… as in so-and-so claims to have channelled with a dead relative.
Consider the funnel presented with a flow as sketched in the diagram.
The fluid flows, F volume per unit time, through the area A1 at the speed V1 = F/A1 (By the way, volume per unit time divided by area gives speed, which is of course, length per unit time.) Conservation of mass - though not universal like the law of conservation of energy, is found to be applicable for the kind of water flows generally observed in sports such as surfing, skiing, boating, etc. and, in this case demands that the same amount of fluid that enters the funnel also leaves it. Now, given the smaller area of the exit, this would require that the speed of the fluid leaving the funnel would have to increase relative to that at the entrance. In particular, V2, which is equal to F/A2, will be greater than V1, since A2 is smaller than A1, F being the same. In effect, you’ll have a created a jet, which you can then use to propel yourself(?).
Wow?
But wait, it gets better! You see the faster the water shoots out the back of the funnel, the faster you’ll go, and the faster you go, the faster the water will shoot out of the back of the funnel, and … well, maybe you get the picture. Heck, there’s no limit to the speed you could reach – watch out photons, here we come!
So build a funnel and put in under your surfboard, and just make sure you’re strapped in?
Gee, seems simple enough, how come nobody has come up this before? Well, they have, still do, and will likely continue to do so in the future. In fact, I met a fellow in the line-up the other day that had funnel fin on his board. He loved it and stood to do a good five minutes on why it worked… luckily, the sets were slightly more frequent.
But all that aside, is this possible, and if not, why not? In particular is it possible to put a funnel on the bottom of a surfboard and expect a little extra zip, or anything for that matter, as a result?
Here’s my answer, at least with regards to achieving some extra zip, no.
Here’s my reasoning. Whereas conservation of mass is definitely being obeyed, so is conservation of energy. The application of this latter principle becomes immediately clear (then again maybe not) when you realize that in order to hold the funnel in place you’ll need a force to do some work for you, in particular, you’ll have to change to momentum of the flowing fluid, which is just another way of saying you’ll need a force. In this case, such a force will appear as resistance, as in ‘resistance to motion.’ Heck, it’s not even a zero sum game. A lot of the work done on the fluid will take the form of heat and will simply be lost to the environment. In the end, the whole thing will tend to slow you down.
That’s not to say that the flow that’s there [under your board] can’t be tapped and used in creative ways, it’s just that there are constraints and basic physical principles [laws?] that must be considered, or you’ll wind up believe you’ve created the impossible – a perpetual motion machine – which you will not have done, because they don’t exist, at least they don’t appear to exist in this Universe.
But hey, perhaps I’m being a bit hard on ‘creativity’ – better to be objective and open-minded. So, please don’t let what I’ve written here stop you from sending whomever your easy payments of $19.99 per month - hopefully you’ll let us know how it works out.
Next time “Fins that move out of the way.” or “The Joy of Crabbing.”
kc
