Fifteen feet across and thirty inches deep, old vinyl swimming pool wasn't terribly useful for swimming. I was twelve and its novelty had worn off. The obvious uses were floating or just trying to stay cool in the Summer, but it turned out to make a lovely wind tunnel and general piece of experimental apparatus.
My Dad liked ice cream enough that he found five gallon cartons that our freezer could barely hold. These were very sturdy and the empties were useful. It turns out you probably don't want to try it, but I though I could launch a model rocket from under water by covering the top with something the rocket could fly through.1 But somehow the idea of moving through water - flying through water - caught my fancy.
Plastic model airplanes were common back then and I had the idea that I might be able to fly once of them. After all, the better ones had a bit of an airfoil molded into the wing. What I didn't know at the time was this was a good idea. Water and air are both fluids and the motion of a body through them is governed by the same fluid dynamics. The difference is water is about 800 times denser than air. It took quite a bit of experimentation, but finally I had a nice "wind tunnel" that replaced air with water.2
You've probably done the same with your hand out the car's window. The airflow against your hand creates quite a bit of drag, but you can change the shape of your hand by cupping it a bit to resemble an airplane's airfoil and something wonderful happens. There is lift - the same sort of lift that allows flight under the right conditions - enough, depending on the angle of attack, to make it challenging to hold in place when the car is at highway speeds.3 This same airfoil can be used underwater as a hydrofoil when we swim and gives a neat window to examine of some the Olympic swimming events as well as how those of us who are less skilled and athletic manage.
Brynne suggested swimming as the next Olympic topic and Jean triggered something about airfoils. A nice topic as there has been an enormous amount of research into swimming since the 70s. Computational fluid dynamics, a discipline fueled by the aerospace industry, had advanced to the point where it was possible to study the basics of a human moving through water and competitive swimming has been revolutionized mostly through improvements in technique.4 After all - things moving through water behave very much like things moving through really dense air - the sort of thing I was learned from that little vinyl wind tunnel, er, swimming pool when I was twelve.5
While runners and cyclists go forward by pushing off of solid surfaces, swimmers move forward by pushing against the fluid they are flying through. You cup your hand a bit and control the angle it makes with the water. Just like an airfoil there is gravity, drag, lift and propulsion - the propulsion is from the lift pointing mostly forward. Fortunately the human body has almost the same density as water, so very little work has to be done to support yourself against gravity.
There are three basic types of drag that try to hold a swimmer back - friction, pressure and waves. The first type - friction of the body against the water - varies with the speed and shape of the swimmer. This is what you feel and have to pay attention to as a recreational swimmer as it is important at all speeds. For the same body shape it scales linearly with your cross sectional area to the direction of motion and the square of your speed relative to that of the water - just like running or biking through the air. The power required to counteract this resistive force goes as the cube of your speed. It takes a lot of muscle and effort to go just a bit faster.
As you swim there is a pressure difference between the water immediately in front and behind you - the pressure being higher in front. This creates another type of drag and one that becomes increasingly important as you move faster. Most recreational swimmers don't go fast enough for it to dominate, but if you're moving quickly it becomes a real issue in a hurry.
Near the surface of the water you have to plow through the waves. You create your own and have to deal with those of others even in an otherwise perfectly still pool. As you move faster both their amplitude and their wavelength - the peak to peak distance between swells - increase. If you are going fast enough that the wavelength is a bit longer than your height you can get caught in your own trough which is a natural practical speed limit. A taller swimmer will have a longer wavelength to break and has a higher speed limit than someone who is shorter.
The amplitude of the waves you generate can be changed with technique and great progress has been made with computational analysis and the application of newly discovered techniques. Likewise a lot of work has gone into basic swimming technique to supply more thrust.
This wave interaction has an interesting story. If you can swim underwater you don't have to deal with it. A fast freestyle swimmer will stay submerged as long as they can after a start or when they turn. In 2010 an American swimmer broke the world record in the 50 meter backstroke by staying underwater the whole time using a dolphin kick and a few other tricks. In the end he was disqualified and the rules were changed to limit the distance a swimmer can remain submerged. It is important to come as close to this limit if you can if you want to win at the highest levels as wave drag at high speeds can account for more than half the total drag.
