Saturday, April 30, 2011
LA Skate Film Festival 2010: Nominees Announced
LA Skate Film Festival 2010: Nominees Announced
The LA Skate Film Festival has announced the nominees for its 1st annual event that will be held August 31st & September 1st, 2010, in downtown LA.Source: NEWS/Skateboarding/LA_Skate_Film_Festival_2010_Nominees_Preview_0762.htm
King of Wake Releases 2010 Schedule
King of Wake Releases 2010 Schedule
Get ready for the world's best pro wakeboarding series, which kicks off this April. King of Wake has announced where and when the most elite pro wakeboarders will compete for the crown.Source: NEWS/Wakeboarding/King_of_Wake_Releases_2010_Schedule_0617.htm
The North Face Freeskiing World Tour Heads to South America
The North Face Freeskiing World Tour Heads to South America
The world�s best freeskiers are on their way to South America for the first few stops of the Freeskiing World Tour. These snowy mountains are the perfect place to fight for the event title, World Tour points, and a cash purse.Source: NEWS/Freeskiing/The_North_Face_Freeskiing_World_Tour_Argentina_Preview_0749.htm
Kitesurf
MAKING OZ posted a photo:
Kitesurfing en Guardamar del Segura.
Patagonian Expedition Race 2009: Adventure in Chile
Patagonian Expedition Race 2009: Adventure in Chile
Adventure racing athletes from all over the world experienced life changing situations whilst crossing hundreds of kilometres of wilderness. The Patagonian Expedition Race tested wills, expanded horizons and broke down barriers.Source: NEWS/Extreme_Sports/Patagonian_Expedition_Race_2009_0366.htm
Whitewater kayaking Whitewater canoeing Free diving Scuba diving
2011 Street League Skateboarding Series Makes First Stop In Seattle, Washington
2011 Street League Skateboarding Series Makes First Stop In Seattle, Washington
Street League Skateboarding, the premier professional street skateboarding series worldwide, has announced its exciting return by releasing the 2011 League schedule.Source: NEWS/Skateboarding/Street_League_Skateboarding_Series_2011_Preview_0853.htm
Mastercraft Pro Wakeboard Tour 2010 Fantasy Game
Mastercraft Pro Wakeboard Tour 2010 Fantasy Game
$2,000 in prize money will be up for grabs this year in the 2010 MasterCraft Pro Wakeboard Tour fantasy game. Earn points for your fantasy team as the pro riders compete on tour.Source: NEWS/Wakeboarding/Mastercraft_Pro_Wakeboard_Tour_2010_Orlando_Preview_0684.htm
Friday, April 29, 2011
eXtreme Sports Physics Gift List, Part 2
More holiday gift ideas for eXtreme sports addicts.
(In case you missed it, I posted five other ideas a little bit ago in eXtreme Sports Physics Gift List, Part 1.)
Hang Time!
When you catch air, you're in freefall. Another way to put it is that you're in a very low orbit that intersects with the ground. Either way, you're briefly weightless.If you were to strap an accelerometer to your leg to measure the forces on your body, you would see it go to zero when you're in the air. If only there was some way to hook an accelerometer to a timer, you'd know how much hang time you pulled . . .
Actually, there are at least two companies making timers to record the duration of your monster airs. My favorite is the AirPod, but you might want to look into the slightly glossier (and pricier) HangTimer. Personally, I'm all about the data, bling means nothing to me. So I'll save a couple bucks and go with the AirPod.
I'm guessing a lot of folks will be disappointed to find out how little time they spend airborne. On the other hand, once you come to terms with the fact that humans really weren't meant to fly and you learn to appreciate the few precious seconds during each run that you get to enjoy free of our earthly bonds, you'll realize that devices like the AirPod and HangTimer are excellent tools for evaluating and perfecting your aerial skills.
