Crash strategy?
#101
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#102
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Sir Bedevere:
...and that, my liege, is how we know the Earth to be banana shaped.
King Arthur:
This new learning amazes me, Sir Bedevere. Explain again how sheep's bladders may be employed to prevent earthquakes.
...and that, my liege, is how we know the Earth to be banana shaped.
King Arthur:
This new learning amazes me, Sir Bedevere. Explain again how sheep's bladders may be employed to prevent earthquakes.
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#103
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I didn't notice that this was a continuation of your question, even if phrased belligerently, so I'll answer.
You absolutely need to find or estimate the time it takes to come to a stop, because the force you feel is the momentum change divided by the time it takes. Literally all of your horizontal momentum is accounted for in this phase (remember your vectors). Once you have done that, then you've accounted for all of the momentum changes and you'll know that vertical momentum is changed in a short time during the initial impact, and horizontal momentum is changed in the period where you are slowing along the ground. Exclusively in that phase.
You absolutely need to find or estimate the time it takes to come to a stop, because the force you feel is the momentum change divided by the time it takes. Literally all of your horizontal momentum is accounted for in this phase (remember your vectors). Once you have done that, then you've accounted for all of the momentum changes and you'll know that vertical momentum is changed in a short time during the initial impact, and horizontal momentum is changed in the period where you are slowing along the ground. Exclusively in that phase.
Here's your answer. Let's assume a 50kg rider traveling at 9 m/sec (32 kph or 20 mph). If we assume that the time to stop takes 0.1 second, the impact is 4500N. If we extend the time to 0.2 seconds...which is a very long time for sliding at 20 mph...the force of the impact is 2250N. For the metrically challenged, that 1100 pounds of force and 500 lb of force. Neither is going to leave the rider in great shape.
Regarding your answer to noglider, I'm afraid you got that wrong as well. You will find yourself sliding at 200 mph across the ice. If you believe that part of that impact is from the 200 mph, then where do you think that momentum went??? You're still the same mass, still the same velocity, therefore still have the same momentum.
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#104
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Here's your answer. Let's assume a 50kg rider traveling at 9 m/sec (32 kph or 20 mph). If we assume that the time to stop takes 0.1 second, the impact is 4500N. If we extend the time to 0.2 seconds...which is a very long time for sliding at 20 mph...the force of the impact is 2250N. For the metrically challenged, that 1100 pounds of force and 500 lb of force. Neither is going to leave the rider in great shape.
That's not even close, sliding or rolling, and at least an order of magnitude off for rolling.
At 200 mph ice isn't going to frictionless. Nor would it be all that smooth. A human body dropped from 2 feet at 200 mph is going to go through significant deceleration, probably lots of tumbling and end up broken and battered. Same thing happens at 100 mph. Look at the injuries that can result from a relatively short drop from a bicycle at only about 20 mph.
You're getting there, realizing that the "200 mph" part is entirely separate from the "2 ft fall" part. ALL of the horizontal momentum is taken up by friction and by whatever rises from the pavement. NONE of the horizontal momentum is exchanged from the impact.
Now, to test your idea of "significant deceleration" and the tossing about, how much of your speed is reduced in say, 1 second, sliding on the flat, nearly frictionless, wet ice? Almost none? That means your change in momentum is also "almost none", which means you wont have those violent forces throwing you about.
#105
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In a box-in accident, I'm putting my efforts into changing the direction of the bike to try to make the blow as glancing as possible and also hoping for a space to open up at the margin. The last time this happened to me, I was screaming so loud that I was able to get the driver to change course at the last possible millisecond, and the collision never occurred. At the speed I was going and the nearness to the vehicle, jumping off the bike would have been suicidal. And this occurred when a driver cut across four lanes of traffic at a high speed to illegally swerve into the breakdown lane directly in front of me, so please don't try to pin this one on me.
A much earlier incident I changed course so hard succeeded in pretzeling a Cinelli 1/A stem. Basically screwed bike into ground. Some other damage to bike. Again no injury to me. No way I could decipher if a rear exit off the bike would have worked better on that occasion.
Rear exit is not something most would even think of. Surprisingly easy once tried.
Oh, I found store stock for that large helmet. It fits. First one that fits in ten years. I have looked before. So thank you again.
#106
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Going over is easiest. Works quite well. Done it, three occasions. Does not injure riders in the pile either. What is required is a lesson. Once you see someone else do it seems very simple. And is.
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#107
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I'm laughing at myself, embarrassed.
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#110
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OK, back on topic, as I said earlier, rehearsal is a very useful tool. It doesn't have to be a close-to-realistic simulation. I was amazed at how well it worked, because I didn't develop the technique for that reason.
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#112
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High speed bike crashes on ice. Lots of them. There are other vids from other cameras, this one is good enough.
Mostly they get up and keep riding.
Mostly they get up and keep riding.
#114
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High speed bike crashes on ice. Lots of them. There are other vids from other cameras, this one is good enough.
https://www.youtube.com/watch?v=m2gwFkCU1Q4
Mostly they get up and keep riding.
https://www.youtube.com/watch?v=m2gwFkCU1Q4
Mostly they get up and keep riding.
