where pi=3.14159, h=viscosity index, r=radius and v=velocity. Note - there is no reference to weight or density or mass.

You'll also find this definition:
Drag: The resistance to movement of an object through a medium, increasing with the viscosity and density of the medium and the surface area and shape of the object.

Again, no reference to mass.

My point was that sometimes physics can be counter-intuitive. Another example is that hot water freezes faster than cold water. If you want the proof and an explanation simply open Part 3 of the Physics FAQ and go down to Item 14 - "Hot Water Freezes Faster than Cold!".

On a side note, I find the history of physics fascinating (yes, I am a nerd). Lots of interesting material about Galilaeo can be found at the Galilean Library, including a particularly interesting tretise on The Galileo Affair.

In a gas, the heavier sphere will fall faster, because it has the same drag due to air resistance while having greater 'thrust' due to greater mass and thus greater gravitational potential energy. . . . and a superior thrust/drag ratio.
Similarly (this is the 'scaling' point I mentioned earlier) if we have two objects of the same density and shape, but one is larger than the other, then the larger one will fall faster in a gas. . . the larger object increases its mass (and its 'thrust') with the CUBE as its size increases (mass being directly proportional to volume for a solid object of even density), while its drag increases only with the SQUARE as size increases (drag being directly proportional to surface area).

Surface area matters, mass does not.

Where mass comes into it is this. An object with greater mass requires more force to be displaced by the same amount as a lighter object, all else being equal.

And no, a larger object does not fall faster in a liquid (gas is considered a low viscosity liquid in physics). A smaller object does. This is because drag/friction is higher on an object with a larger surface area. It's in the maths posted above.

Basically, all objects fall at the same rate in a vacuum. Therefore the viscosity of the liquid an object is falling in and that objects surface area (i.e., drag) are the only things that impede a given object from falling at that rate.

An example which illustrates this well known point is that an identical 1/2 scale model of a glider will not travel as fast as a full sized one.

Au contraire, mon amie! That is more about momentum and F=MA (Newtonian Physics), not about the physics of falling objects. Basically a larger object requires more force to move. As such it can store more potential energy, to be expended later. That said drag DOES come into it somewhat - the larger object experiencing greater drag, which means it falls less slowly.

A lot of people make the mistake of assuming that because there is a maximum acceleration due to gravity, that therefore all objects are pushed with a constant force due to gravity irrespective of their mass. . . . this is incorrect, and is the mistake that a few Swaylockians made. . .. . what actually happens is that the gravitational force which attracts an object is proportional to the mass of that object. . . and thus if two objects experience the same drag, while one experiences greater gravitational force due to greater mass, then the the object with greater mass will fall faster in a gas (or a lquid). This is an indisputable and well known fact, and in my opinion, it is time that it was realised in the surfing world.

Mass makes no difference in falling, surface area (translating to drag) does make a difference. The astronauts on the moon dropped a hammer and a feather and both hit the ground at the same time. That was captured on film. If you are correct that film would show differently. If you have a beefy glass or perspex chamber and a vacuum pump you can check for yourself.

Mass makes a difference in momentum and storing potential energy.

There are lots of things about physics that the surfing world either misunderstands or ignores. I'd like to see that corrected.

So a given wave has the same amount of energy regardless of board. A smaller, lighter board will pick up more of that energy... And haemorrage it almost as quickly. A bigger board won't pick up quite as much that quickly...

Sorry Doug but this isn't true
When a wave picks up two objects of different mass to the same height, the object with the greater mass has greater gravitational potential energy. . .. . and the wave has done more work in lifting the object with more mass. . . .

First things first. I am going to apologise for the "A smaller, lighter board will pick up more of that energy..." statement. It's misleading and doesn't say what I meant.

Yes, it takes more of the wave's energy to move the object with more mass. But why does a smaller, lighter board need to go higher up a wave and drop down a steep face? Whereas a bigger board doesn't need a bigger wave? And can take off lower down on a wave?