AirPod - fly, be free, take data
$59 and up
In Search of a Fast Frame Rate
If you're a decent photographer, you'll always be a welcome addition in any eXtreme sports road trip. You might even get a free meal or two along the way.As a rule, eXtreme sports junkies love to see themselves immortalized in high resolution action pics. One of the tricks to getting the shot is making sure you have a camera that can take lots of images very quickly. Pros spend multi-thousands for high frame rates. But you can do almost as well with a few cameras that slip in at just about a thousand bucks.
After using several digital cameras that deliver 2 to 3 frames a second, I found that I was going to need something faster, particularly in the skatepark and on the slopes. My budget limited me to the 5 frame per second and 8.2 megapixel Canon EOS 30D, which retails (with one lens included) at Amazon for $1025. Here's an example of one shot I captured of my son grinding the coping in a 10 foot deep pool at our local skatepark.In order to get this shot, I actually took 6 pictures, as you can see from this sequence. The one I wanted is number 4.
The high frame rate is good for more than just photos, it also helps me do a bit of physics calculating. For instance, from these shots I can tell that my son traveled about 2 meters in the second that it took to fire off 5 frames, which means he was moving at 2 meters a second. The pool curvature is about 2.5 meters in radius at this point, so he was experiencing a horizontal g-force of about 1/6 the force of gravity. That's what was pinning him to the board as he carved around the pool. Cool, isn't it?
The 30D's older brother, the EOS 20D, has the same frame rate and resolution, but a smaller buffer, so you can't shoot as many shots in a row before stopping to let the electronics catch up.
If you're made of money, you can step up to the 10 megapixel EOS 40D at 6.5 frames per second. (The last time I checked, the EOS Rebels were all limited to 3 frames per second, so they don't make my cut.)
As far as I know, the Canon EOS line offers the fastest frame rate among the $1k cameras. If I find anything faster, I'll let you know.
Canon EOS SLRs
Just hold the button down, chances are at least one of those dozens of shots is going to be a keeper
$974 and up
Eye Witness
There's nothing like watching a crash from the first person perspective, and the best way to do that is with a helmet cam. (I'll post my own favorite crash as soon as I can get it downloaded from my son's PC.)
You can spend a bundle for a high tech, waterproof, shock proof helmet camera, or you can save money the way I did.
I bought a $99 camera that records straight to flash memory. Then I sometimes tucked it under the strap for my snow goggles (be sure to loop the camera's wrist lanyard around your goggle straps), velcroed it to my leading leg, or duct taped it to my skate helmet.It makes for cool, low budget follow shots and gives a realistic view of what it's like to cruise down a mountain or thread your way through a half pipe. The crashes are the most fun to watch, complete with brutal crunching sounds and groans of pain. Just don't show them to your parents or significant others until a season or two has passed. Otherwise they'll beg you to stay off the slopes, rails, ramps, tracks, or whatever else you ride.
Helmet Cams - first person adventure and pain
$79 and up
First Aid - it's the best kind
Despite taking things to the edge, few extreme sports injuries involve compound fractures or head trauma. A few bumps, bruises and abrasions are the much more likely results of any given adventure. But the recent epidemic of coverage in the media of staph infections makes it clear that even minor scrapes need quick attention. Besides, you don't what your favorite eXtreme athlete staining his or her stylin' new jeans or jacket with unsightly blood stains.I used to load up my backpack with a few Band-Aids and sterile pads, but it's a lot easier to just grab a prepackaged first aid kit and toss it in the trunk with the rest of my gear. REI offers a range of kits, from tiny sets that slip in the glove box to fairly comprehensive packs that include everything you need for most injuries, including a copy of "The Wilderness First Aid Manual."
First Aid Kits - 'cause your mom won't always be nearby to kiss the boo boo
$28 and up
Surfrider Gift Membership
As the nigh-invulnerable superhero "The Tick" once said after being asked if he could destroy the Earth "Ye Gods! I hope not! That's where I keep all my STUFF!"The Earth is a fragile place, and even if the Tick is no threat, without the work of groups like the Surfrider Foundation, you're likely to eventually lose all your stuff - and a lot more. In their own words . . .