World class swimmers tend to have long torsos, very long and powerful arms and relatively short legs with large flippers - er - feet. Mike Phelps and Missy Franklin are both relatively tall with very long torsos and wingspans greater than their heights - they also have great lungs and an insane ability to capacity to use oxygen - a great VO2 max . Both have very large feet and have great arm muscles and big hands. They were made to swim fast. Usain Both is very tall, with a short torso and very long legs, an enormous percentage of white muscle, and a very short achilles tendon. He was made to run fast. Of course, beyond the genetic gifts there is an enormous amount of dedication and excellent training and coaching...
...but at what level of sport are genetic gifts required?
For average k12 and recreational sports I doubt that genetic gifts are required to do well and enjoy yourself. You should do what you enjoy. I've seen really good 5'7" high school basketball players do very well. Perhaps at state tournaments or in very competitive leagues height starts to be necessary, but you can do a lot with hard work and a love of the game. Exceptions may be people who have dramatically different red to white muscle ratios. There are people who just can't jump, but can run forever (that runs in my family) I suspect, for these people as well as for the natural sprinter/jumpers, you will gravitate to sports that seem right to you.
But at the highest level of sport you need everything as well as some luck. Colleen, at 6'7 and extremely long legs and arms, is one of these people. Long limbs are good for some sports, but you pay a price when you need to rotate your body. When she was a pre-teen she really wanted to dive well, but a 6'1 11 year old just can't rotate her body quickly enough. It would be fascinating to make a silhouette of the a composite average of the top few in the world for each sport and create a poster - gymnasts on one end and basketball players on the other. It is remarkable that world class bike riders are about the same height and the same is true of distance runners. But so few of us will compete at these levels that the best advice is undoubtedly what the ad suggests - pick whatever sport you like and -
Just Do It!
1 I tried three or four different materials for a breakable windows the rocket could puncture. Unfortunately materials strong enough to submerge to a satisfying depth kept the rocket inside usually resulting in a delayed rupture with a lot of acrid smoke belching to the surface and a water damaged rocket.
2 I built a little underwater tow track with a couple of pulleys, a crank and a small scale for making measurements. I didn't realize that the airfoils on the models weren't terribly accurate, but I was able to "fly" some of the aircraft and even rig them for climbing and banking by bending little control surfaces I added with a bit of tape.
3 There are four basic forces on an airplane in flight - gravity trying to pull it down, lift counteracting gravity, drag trying to slow the aircraft and thrust from an engine pulling it forward (of course unpowered gliding is possible too and then you just out three forces). If you carefully examine an airfoil the top surface has a concave surface and the bottom surface usually has a flat or cave surface. Air meeting the airfoil either goes above it or below it. The air that travels across the top has a longer path to take and, since the same amount that starts out just in front of the airfoil has to be the same as that just behind it, the air pressure on top is lower and the pressure on the bottom higher. The net result is an upward lift. As the aircraft increases its speed relative to the air it is moving through the lift increases. At some point the lift force exceeds that of gravity and we have flight.
4 Checking the records for the men's 100 meter freestyle the progression has been from 52.9s in 1964 to 4.9s today. The women have gone from 58.9s to 52.1s. Swimming is about four times slower than running for many events so compare this to the 400m track event which has gone from 44.9s to 42.2s for men and 51s to 47.6s for women - a much smaller rate of progression. Technique turns out to be much more important than the exotic and very expensive swimsuits seen during the last Olympics. In sport there is a level where relatively tiny improvements can give an enormous advantage.
5 If you want to motivate a teen to learn a bit about math getting them fascinated by aerodynamics and fluid flow is an outstanding gateway drug. The Navier-Stokes equations are a beautiful way to address fluid dynamics. Non-linear partial differential equations and a bit of fundamental bedrock of mathematical literacy for the physical, and even some of the biological, sciences. A motivated teenager can learn quite a bit if there is a strong motivation.