Because the smaller board needs to accumulate a higher level of energy. And then it looses that energy more quickly and has to recharge again. It's F=MA and drag at work again.

That's what I was trying to say. apologies for the confusion that one caused.

Quit trolling, I was not wrong about speed and velocity, read my posts, I am well aware of the fact that speed is just velocity with an unspecified direction. . .. so what. . . speed and velocity readings are identical for speed surfing readings so it is a red herring anyway, and as for caring. . . . apparently a lot of people do care judging by the number of hits speed surfing discussions get . . . . .and if surfboard designers and builders don't care about what makes a surfboard move, then they should . . . ... and most don't have the foggiest idea, just blindly and mistakenly assuming that any given wave will drive surfboards of differing weigt with the same amount of force. . . . . . it's like a flat earth society out there the way supposedly educated people cling to their long held myths, and when they are shown to be incorrect they often flip out completely, as happened on swaylocks . . .

I agree, that was a terminology thing which resulted in miscommunication. Judging by the high emotions on threads where this gets discussed a lot of people do care. And they seem to care a great deal.

I repeat that the amount of force from the wave which moves a surfboard and rider is directly proprtional to the mass of that surfboard and rider. . . . . this is an indisputable fact.

Yes... And no

Do you deny that a board accumulates more energy by taking off higher on the wave? It is lifted higher and absorbs more potential energy. But a bigger board doesn't need to do that... And a smaller board does. That's what I am getting at. A smaller board has to "charge up" as much as it can to work. And then it virtually haemorrages energy and has to "recharge" again. Naturally a bigger board can do this too. But it doesn't need to and it's trickier because of it's size. The bigger boards are more energy efficient.

Late takeoffs are almost a requirement for smaller boards. For larger boards they are... Optional.

Thanks again Roy. This is a good mental workout.

-doug

[Roy Stewart]

We are basically on the same wavelength, however I must just take you up on the small point below
In actual fact the satement above is a myth. . . . except in a vacuum.

I think you must be referring to the fact that all objects will fall at the same rate in a vacuum. Note that I said "two spheres identical in respects except weight". That is very important. Same radius. Same surface texture. Same everything. Just different weight/density/mass (e.g., one might be somewhat hollow).

Gallileo proved that by formula and in the 60s it was only proven experientally by astronauts on the moon. Gallileo also showed that the time of fall of a given object is practically independent of its mass. And this has not been disproved since. In fact it balances perfectly well with all subsequent physics.

Yes but that's in vacuum, I am talking about objects falling in a gas.

Galileo's two spheres did not hit the ground at the same time, they landed at "practically the same time" meaning that they appeared to land at the same time, however from the conclusion drawn from Galileo's experiment , namely that both objects would land at the same time in a vacuum, it necessarily follows that they could not have landed at the same time in a gas, and Galileo's experiment wasconducted in a gas.

In a gas, two spheres of identical size, shape, and surface texture, but differing in mass, will fall at different rates, the one with more mass will fall faster.

And no, a larger object does not fall faster in a liquid (gas is considered a low viscosity liquid in physics). A smaller object does. This is because drag/friction is higher on an object with a larger surface area. It's in the maths posted above.

Incorrect. If both objects are of the same shape and density, the larger one will fall faster. You are assuming that because the larger object has more friction it will therefore fall more slowly. However this is not true, because it is not the total amount of friction which determines which object falls faster, but rather the thrust/drag ratio (or force/drag ratio if you like). What happens with the larger object is that it has a better thrust/drag ratio. As stated earlier, the drag created by falling object is (all else being equal) directly proportional to the surface area of the object, and the energy which drives the falling object is directly proportional to its mass. So the object with the greater proportion of mass to surface area will fall faster. Now as an object increases in size its proportion of mass to surface area changes, which means that it has a better thrust/drag ratio and falls faster.
Unfortunately for Galilieo, this means that his larger sphere acelerated faster and would have hit the ground slightly sooner than the smaller sphere, provided that they were actually dropped from the same height and the ground was perfectly level. Galileo's experiment did not prove what it is reported to be proving because he was not in a vacuum.

