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Roller Disaster Averted

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Roller Disaster Averted

Old 12-07-06, 08:43 PM
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Roller Disaster Averted

A good lesson was learned tonight. Just as I was clipping in and getting ready for a spin on the rollers the dog came by and dropped a squishy rubber ball in the framework of the rollers. As I spun the pedal forward the ball rolled under the front roller and wedged between the floor and the roller. It was wedged so tight that I had to get off and get weight off of the rollers to dislodge it.

I hate to think what would have happened at speed. I ride about 8 feet in front of an entertainment center and would have shot into it like a missile. Needless to say that "hide doggie toys" is on my pre-roller checklist.

I am now wondering if the dog is trying to get rid of me.
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Old 12-07-06, 08:49 PM
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I'm not a physics expert, but I don't know that you would've ruined your equipment. You only have forward momentum if your wheels are magically able to hit the ground while still in motion...

Anywho, I understand your sentiments. My cat always looks very curiously at the wheels spinning round and round. I was fearing that he may stick his paw in the wheel and thus cause pain for me, death or dismemberment for himself, and a lot of scheiße for me to clean up. Now I close the door on him.
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Old 12-07-06, 09:00 PM
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Hard telling what might have happened but it is nice having the dog around because he keeps the cats away. Cats are way too curious. The dog eventually falls asleep next to me while I'm riding
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Old 12-07-06, 09:06 PM
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i was riding on my rollers and my wheel slid off the side at pretty high speed. My tire touched the metal rail and stopped immediately, filling my room with the stench of burnt rubber. I was personally suprised that I didnt go flying when that happened.
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Old 12-07-06, 09:30 PM
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There's a rule in my house: no free-roaming animals while I'm on the rollers. ever.
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Old 12-07-06, 11:36 PM
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Originally Posted by bdcheung
There's a rule in my house: no free-roaming animals while I'm on the rollers. ever.
Good rule. I don't even allow them when I am on the trainer.
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Old 12-08-06, 12:01 AM
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Originally Posted by G5Ti
I'm not a physics expert, but I don't know that you would've ruined your equipment. You only have forward momentum if your wheels are magically able to hit the ground while still in motion...
Easily done on rollers, my friend. Easily done. That being said, I don't think I've ever launched myself any more than 3 or 4 feet in front of my rollers before. I imagine it's possible to get further, though.
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Old 12-08-06, 01:43 AM
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Yeah, the wheels stop when they hit the ground. They don't have enough momentum to launch you forward.
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Old 12-08-06, 06:10 AM
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I learned this week how to ride straight off of my rollers without falling. This has no practical use, but it is kind of cool. I think the ball would have been some pretty bad news for you.
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Old 12-08-06, 06:37 AM
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next time give him a shot of chili-spray
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Old 12-08-06, 08:12 AM
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Your dog was simply telling you that you needed more resistance. You can't a better personal trainer for the money.
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Old 12-08-06, 08:27 AM
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no free roaming young kids or animals near rollers.
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Old 12-08-06, 08:32 AM
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Your front wheel likely would have stopped because there was no pedal force driving it. As for the rear wheel, well, let's just say the header into the TV hurts about as much as you'd think.
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Old 12-08-06, 08:34 AM
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obviously not a good situation, but the real risk is that you would have come off and fallen sideways.

Riding on the road at 25mph, you have the momentum of say 200lbs (your weight, and the bike's weight), plus the tiny bit of momentum from 3 pounds of wheels and tire spinning.

Riding on the rollers at 25mph, you got the inertia of your and the bikes 200lbs sitting still, and the momentum of 3lbs of wheels and tires spinning. If you come off the 3lbs of wheels spinning can't accelerate the 200lbs sitting still to any significant extent.

Both physics, and the shared experience of many who have done it tell you, that you do not shoot forward when you come off the rollers.
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Old 12-08-06, 10:54 AM
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Originally Posted by nobrainer440
Yeah, the wheels stop when they hit the ground. They don't have enough momentum to launch you forward.
I have been launched forward many times (I suck at rollers and have given up long ago, though), but I have never been launched more than a few feet because the only momentum launching me forward is the wheels. 1500-2000 grams of mass spinning at around 200-300 rpm does in fact have momentum though!
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Old 12-08-06, 11:05 AM
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Yeah, it doesn't send you through the house like the movies would have us believe, but a couple feet is enough if you haven't planned for that rapid dismount.
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Old 12-08-06, 11:09 AM
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Just a correction on all this momentum talk:

The momentum while sitting on the rollers not pedalling is zero.
The momentum while sitting on the rollers pedalling is zero.
The momentum while sitting on the rollers pedalling the instant the tires hit the floor is zero.

Momentum is mass times velocity. The velocity in the x direction is zero so momentum is zero. It is only after you start going forward that there is any momentum.