I love a good granola bar and this chocolate cherry one is a winner. This is good with a scoop of a rich vanilla ice cream on top or just by themselves.
Chocolate Cherry Almond Bars
° 150g (1-2/3 c) rolled oats
° 115g honey (1/3 c) I like Tupelo these days)
° 40g (1/3 c) whole wheat flour
° 1/2 tsp salt
° 50g (about 2 oz) chocolate bar crushed (about 70% cocoa)
° 75g (1/2 c) dried cherries
° 75g (1/2 c) slivered almonds
° 1 tsp good vanilla extract
° 55g (1/4 c) butter (you can use coconut or olive oil)
° 50g (1/4 c) dark brown sugar (I have used 1/2 brown sugar, 1/2 molasses too)
° set oven to 350° F
° combine everything in a large bowl and mix well
° spread onto a baking sheet and pat down until it is about a half inch thick - cover exposed edges with a bit of foil so they don't get too brown
° bake until the top is golden brown - maybe 25 minutes
° cool and cut into whatever bar shape pleases
The second recipe - after all, I didn't post one with the last post, is something I will make in the near future to honor a breakthrough Jean made a few days ago. (isn't it wonderful to celebrate friends like this?). I've made the vanilla and it is one of my best vanillas ever. I've also done the fudge and will make the modification I've suggested. It will be a slam dunk, I'm sure. I'll leave everything in old units as this is from old notes before I began to weigh ingredients. If you don't make your own ice cream try this with a super premium vanilla softened, a good fudge and some peanut butter and peanut butter cups. It should be excellent too:-)
Peanut Butter Chocolate Ribbon Ice Cream
° 1 cup whole milk
° 2/3 cup white sugar
° 2 cups heavy cream in two separate cups - try to get just pasteurized rather than ultrapasteurized if you can
° a bit of salt
° 6 egg yolks from large eggs (odd that large is the standard egg size, isn't it?)
° 2 tsp vanilla extract - highest quality you have
° the scrapings of one vanilla bean
° a couple of handfuls of the smallest peanut butter cups chopped coarsely. I'm guessing about 5 or 6 ounces.
° 1/2 cup white sugar
° 1/3 cup light corn syrup
° 1/2 cup water
° 6 tbl Dutch-process cocoa powder (some of the high end cocoa powers aren't and won't work well here)
° 1/2 tsp vanilla
for the peanut butter ribbon
° 1/3 cup smooth peanut butter (I think the stuff without sugar will be best - but stir it well)
° a bit of whole milk - maybe a couple of tbl
° Heat the milk, sugar, 1 cup heavy cream and a pinch of salt in a sauce pan - just warm it
° in another bowl whisk the egg yolks while slowly adding some of the heated mixture
° As the mixture heats to somewhat warm, put the yolk mixture into the sauce pan
° stir constantly over a medium heat until the mixture thickens. The gold standard is when it coats the spatula - now you have custard
° pour throw a strainer over another bowl you have cleverly pre-positioned and stir in the remaining cup of heavy cream
° stir in the vanilla extract and bean scrapings
° stir it every now and again until it cools and then chill in the fridge for a few hours
now onto the fudge -
° mix the water, sugar, corn syrup and cocoa over a medium heat until bubbles just start to form - then boil for a minute or so stirring constantly and remove from the heat.
° stir in the vanilla extract and let cool. You can pour it into a jar and store it. Make sure it is chilled before you use it!
now for the ice cream making!
° churn freeze the custard mixture as per the instructions of your ice cream machine
° as this happens whisk the milk and peanut butter together
° when the machine begins to slow add the chopped chocolate peanut butter cups and let it run another minute or so.
° move some (a third?) of the ice cream to a storage container and drizzle a third of the fudge and the peanut butter/milk mixture and repeat the process until you have have added all of the layers.
° finish by throwing it in your freezer for a few hours. I suspect I'll break in well before that as I frequently act my shoe size and I happen to be the "adult supervision" here