The Surfrider Foundation is a non-profit grassroots organization dedicated to the protection and enjoyment of our world?s oceans, waves and beaches. Founded in 1984 by a handful of visionary surfers in Malibu, California, the Surfrider Foundation now maintains over 50,000 members and 80 chapters worldwide.
Even if you're not into eXtreme water sports, remember that most of this precious planet is ocean, and you can't have a healthy Earth without clean water.
So join Surfrider this year or give someone a gift membership - your great grandkids will thank you for it, and you get a cool bumper sticker.
Surfrider Gift Membership
$25
Why is Snow so Slippery?
Snow sports are a blast. I prefer snowboarding, but I would never miss out on a toboggan ride or a turn on one of those old fashioned snow saucers (What genius conceived of those anyway? Is there anything more insane that cruising down a hill on a disk with no obvious way to steer or stop? Of course, I love it anyway.) As embarrassing as it is, I've even been known to to ride an inner tube now and then.The key to all those sports - as well as skiing, snowlerblades, ski bikes, and cafeteria lunch trays - is that things slide well on snow. You could leave it at that and simply go outside to have fun, but I just had to know a bit more.
If you hunt around, you'll see that there are at least two possible reasons why snow is slippery. One common explanation is that the melting point of ice rises as you squeeze it. Water ice is unusual in that way. This could explain why ice skates work. When you stand on skates, it creates very high pressures under the sharp blades. The pressure raises the melting point of the ice until it creates a thin layer of water, which is very slippery. (This is, however, not a universally accepted explanation.)
Pressure might work for ice skaters, but it's not much help for sleds, skis, snowboards, or any other device that slides on a large, flat surface. Because your weight is distributed over a big board, the pressures are very low. At best, you might raise the melting point of the ice by a degree or so, but if the temperature of the air and snow outside is more than a few degrees below freezing, you won't actually melt any snow with pressure.
Another possibility I've heard on occasion is that the friction of the board sliding on the snow creates heat, which melts some of the snow and creates a thin lubricating layer of water. Now, this explanation sounded just absurd to me. But I didn't want to dismiss it until a estimated just how much heating you might get from snowboarding down a hill.
You know what? I was stunned -- STUNNED -- to find out that cruising down a hill creates lots of heat. At a relatively modest 36 kilometers an hour (22 mph) down an equally modest hill (imagine a 15 degree slope or so), someone about my size (75 kilograms) creates about 300 watts of heat power due to friction between the snowboard and the snow. That's three times as much power as put out by a typical light bulb. If you've ever touched a lit incandescent bulb, you know that's hot. Theoretically, friction could heat the bottom of the board by nearly 40 degrees Celsius (about 100 degrees Fahrenheit)! In the real world, the bottom of your board will never get that hot. It will only warm up to the point that it melts the snow. It takes energy to melt snow, and the melting ends up using the energy that would heat your board to any higher temperature than 0 degrees C (32 degrees Fahrenheit).
But suppose you were snowboarding on a day when temperatures went as low as at -40 degrees C, even moving slowly would generate enough heat from friction to melt the snow and provide a very thin layer of water for you to slide on. (Of course, -40 C is just about the lowest temperature ever recorded in Alaska, so you'd probably get an awful case of frostbite before you got to the top of the lift.)
So there you have it - it's friction, not pressure, that melts snow below your board and let's you whiz down the hill at a breakneck pace. Wacky.
For those of you who like the details, the math that led me to this conclusion is below.
The Math and Physics
You can change the parameters of the problem to model any sliding sport you like, but I'm using a snowboard in my analysis.
The first thing to do is figure out how much work is done when you slide on a snowboard. Work is defined as force times distance. Specifically, we're interested in the frictional force multiplied by the distance traveled.
The force of friction is just the force pushing the snowboard down onto the snow multiplied by the coefficient of friction (u).
Because the snowboard is moving downhill, the force pushing against the snow due to the mass of the snowboard and rider is reduced by the cosine of the hill slope.