----------------------------
I've fallen off my motorcycles at speeds ranging from 0 to 70 mph with dirt bikes and street bikes. 0 mph were comical fall overs. All others were above 25 mph. My physical well being depended on if a part of my body gained traction on touching the ground causing me to tumble, or if I landed into something soft or hard.
Personally, I got lucky and only lost skin, got heavily bruised, and one bell ringer of a concussion* with a helmet on. Friends of mine suffered broken bones, head injury, one collapsed lung, loss of skin from road rash or burns, etc.
*one out of 5 concussions that I know of.
Last edited by FiftySix; 11-19-19 at 07:04 PM.
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Bravo, OP!
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I suspect a lot of the argument comes from differences in speed and other riding habits as well as knowledge of our own reaction times. We can probably trade anecdotes for years and never get to any kind of conclusion.
Really happy the helmet fits you. We lucked out that they had one in stock at an lbs in Amherst, MA. My son was about as surprised as you that we found one that fit.
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Before it's a completely dead thread, does anyone still disagree with this?
"the added speed is parallel to the ground, and doesn't add anything to the vertical impact of the fall, right? The impact you feel from the speed is added by deceleration from friction, and whatever rises from the surface, including "concave up" shaped road grade. On a flat and smooth road, you could fall at 100 mph and that fall is not the danger. Getting part of your body wrenched back, or sliding into something, is where the danger is."
"the added speed is parallel to the ground, and doesn't add anything to the vertical impact of the fall, right? The impact you feel from the speed is added by deceleration from friction, and whatever rises from the surface, including "concave up" shaped road grade. On a flat and smooth road, you could fall at 100 mph and that fall is not the danger. Getting part of your body wrenched back, or sliding into something, is where the danger is."
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Before it's a completely dead thread, does anyone still disagree with this?
"the added speed is parallel to the ground, and doesn't add anything to the vertical impact of the fall, right? The impact you feel from the speed is added by deceleration from friction, and whatever rises from the surface, including "concave up" shaped road grade. On a flat and smooth road, you could fall at 100 mph and that fall is not the danger. Getting part of your body wrenched back, or sliding into something, is where the danger is."
"the added speed is parallel to the ground, and doesn't add anything to the vertical impact of the fall, right? The impact you feel from the speed is added by deceleration from friction, and whatever rises from the surface, including "concave up" shaped road grade. On a flat and smooth road, you could fall at 100 mph and that fall is not the danger. Getting part of your body wrenched back, or sliding into something, is where the danger is."
#121
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Before it's a completely dead thread, does anyone still disagree with this?
"the added speed is parallel to the ground, and doesn't add anything to the vertical impact of the fall, right? The impact you feel from the speed is added by deceleration from friction, and whatever rises from the surface, including "concave up" shaped road grade. On a flat and smooth road, you could fall at 100 mph and that fall is not the danger. Getting part of your body wrenched back, or sliding into something, is where the danger is."
"the added speed is parallel to the ground, and doesn't add anything to the vertical impact of the fall, right? The impact you feel from the speed is added by deceleration from friction, and whatever rises from the surface, including "concave up" shaped road grade. On a flat and smooth road, you could fall at 100 mph and that fall is not the danger. Getting part of your body wrenched back, or sliding into something, is where the danger is."
#122
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Before it's a completely dead thread, does anyone still disagree with this?
"the added speed is parallel to the ground, and doesn't add anything to the vertical impact of the fall, right? The impact you feel from the speed is added by deceleration from friction, and whatever rises from the surface, including "concave up" shaped road grade. On a flat and smooth road, you could fall at 100 mph and that fall is not the danger. Getting part of your body wrenched back, or sliding into something, is where the danger is."
"the added speed is parallel to the ground, and doesn't add anything to the vertical impact of the fall, right? The impact you feel from the speed is added by deceleration from friction, and whatever rises from the surface, including "concave up" shaped road grade. On a flat and smooth road, you could fall at 100 mph and that fall is not the danger. Getting part of your body wrenched back, or sliding into something, is where the danger is."
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Even if it hit you (gasp) you'd still only suffer injury in relation to the difference in momentum imparted.
If it barely made contact (shallow velocity vector) it wouldn't impart that much energy & would do so over a large moment. You'd end up with a cut or less depending on how shallow it made contact and the path of the bullet little affected & nothing more.
If it made a direct hit (perpendicular vector) all of the energy would be imparted in a very short moment over a very tiny area. You'd have a tiny enterance hole & catastrophic amount of damage caused by absorbing a huge amount of energy in a very small amount of time.
This whole thread has circled the drain endlessly regarding rate of decelleration (or more directly rate of energy change) being the cause of injury. It's why cars have crumple zones & bullet proof vests do their thing. The force is distributed over a larger area for a longer time to reduce the force to a rate that can safely be imparted by the occupant.
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#125
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No, as described above there are two components to the forces you'll feel. One, the momentum due to the fall. Two, the momentum due to the velocity. The bullet's momentum will result in piercing your skin and possibly other organs.
In falling, you have the same two components. Momentum due to falling is the same. But the effect of the linear velocity (ie, change in momentum) is distributed over time. The greater the time interval, the less force you feel. That's the main point of rolling, the other point being avoiding abrasion and localized forces on your skeleton and soft tissue. And the reason why sliding is better than hitting the ground and never moving. The longer it takes to stop, the less force there is.
If you meant that as a counter-example, do you see why it fails?