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Author Topic: Ice skating, speed and falling over.  (Read 8362 times)

paul.fr

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Ice skating, speed and falling over.
« on: 25/08/2007 17:47:33 »
I am rubbish at ice skating. when going slow like a girlie so i don't fall over i wobble all over the place, yet when i get some speed up i look just like an olympic skater!

Why is this?


 

Offline DoctorBeaver

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Ice skating, speed and falling over.
« Reply #1 on: 25/08/2007 21:52:12 »
I am rubbish at ice skating. when going slow like a girlie so i don't fall over i wobble all over the place, yet when i get some speed up i look just like an olympic skater!

Why is this?

Jane Torville?  :D

It's the same principle as going at different speeds on a bike. Bikes are very unstable at low speeds but get more stable as you accelerate (up to a point).

Someone did explain it to me once. I seem to remember it's something to do with energy transfer - but I'm probably wrong.
« Last Edit: 25/08/2007 21:54:52 by DoctorBeaver »
 

Offline Karen W.

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Ice skating, speed and falling over.
« Reply #2 on: 25/08/2007 23:45:16 »
I am a lousy roller skater I have never even seen an ice rink in my life. They said they used to have one before I was born nearly 5o years ago! LOL

I hate falling down. And usually took out my partner in the process!
I think balance is better once you get into a rhythum...
 

Offline syhprum

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Ice skating, speed and falling over.
« Reply #3 on: 26/08/2007 09:42:38 »
As we are adapted to walking upright we have a built in system for keeping our centre of gravity directly above our feet or the point of contact of our bicycle tires or ice skates with the ground (or ice) as the case may be.
when we ride a bicycle we have to move this point of contact from side to side by moving the handlebars which is easy when we are moving forward at a reasonable pace but the slower we go the more sluggish the responce becomes until when we are stationary then we can do nothing.
The same applies to ice skating only the requisite sideways movement is generated by twisting our ankles.
Of course not only is a sideways motion needed but a backwards and forwards one too this is easy on a bicycle or on fairly long feet or skates but hellish difficult on an unicycle! 
 

Offline ukmicky

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Ice skating, speed and falling over.
« Reply #4 on: 26/08/2007 14:40:55 »
Quote
As we are adapted to walking upright we have a built in system for keeping our centre of gravity directly above our feet or the point of contact of our bicycle tires or ice skates with the ground (or ice) as the case may be.
when we ride a bicycle we have to move this point of contact from side to side by moving the handlebars which is easy when we are moving forward at a reasonable pace but the slower we go the more sluggish the responce becomes until when we are stationary then we can do nothing.
I would have though a bicycle is different as it has spinning wheels which act like Gyroscopes and therefore once the wheels are turning they hold the bike up resisting any change to direction or axis.
 

Offline syhprum

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Ice skating, speed and falling over.
« Reply #5 on: 26/08/2007 17:42:18 »
experiments have shown that the gyroscopic effect is very small the main effect is the feedback to the bodies auto balancing system.
 

Offline ukmicky

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Ice skating, speed and falling over.
« Reply #6 on: 26/08/2007 18:48:00 »
Its a mixture of the two as riding a bike with no hands shows or the fact that if a motorcyclist is dismounted the bike can continue upright until its speed reduces to the point where the gyroscopic effect is no longer strong enough to keep the bike moving in a sraight line. But of course a motorbike on average moves faster than a bicycle
« Last Edit: 26/08/2007 18:53:20 by ukmicky »
 

Offline syhprum

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Ice skating, speed and falling over.
« Reply #7 on: 26/08/2007 19:06:40 »
Motorcycle wheels are of course much larger and heavier than bicycle wheels hence the gyroscopic effect is much greater.
When riding 'no hands' directional instruction is fed back to the machine by pressure on the saddle with the thighs
 

Offline ukmicky

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Ice skating, speed and falling over.
« Reply #8 on: 26/08/2007 20:56:55 »
Its speed dependent, go fast enough on a bicycle with no hands about 10 to 15mph depending on the bike and the bike will remain up right with out any aid of the rider apart from peddaling , so much so that to turn a corner with no hands requires you to lean into the bend ,whist at the same time the bike is trying to lift back up..
« Last Edit: 26/08/2007 21:06:47 by ukmicky »
 

Offline syhprum

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Ice skating, speed and falling over.
« Reply #9 on: 26/08/2007 21:09:36 »
Try replacing the rider with an inanimate dummy and see how long it stays upright!.
Its all about the riders automatic balacing reaction.
 

lyner

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Ice skating, speed and falling over.
« Reply #10 on: 26/08/2007 23:38:28 »
I thought that the thing that does most to keep a bicycle upright is the geometry of the front forks and the offset between the axis of the top bracket (steering  bit) and the  spindle of the front wheel. When you start to fall one way, the system automatically steers you towards that direction and produces a force (or, more strictly, moment) to bring you upright again - but, possibly going in a slighty different direction.  A mere detail,.
I know it's possible to make a bike that is virtually unridable by messing with the front fork geometry.
The faster you are going, the stronger the self-righting effect.
 