Friction force = m g u cosine(theta)
m = rider's mass (I'm using 75 kilograms)
g = acceleration due to gravity (0.8 meters per second squared)
u = coefficient of friction for a waxed board sliding on snow (about 0.04, according to Wikipedia)
theta = slope of the hill (I'm using a modest 15 degrees)
If you multiply this by the distance traveled on the hill, you get the total energy expended on the trip. If instead, you multiply the force by the velocity of the snowboard, you get the work per unit time. That's the same as the power (watts in SI units).
Power = m g u cosine(theta)* v
v = velocity (for this problem, I'm using 10 meters/second, which is about 36 kph, or 22.5 mph)
Plug all that in, and you find a power output of about 284 watts to slide down the hill.
The equation for heat conduction through a slab of material (such as a snowboard deck) is
Power = dQ/dt = k A (T2-T1)/L
k = thermal conductivity (about 0.25 Watts/(meters*degrees Kelvin))
A = area of board touching the ground (about .25 square meters for a typical board)
T2 = temperature on the hot side of the board (in Kelvin)
T1 = the temperature on the cold side of the board
L = the thickness of the board (I'm using one centimeter, 0.01 meters)
When I rearrange this to solve for the temperature difference between the two sides of the board (T2-T1) and plug in the numbers, I get temperature difference of about45 degrees.
As I mentioned above, that's the maximum temperature difference between the two sides, but the hot side should never get above the freezing point of water because the heat generated by friction would have to melt all the snow before it could lead to higher temperatures. That's because of the phase transition from ice to water that occurs at the freezing point (It's the same reason that water with any ice in it at all will have a temperature of exactly 0 degrees Celsius. You can confirm this by putting a pot of snow on the stove and turning up the heat. The temperature will rise to 0 degrees C and stay there until all the snow is melted.).
So, if you're out snowboarding when the air temperature (and top of your board) are at -5 degrees Celsius, the temperature of the bottom of your board be about 0 degrees Celsius when you're moving along at 10 meters/second. In fact, it will always be at about 0 degrees Celsius if you're moving at almost any reasonable speed, and there will be a very thin layer of water under it due to all the frictional energy you're generating by sliding down the mountain.
Source: http://feedproxy.google.com/~r/blogspot/uUCU/~3/98TqO5Qa59k/why-is-snow-so-slippery.html
Jossi Wells is AFP Overall World Champion For 2010
Jossi Wells is AFP Overall World Champion For 2010
Unlike other performers, Jossi Wells rocks all three disciplines in freeskiing competitions. His AFP halfpipe rankings are off the chart and he continues to rack up the titles in the 2010 season.Source: NEWS/Freeskiing/Jossi_Wells_is_AFP_Overall_World_Champion_Results_0636.htm
Red Bull X-Fighters 2010: Battersea Power Station In London
Red Bull X-Fighters 2010: Battersea Power Station In London
New Zealand�s Levi Sherwood recharged London�s iconic Battersea Power Station on Saturday as he won the fifth stop of the Red Bull X-Fighters World Tour 2010 in the British capital.Source: NEWS/Biking/Red_Bull_X-Fighters_Battersea_Power_Station_London_Results_0755.htm
Nine Knights 2010: The Knights Are Ready
Nine Knights 2010: The Knights Are Ready
The line up for the most exciting freeski event of the year is set. The Nine Knights is anything but the usual freeski competition and on the 24th of April they will leap through the snow, battling for fame and glory.Mogul's Happen
(Oops, I made a calculation error. It turns out that moguls should form at much shallower slopes than I initially estimated. See the Mathy Bits section for an explanation. Thanks for catching the mistake, MC!)
People seem to have a love-hate relationship with moguls - they're lots of fun if your timing and knees are good. They can be a real pain if you prefer a more casual descent down the slopes and you happen to get stuck above a gnarly mogul field.
I've hit the moguls on occasion, and regretted it more than once. I can recall sitting on the snow nursing my hyper-extended knee and wondering why on earth they make these things.
After looking into the science behind them, I found out that no one actually makes moguls at all, at least not on purpose. Moguls happen all by themselves, with a little unintentional help from snowboarders and skiers.