The answer lies in friction. If the tires spin and you smell burnt rubber, the tire spinning is overcoming the friction, so the tire spins. If the tire spinning does not overcome the friction, it has grip and will propel you forward... Slowly.

If I'm not applying the physics concepts correctly, I hope will someone corrects me.
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Old 12-08-06, 11:25 AM
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Originally Posted by TryingMyBest
Just a correction on all this momentum talk:

The momentum while sitting on the rollers not pedalling is zero.
The momentum while sitting on the rollers pedalling is zero.
The momentum while sitting on the rollers pedalling the instant the tires hit the floor is zero.

Momentum is mass times velocity. The velocity in the x direction is zero so momentum is zero. It is only after you start going forward that there is any momentum.

The answer lies in friction. If the tires spin and you smell burnt rubber, the tire spinning is overcoming the friction, so the tire spins. If the tire spinning does not overcome the friction, it has grip and will propel you forward... Slowly.

If I'm not applying the physics concepts correctly, I hope will someone corrects me.
the wheels have momentum, but it's not enough to move the bike very far or very fast when it hits the carpet.
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Old 12-08-06, 11:51 AM
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Originally Posted by merlinextraligh
the wheels have momentum, but it's not enough to move the bike very far or very fast when it hits the carpet.
For a wheel to move a bike in a direction due to momentum, it must have a velocity in that same direction. What is the wheel's velocity in the direction the bike will move?

Velocity is meters per second. How many meters is the wheel moving per second? I think the answer is zero. The wheel isn't moving in the x-direction at all.

The wheel may have angular momentum, but it's velocity in the x-direction is zero.
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Old 12-08-06, 11:55 AM
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Originally Posted by hoogy
I ride about 8 feet in front of an entertainment center and would have shot into it like a missile.
As mean as this sounds, can you please set up a videocamera and tripod next time your dog is playing in the area with toys.....that would be a great video for YouTube.
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Old 12-08-06, 12:31 PM
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Originally Posted by TryingMyBest
For a wheel to move a bike in a direction due to momentum, it must have a velocity in that same direction. What is the wheel's velocity in the direction the bike will move?

Velocity is meters per second. How many meters is the wheel moving per second? I think the answer is zero. The wheel isn't moving in the x-direction at all.

The wheel may have angular momentum, but it's velocity in the x-direction is zero.
Ok the wheel is rolling in one direction. Given conservation of momentum, it wants to continue rolling in that direction. When it hits the carpet, given friction between the carpet and the tire, the rolling wheel will push the bike forward. However the momentum of the wheel is so nominal in comparison to the inertia of the bike and the rider it doesn't push it very far.


So the wheel isn't moving in the X direction at all, but when you put the spinning wheel on the ground, its going to roll foward.

If you don't believe me, take a bike tire, hold it by the quick release levers, spin it, and then set it on the ground. I bet it rolls away from you.
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Old 12-08-06, 12:41 PM
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In all the discussion of the physics of a moving bicycle wheel contacting the carpet, I propose another consideration. The forward movement (and hence momentum) of a bicycle is the result of pedaling. If you're pedaling at 100 RPM on rollers and suddenly become detached from said rollers, unless you stop pedaling by the time the wheel hits the carpet, there is a transfer of power and some forward movement will result.
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Old 12-08-06, 01:05 PM
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Originally Posted by trin2du
In all the discussion of the physics of a moving bicycle wheel contacting the carpet, I propose another consideration. The forward movement (and hence momentum) of a bicycle is the result of pedaling. If you're pedaling at 100 RPM on rollers and suddenly become detached from said rollers, unless you stop pedaling by the time the wheel hits the carpet, there is a transfer of power and some forward movement will result.
Yes...and when I jump as high as I can, I can actually push the earth out of it's normal orbit. Of course it corrects it's orbit as it then pulls my own mass back to itself, also pulling itself back into orbit.
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Old 12-08-06, 01:36 PM
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Originally Posted by GuitarWizard
As mean as this sounds, can you please set up a videocamera and tripod next time your dog is playing in the area with toys.....that would be a great video for YouTube.
I'll get the camera set up tonight and get back to you all tomorrow. ....or not.

After thinking about it more I think that I would have done a slight burnout and fallen over on top of the dog. Not as dramatic as a launch into the TV but it would have gotten my attention.

The bottom line is, squishy ball + rollers + dog = bad
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Old 12-08-06, 06:10 PM
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TryingMyBest is right, the wheel's DIRECTIONAL momentum is still zero since its momentum is simply spinning and not moving. What launches you forward is the friction of the tire when it hits the ground with its spinning momentum. Sorry, my previous statement was poorly worded.

The only correction is that it will not slowly propel you. You will be almost instantaneously propelled, but will also decelerate rapidly because of the lack of momentum, hence the limited range of such adventure.
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