Offline ukmicky

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Ice skating, speed and falling over.
« Reply #11 on: 27/08/2007 00:23:58 »
 

lyner

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Ice skating, speed and falling over.
« Reply #12 on: 27/08/2007 23:48:12 »
Somehow that doesn't surprise me. Old chestnut no. 342, probably.
 

paul.fr

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Ice skating, speed and falling over.
« Reply #13 on: 28/08/2007 03:19:52 »
Somehow that doesn't surprise me. Old chestnut no. 342, probably.

342, eh. I wonder how many are left?
 

Offline syhprum

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Ice skating, speed and falling over.
« Reply #14 on: 28/08/2007 08:03:22 »
Let us get back to the original question about ice skating to which I feel I gave an adequate answer.
I was foolish to mention bicycles as this gyroscopic red herring always comes up, I wanted to make the point that a long base makes the the backwards  and forwards correction easier so I compared a bicycle to an unicycle I should of compared skates to skis!
 

lyner

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Ice skating, speed and falling over.
« Reply #15 on: 28/08/2007 10:04:46 »
A few relevant ideas -  this isn't a structured argument but I think the sense is in there, somewhere:

There is one big difference between the way we keep upright on bikes and skates etc. and the way we keep upright when walking. When we walk, we have  both  'side to side' and 'fore and aft' control; friction and a width of base can be used to provide a couple around two (three?) axes. This is used to avoid falling backwards, forwards or sideways. 

When skating/ cycling or skateboarding,  one , (or both) of these is missing. Beginners stand with their blades side by side and parallel - they end up on their backside; there is no restoring couple.  Crossing your skates brings you back into the ordinary ' standing up' condition.
Once you are moving, the situation is more complex.
We  get our 'righting moment' largely from the dynamics of the situation but I feel more stable whilst accelerating at speed because I am pushing back with  a blade, held at an angle 'across' the direction of motion. (That's essential, if you want to push against the ground behind.)
 To change direction, rather than 'twisting your ankle' (syphrum) what you often do is to LEAN and PUSH with the outside blade. Also, you do not need, actively, to move the handlebars on a bike, to change direction. You just LEAN. I'm not an expert but I can cycle for miles with no hands, turning corners and pedaling.
On skates, you do, actually, have a square base - you can choose to put your feet side to side or forward / backwards but, once you a traveling at speed,  you can't get your legs far enough apart to keep stable - you need a combination of leaning and  moving on a curved path (as with a racing motor bike).
As for the Physics of it - the faster you go, whether skating or cycling, the greater the centripetal (centrifugal) force
for a given radius of motion:
force = m v^2 / r   (motion in a circle - A level  - first year)
and, because of the squared factor for v, if you double your speed, you get the same restoring force (moment) for a radius of four times. Velocity talks.
 

Offline syhprum

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Ice skating, speed and falling over.
« Reply #16 on: 28/08/2007 10:33:26 »
Leaning on a bicycle means of course pushing the machine from side to side when the geometry of the suspension (when you are moving forward) results in turning the direction the front wheel points until the point of suspension on the ground is adjusted to be beneath your C of G by your balancing reflex.
This is why a bicycle with perverse suspension geometry is very difficult to ride.
When you are travelling on a curved path the idea of what is 'beneath' must be modified by the centripetal force
« Last Edit: 28/08/2007 11:21:15 by syhprum »
 

paul.fr

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Ice skating, speed and falling over.
« Reply #17 on: 04/09/2007 16:20:46 »
The discussion has now moved on to the physics of tightrope walking. Therefore the topic has been split in to two discussions.

The new topic " The Physics of Tightrope walking"
can be found here http://www.thenakedscientists.com/forum/index.php?topic=9902.msg119673#msg119673
 

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Ice skating, speed and falling over.
« Reply #17 on: 04/09/2007 16:20:46 »

 

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