Moguls are an example of something called a self-organizing structure. All you need is a snow-covered slope and some folks to slide down it, and soon they will push the snow into lumps that form stunningly organized moguls. There's no way to stop it from happening. All you can do is run over the slope with a groomer to cut the things down from time to time.
Typically, self-organizing structures arise whenever patterns are formed as a result of many simple parts that follow a few basic rules. Common examples you've probably seen include crystals (salt, diamond, and snowflakes to name just a few), sand dunes, ocean waves, flocking birds, schooling fish, and the patterns in bubbles rising through a glass of champagne.
It's hard to predict in advance how the rules might lead to patterns. The best we can do, in most cases, is to look at the pretty structures and then work backward to figure out what rules might have made it happen. Even then, it's not always clear what the underlying rules really are, so physicists sometimes make up rules that seem to explain things reasonably well. This is what we call empirical science.
As far as I can tell from researching the scientific journals, nobody truly understands moguls. That hasn't stopped them from coming up with theoretical models that work adequately, even if they're probably not completely true.
One of the scientists who has looked into moguls is Regis University computer science professor and extreme skier Dave Bahr. He's made time lapse movies of moguls and shown - now get this - that moguls slowly migrate up hill over the course of a winter. Check out his videos. They're eerie. It's like the moguls are alive.
Bahr explains how this happens with a little cartoon, and has promised to write a formal paper about it eventually. Basically, as you make your way through the moguls, you end up scraping some of the snow from the downhill side of one bump and depositing it on the uphill side of the next one down. So even though you're pushing snow downhill, the moguls themselves move up.
There isn't much else in the scientific literature about moguls, but a recent physics paper analyzing the washboard ripples that often form on dirt roads seems to offer some insight into bumps on the slopes. The physicists who wrote the paper filled a tray with sand, and then ran a wheel across it to see when and how ripples would form. 
And ripples almost always developed - unless they rotated the tray very, very slowly. They concluded that all dirt and gravel roads would develop washboard ripples if traffic moved any faster than a few miles an hour. That is, you would have to keep traffic to speeds slower than the rate at which most people walk if you want to stop ripples from forming on your dirt driveway. Check out this short video showing their experiment in action.
The thing that makes this research relevant to snowboarding and skiing is that they also tried dragging a non-rotating square block along the sand. That too caused ripples to form. When you think about it, it's a lot like what you're doing when you slide down the slopes on a board or skis. Mogul fields are essentially giant washboard roads that are created by snowboard and ski traffic rather than cars and trucks.
If you apply the theory behind road ripples to moguls on snow, it turns out that moguls won't form if the slope is mellow enough. It has to be VERY mellow though. If I did the math right (you can check it in the mathy bits below), only slopes with less than 7 degrees 2.3 degrees incline (about a 12% 4% grade) will stay mogul-free on their own - that's bunny slope territory darned near flat! Anything steeper will have to be groomed to keep the moguls down.
The bottom line is there's no one to blame for moguls but ourselves and physics. So you either have to learn to ride them, or stick to groomed trails, or (best and hardest of all) find a fresh back bowl where the snow is still untouched and nobody's had a chance to pile up those bumps.
The Mathy Bits
(As you will see from the portions crossed out, I initially calculated that moguls form on slopes steeper than 7 degrees. But after someone pointed out that I seemed to have made a math error, I found that the actual answer is probably closer to 2.3 degrees. It turns out that I put the factor for the snowboard width in the numerator rather than the denominator at one point when I made the substitution for v^2. I don't show all these details because it's hard to do math in the Blogger interface. But if you want to talk about the details, drop me a note at "buzzskyline at gmail.com".)
