dougirwin13 wrote: - 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
dougirwin13 wrote: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!)
dougirwin13 wrote:RoyStewart wrote: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.
dougirwin13 wrote: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'. . .. . .
dougirwin13 wrote:RoyStewart wrote: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 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)