Basically, all objects fall at the same rate in a vacuum. Therefore the viscosity of the liquid an object is falling in and that objects surface area (i.e., drag) are the only things that impede a given object from falling at that rate.

Yes, but it does not follow from the fact that objects of different weight will fall at the same rate in a vacuum that therefore objects of different weight are 'driven' by the same amount of force. . .. in fact more force is used to drive the object with more mass . . . even if this does not give greater acceleration in a vacuum. . .. . and thus, if both objects experience the same amount of friction then the heavier one will fall faster.. . . . with the exception that if both the objects have zero friction (as in a vacuum) they will fall at the same rate.

An example which illustrates this well known point is that an identical 1/2 scale model of a glider will not travel as fast as a full sized one.

Au contraire, mon amie! Basically a larger object requires more force to move. As such it can store more potential energy, to be expended later. That said drag DOES come into it somewhat - the larger object experiencing greater drag, which means it falls less slowly.

Of course a heavier object requires more force to move it, but in the case of the force of attraction between objects, the heavier object always has more force in proportion to its greater mass, and will only fall more more slowly if it has proportionally more friction in relation to its mass, which it doesn't... . . in fact it has LESS friction in proportion to its mass and will fall faster

Mass makes no difference in falling, surface area (translating to drag) does make a difference. The astronauts on the moon dropped a hammer and a feather and both hit the ground at the same time. That was captured on film. If you are correct that film would show differently.

Mass makes no difference to the rate of descent in the absence of friction (as in a vacuum) but it does make a difference when friction is added, because friction subtracts from the maximum possible acceleration due to gravity, and it does not do so in proportion to mass. . . . .one object can have proportionally greater friction than the other, and thus fall more slowly.

I repeat that the amount of force from the wave which moves a surfboard and rider is directly proprtional to the mass of that surfboard and rider. . . . . this is an indisputable fact.

Yes... And no

Do you deny that a board accumulates more energy by taking off higher on the wave? It is lifted higher and absorbs more potential energy. But a bigger board doesn't need to do that... And a smaller board does.

Yes a board accumulates more energy by taking off higher, I was talking about two boards sitting side by side and then being lifted to the same height, then taking off together. . ..

Thanks again Roy. This is a good mental workout.

-doug

Cheers Doug, please excuse me for picking on the points where we disagree and ignoring the ones where we agree.

[Driftingalong]

I would have to say that you are right Roy...
If a shortboarder rode their board the way you ride your tank (basically standing and crouching in one place), you would beat them.
However, any skilled shortboarder could have taken off deaper and still smoked you on that wave in the video.
I've seen shortboarder go faster than that on even smaller waves!


At least Doug is backing up his statements with research/physics pages. You just simply state "that's untrue" and move on. Where's your back up, or are we just supposed to believe what you say.

[Baratacus]

Its not the just the height of the wave, the wave has to be hollow for a shortboarder to drop in to it. Unless you're talking about a 5' tall 100 lb. grom that can actually float on a 6' potato chip. When you have a one to two foot wave that isn't forming up into a nice hollow pocket, you can't force a shortboard into it. Even if you pop/launch into it and paddle till it planes, the board won't be able to maintain its speed unless it has a steep enough face to accellerate down. A short bord can't travel at the speed of the waves forward movement and remain in a hydroplane. A shortboard has to move down the face to stay up to speed. When it runs out of face it has to cut back and try to find some more. Depending on the video you're refferencing, most of those vids on the Olo were on waves that had shallow faces and the board was traveling at the speed of the waves forward movement. A long board CAN plane at that speed. There were no short boarders that could catch that since it wasn't forming up and peeling.

These two guys have an understandng between them and if you have even a rudimentary education in physics you can follow along and what they say makes sense. If you have a question to a specific comment or think its a load of bull, ask them to prove it or show you where it's written and I'm sure they'd search it out and provide you a link. It's nice that they can discuss this with each other without getting hostile. It'd be nice if you could keep it civil as well.