In their Physical Review Letters paper about washboard roads, physicists Nicolas Taberlet, Stephen W. Morris, and Jim N. McElwaine suggested that there's something called the Froude number, which predicts when ripples will form on a dirt or gravel road. They write the Froude number equation essentially like this
Fr=(v^2/g)*(p*w/m)
v is velocity
g is the acceleration due to gravity
p is the density of the sand (or snow)
m is the mass of the wheel (or snowboarder)
w is the width of the wheel (or snowboard)
Whenever Fr is greater than one, washboard ripples form. Of course, the only thing that isn't constant in the equation is v, which is just the speed of the wheel over the sand. All the rest of the components are fixed.
It's pretty clear that all you need to do to keep Fr below one is to slow down.
To apply this to snow, I estimated that the density of packed snow is about half the density of liquid water (500 kg per cubic meter), the mass of the average snowboarder is about 70 kg, and the width of the average snowboard is about 20 centimeters.
If you recall from my post about Speed Snowboarding, you can solve for the terminal velocity of a snowboarder pretty easily by rearranging this equation
m*g*sin(theta)= u*m*g*cos(theta) + (p*A*Cd*v^2)/2
The terminal velocity is the speed limit on the hill. Not that it's illegal to speed at the slopes, it's just that physics won't let you go faster than the terminal velocity.
If I plug the terminal velocity from the Speed Snowboarding post in the equation for the Froude number, I can see that Fr<1 whenever the angle theta is less than about7 degrees 2.3 degrees.
You should bear in mind that the washboard road paper uses some pretty shaky logic to come up with their Froude number, and that I am just blindly applying their calculation to snow, so take this all with a grain of salt.
Still, it seems reasonable that there should be some slope that's too mild for moguls to form. Although I don't know if anyone has tested it, I bet you'd never see moguls on a bunny slope with a7 degree 2.3 degree or less drop, even if it were never groomed.
On the other hand, even a gentle beginner slope would be steep enough to develop moguls if left ungroomed for long.
People seem to have a love-hate relationship with moguls - they're lots of fun if your timing and knees are good. They can be a real pain if you prefer a more casual descent down the slopes and you happen to get stuck above a gnarly mogul field.I've hit the moguls on occasion, and regretted it more than once. I can recall sitting on the snow nursing my hyper-extended knee and wondering why on earth they make these things.
After looking into the science behind them, I found out that no one actually makes moguls at all, at least not on purpose. Moguls happen all by themselves, with a little unintentional help from snowboarders and skiers.
Moguls are an example of something called a self-organizing structure. All you need is a snow-covered slope and some folks to slide down it, and soon they will push the snow into lumps that form stunningly organized moguls. There's no way to stop it from happening. All you can do is run over the slope with a groomer to cut the things down from time to time.
Typically, self-organizing structures arise whenever patterns are formed as a result of many simple parts that follow a few basic rules. Common examples you've probably seen include crystals (salt, diamond, and snowflakes to name just a few), sand dunes, ocean waves, flocking birds, schooling fish, and the patterns in bubbles rising through a glass of champagne.It's hard to predict in advance how the rules might lead to patterns. The best we can do, in most cases, is to look at the pretty structures and then work backward to figure out what rules might have made it happen. Even then, it's not always clear what the underlying rules really are, so physicists sometimes make up rules that seem to explain things reasonably well. This is what we call empirical science.
As far as I can tell from researching the scientific journals, nobody truly understands moguls. That hasn't stopped them from coming up with theoretical models that work adequately, even if they're probably not completely true.
One of the scientists who has looked into moguls is Regis University computer science professor and extreme skier Dave Bahr. He's made time lapse movies of moguls and shown - now get this - that moguls slowly migrate up hill over the course of a winter. Check out his videos. They're eerie. It's like the moguls are alive.
Bahr explains how this happens with a little cartoon, and has promised to write a formal paper about it eventually. Basically, as you make your way through the moguls, you end up scraping some of the snow from the downhill side of one bump and depositing it on the uphill side of the next one down. So even though you're pushing snow downhill, the moguls themselves move up.
