OT: Off Topic XXI - It's the End of the World As We Know It (and I feel fine)
- Thread starter Ace Rimmer
- Start date
Its never too late to live your dream...
Richard Goodall, 55 year old school janitor (23 years) from Terre Haute, Indiana...
Richard Goodall, 55 year old school janitor (23 years) from Terre Haute, Indiana...
You have my condolences. Losing a parent, especially one you are close to, always leaves a big hole in your life.
On the other hand, you did get to spend a lot of years with your dad. I didn't. Mine passed when I was 26. Remember those years that you did have. I wish I had more.
- Oct 12, 2012
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Unlimited Chequing
Christian Yellow
- Oct 12, 2012
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My wife and I have friends who live in the Tampa area. Hoping and praying they will be ok when Milton hits.
Anglesmith
Setting up the play?
Guilty. I'm definitely not a skating expert, but I'd better know my stuff when it comes to physics.
I was originally imagining skating as the act of pushing perpendicular to the blade, hence my thought about only getting a component of the force. This comes from the thought of a player taking those first strides when starting out where the blade doesn't actually move on the ice. Essentially the running start.
Of course, this stops being applicable as other physics take over when pushing outwards during a stride. I think you have a few things confused in your explanation, though. Let me explain (with a few things you probably already know).
What you are describing with the slippery object is essentially an application of a simple machine: essentially a wedge working in reverse. As you press inwards with a force, the distance you move is tiny, but the force is much greater than the weight of the object. This simple machine multiplies the distance travelled by the object, and the trade-off is that the force it experiences is actually much less than the force with which you squeeze. I'm glad you brought this example up because it is, as you say, exactly the same principle as the skating stride.
The sailboat, though, is the Bernoulli principle. Sailboats move faster while reaching than running because the sail acts exactly like a wing, with the low pressure region created in front pulling the boat forwards.
Now, thinking correctly about the skate moving laterally against the ice, the angle of the skate would determine the mechanical advantage. If you push with a 45 degree angle, you would not expect any difference between the force pushing outwards and the force that the ice then enacts on the blade forwards. So this is only going to be more efficient than running if we can push sideways harder than we can push backwards. I'm not convinced that that is true. Pushing backwards while starting a sprint and leaning forwards is essentially using all of the biggest muscles in our core and legs to simply unbend all the joints. I can't see a sideways push being stronger.
If the skate is angled more in line with the pushing direction, then yes, there would be force amplification. The force you apply laterally results in a multiplied force forwards, just like driving a wedge into wood. But the tradeoff is in distance: the distance you push the skate outwards results in much less distance travelled forwards; the ratio is ideally the same as the force ratio. In addition, the force you can push with is limited by the resistance of the ice. Even if you move your skate outwards as fast as the resistive force and your own bodily mechanics allow, you aren't going to see a huge forward acceleration: what is more likely is that you see a decent forward acceleration with much less force required than if you were pushing backwards.
If the skate is angled more in line with the skating direction, you get amplification of distance, but at the tradeoff of needing to push much harder than the accelerating force that results. This ends up meaning that you can only do this fairly slowly (and I'm pretty sure this isn't what is done by most skaters).
So I think it's misleading to suggest that a skating stride creates more force than a running stride. I think it would be much more correct to say that a skating stride requires less force than a running stride. At the end of the day, the work put into a stride by either a runner or a skater gets converted into kinetic energy. I would still maintain that this is more efficient for the runner early on: from a physics perspective, the skating stride requires the skate to slide through the ice, which incurs energy losses due to friction.
I think your taking the wrong point from the sailing example, not as much as the method of propulsion of the sail moving the boat but how sailing closer to between 45° to 90° to the wind actually provides a lot more velocity pending on the sail being large enough to convert the force necessary to make it work. But to be honest my non-existent sailing terminology is holding me back from knowing for sure.
Think of it as a triangle with a x axis being 1” and the y axis being 90”. If I slide my hand up along the x axis, starting at the hypotenuse tip along the y axis, for every 1” I move my hand forward it moves 90” laterally. If my hand was incapable of moving along the x axis while the triangle incapable of moving along the y, that means the triangle would move laterally 90” every 1” I move my hand. It would take a lot more force to move it this distance rather than if the numbers were inverse, but the rate of return of distance is much larger the steeper the angle. Skating doesn’t go this extreme, but follows the same principle. While running, your speed is the literal speed you can move your legs. Whereas with skating, your speed is decided by the amount of angular force your capable of applying. This formula does get aided by the fact that while you aren’t directly applying said force, you will maintain speed while skating rather than running for obvious friction reasons.
For demonstration look at these two record runs.
For reference, Usaine Bolt was traveling at 45km/h, where as Kjeld Nuis hit 103 km/h (obviously getting to almost ignore friction caused by wind resistance). The key difference is the angle of force applied. For every 1 meter Usaine bolts feet move, he propels forward that exact distance, whereas Kjeld gets the mechanical advantage of his stride being within the 90° to 135° from his direction he’s travelling. Look at the difference between Usain’s foot speed compared to Kjeld’s to really display the mechanical advantage. While Kjeld’s feet are distinctly moving slower, he is still capable of providing acceleration at speeds passed 90 km/h. That is quite impossible for Usain, as no human being is capable of moving there feet at such a speed to cause this even with wind resistance removed.
It’s this exact reason skaters widen their stance as their speed increases. The acceleration provided by a wide stride is limited because as you pointed out, the amount of force required to achieve it would be extreme. However, as you approach top speeds, widening the stride makes it possible to move much faster than you’re capable of moving your feet. So while acceleration would be limited, peak velocity would me much higher. The same as the advantage gained by having a bike with gears. While accelerating in 6th gear is a daunting task, if you start in first gear
(No angle smaller than 135° to forward direction), then slowly raise gears (build up to angles more perpendicular to the forward direction), you lose acceleration but gain top speed.
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Anglesmith
Setting up the play?
I think we're on the same page. At the end of the response though is the key: my argument was about initial acceleration from rest exclusively. I was acknowledging that the skater absolutely has an easier time maintaining and a huge advantage in increasing their speed further once already going.
At the point of acceleration from rest, the difference would be insanely close to one to one. The skater has a slight disadvantage due to the out turn of the ankle to utilize the edge of the blade which would shift slightly away from the main muscle groups, but almost immediately can start utilizing mechanical advantages that a sprinter can not. This is displayed by the 100m sprint record being 9.58s, while skatings record (inline, not ice) is 9.68s. The only man ever to beat the inline skating record is Usaine Bolt, which is insane considering the pool of sprinters in the world compared to the pool of inline skaters. The sprinter would have the advantage in the first two to three steps, but a skater would rapidly get the upper hand in velocity reached. It would be an interesting study to see at what distance an average speed skater is able to hit speeds higher than the average sprinter can, because out of the block a sprinter has the advantage but the records aren’t nearly as far apart at a distance of 100m as you’d expect.
Edit: Did more digging, at the world roller speed skating championships in 2015, the top 5 averaged for 9.906s for 100m. In the Rio Olympics the very next year, the top 5 100m runners averaged 9.8906s. The difference is extremely close.
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- Oct 12, 2012
- 57,812
- 9,850