There isn't much else in the scientific literature about moguls, but a recent physics paper analyzing the washboard ripples that often form on dirt roads seems to offer some insight into bumps on the slopes. The physicists who wrote the paper filled a tray with sand, and then ran a wheel across it to see when and how ripples would form. And ripples almost always developed - unless they rotated the tray very, very slowly. They concluded that all dirt and gravel roads would develop washboard ripples if traffic moved any faster than a few miles an hour. That is, you would have to keep traffic to speeds slower than the rate at which most people walk if you want to stop ripples from forming on your dirt driveway. Check out this short video showing their experiment in action.The thing that makes this research relevant to snowboarding and skiing is that they also tried dragging a non-rotating square block along the sand. That too caused ripples to form. When you think about it, it's a lot like what you're doing when you slide down the slopes on a board or skis. Mogul fields are essentially giant washboard roads that are created by snowboard and ski traffic rather than cars and trucks.
If you apply the theory behind road ripples to moguls on snow, it turns out that moguls won't form if the slope is mellow enough. It has to be VERY mellow though. If I did the math right (you can check it in the mathy bits below), only slopes with less than The bottom line is there's no one to blame for moguls but ourselves and physics. So you either have to learn to ride them, or stick to groomed trails, or (best and hardest of all) find a fresh back bowl where the snow is still untouched and nobody's had a chance to pile up those bumps.
The Mathy Bits
(As you will see from the portions crossed out, I initially calculated that moguls form on slopes steeper than 7 degrees. But after someone pointed out that I seemed to have made a math error, I found that the actual answer is probably closer to 2.3 degrees. It turns out that I put the factor for the snowboard width in the numerator rather than the denominator at one point when I made the substitution for v^2. I don't show all these details because it's hard to do math in the Blogger interface. But if you want to talk about the details, drop me a note at "buzzskyline at gmail.com".)
In their Physical Review Letters paper about washboard roads, physicists Nicolas Taberlet, Stephen W. Morris, and Jim N. McElwaine suggested that there's something called the Froude number, which predicts when ripples will form on a dirt or gravel road. They write the Froude number equation essentially like this
Fr=(v^2/g)*(p*w/m)
v is velocity
g is the acceleration due to gravity
p is the density of the sand (or snow)
m is the mass of the wheel (or snowboarder)
w is the width of the wheel (or snowboard)
Whenever Fr is greater than one, washboard ripples form. Of course, the only thing that isn't constant in the equation is v, which is just the speed of the wheel over the sand. All the rest of the components are fixed.
It's pretty clear that all you need to do to keep Fr below one is to slow down.
To apply this to snow, I estimated that the density of packed snow is about half the density of liquid water (500 kg per cubic meter), the mass of the average snowboarder is about 70 kg, and the width of the average snowboard is about 20 centimeters.
If you recall from my post about Speed Snowboarding, you can solve for the terminal velocity of a snowboarder pretty easily by rearranging this equation
m*g*sin(theta)= u*m*g*cos(theta) + (p*A*Cd*v^2)/2
The terminal velocity is the speed limit on the hill. Not that it's illegal to speed at the slopes, it's just that physics won't let you go faster than the terminal velocity.
If I plug the terminal velocity from the Speed Snowboarding post in the equation for the Froude number, I can see that Fr<1 whenever the angle theta is less than about
You should bear in mind that the washboard road paper uses some pretty shaky logic to come up with their Froude number, and that I am just blindly applying their calculation to snow, so take this all with a grain of salt.
Still, it seems reasonable that there should be some slope that's too mild for moguls to form. Although I don't know if anyone has tested it, I bet you'd never see moguls on a bunny slope with a
On the other hand, even a gentle beginner slope would be steep enough to develop moguls if left ungroomed for long.
Source: http://feedproxy.google.com/~r/blogspot/uUCU/~3/KSrkkByVuU0/moguls-happen.html
Elias Amb�hl Rocks The Fridge Festival Big Air In Budapest
Elias Amb�hl Rocks The Fridge Festival Big Air In Budapest
Budapest hosted the first ever major freeski event in Eastern Europe with the Fridge Festival last weekend. This event is an exciting preview of the superior freeskiing that the upcoming winter season has in store.Source: NEWS/Freeskiing/Fridge_Festival_Big_Air_2010_Budapest_Results_0809.htm
Think Pre-Lockdown Interview
Moments before being locked inside Double Rock, Josh Matthews and Lee Yankou sat down to answer a few questions.
Source: http://broadbandsports.com/node/48206
Alessandra Nanni Alex Broskow Andre Englehart Andreas Trefzer
Thursday, April 28, 2011
Getting a Goat?s View of Sardinia?s East Coast
The best way to see the ruggedly gorgeous coast of the Orosei Gulf is by hiking a little known trail, lined with limestone cliffs and isolated beaches.Source: http://travel.nytimes.com/2009/02/22/travel/22explorer.html?partner=rssnyt&emc=rss
Trip Report: Chile 2010
"Still buzzing from the excitement of the Green Race, Gareth Tate and Laura Farrell head south for a month of kayaking in Central Chile. With fast paced footage from a newly discovered multi-day trip in the upper Nuble Valley (first D; Jon Clark), a break down of the world class "Throat Of The Devil" drop on the Rio Claro, and a highlight reel of two of the Pucon areas classic local runs, the Rio Nevados and the Rio Palguin. Follow their journey of traveling over 5,000 miles with their kayaks to run a some of the best creeks and waterfalls of Chile. "
Shot in November 2010.
Paddlers:
Gareth Tate
Laura Farrell
Jon Clark
Matias Nunez
Nate Mac
Evan Garcia
David Fussili
Fred Norquist
Jarred Seiler
Nicole Mansfield
Kurt Casey
Gringo
Momo
Andre
Video & Edit: Gareth Tate
Shot with: Canon Vixia / GoPro Hero HD
Special thanks to:
astralbuoyancy.com/
dagger.com/pages/index/homepage
gopro.com/
Cast: 7 Finger media
The History of Snowboarding
This is all there is to it. Pay close attention - this stuff will be on the quiz.
Source: http://feedproxy.google.com/~r/blogspot/uUCU/~3/-eNSa2s9hos/history-of-snowboarding.html
The History of Snowboarding
This is all there is to it. Pay close attention - this stuff will be on the quiz.
Source: http://feedproxy.google.com/~r/blogspot/uUCU/~3/-eNSa2s9hos/history-of-snowboarding.html
Wake the Line 2010: German Wakeboarders Dominate In Cologne
Wake the Line 2010: German Wakeboarders Dominate In Cologne
12,000 visitors followed the Wake the Line Contest on the 4th of July in Cologne. At the world's largest Wakeboard Obstacle Only Event the German riders were there to impress.Source: NEWS/Wakeboarding/Wake_the_Line_Cologne_Results_0730.htm
Classics: Cairo Foster Real to Reel
It's simple: Amazing skaters ride for Real and they put out some of the best parts ever. Since Day One premieres this Thursday. Here's Cairo from 2001.
Twelve Productions - South Island Heli-Kayaking.
Here's a little edit from our west coast helicopter kayaking trip in New Zealand.
Bruce Dando the local pilot flew us up the Hokitika, Arahura, Kokatahi and Whitcomb rivers...
Paddlers from NZ, USA,NED,ARG etc... gathered around to make it a sick trip.
Follow us on Facebook: facebook.com/twelveproductions
twelve-productions.com
Cast: Twelve Productions
Wednesday, April 27, 2011
Point Of No Return
Its been a long time coming.
Winter 2010 Boating from the heart of The Valley, Africa and North Wales.
Featuring Matty,s Uganda swim and the high water decent of Pont y Pant on the Lledr that was so widely discused on the Forum website.
Cast: Matty Nicholas
2011 Street League Skateboarding Series Makes First Stop In Seattle, Washington
2011 Street League Skateboarding Series Makes First Stop In Seattle, Washington
Street League Skateboarding, the premier professional street skateboarding series worldwide, has announced its exciting return by releasing the 2011 League schedule.Source: NEWS/Skateboarding/Street_League_Skateboarding_Series_2011_Preview_0853.htm
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