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Post by owenbrau on Oct 8, 2009 6:27:10 GMT -5
You're still talking about hitting at the same speed. That's not what happens. If you are sitting still, your only velocity is that from falling. If you fall while moving forward, you have not only the velocity you were moving at, but that velocity from falling.
There is a classic thought experiment. You have a cannon at the top of a tower. You fire the cannon horizontally, and at the same time drop a cannonball. They both hit the ground at the same time. That's because they one you fired has horizontal velocity, but it's vertical velocity comes only from gravity, same as the one you dropped. It is going a lot faster when it hits, but the downward vector is identical.
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Post by JR on Oct 9, 2009 6:15:21 GMT -5
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Post by Alsenor on Oct 9, 2009 20:53:15 GMT -5
Yes, owen, you're right. But you should still try the experiment I suggested before. Forget the physics, use common sense: Direst blow vs glancing blow!
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Post by owenbrau on Oct 9, 2009 22:33:23 GMT -5
A low velocity, direct blow, vs. a higher velocity glancing blow, where the vertical component of the glancing blow is equal to the total of the direct blow, the impact, g-forces sustained by the two, etc. will be essentially the same. If anything, the higher velocity but glancing impact will do more damage not less, due to drag imparting spin, and abrasion. Your experiment is hitting at the same total velocity, not the same vector velocity.
Falling from 5 feet results in a velocity of about 18 ft/sec. That's about 12 mph. If you go down while riding at 40 mph, you hit the ground going about 40 mph horizontally, and 12 mph down. That isn't 52 mph, btw; it's about 42 mph, diagonally towards the ground at impact.
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Post by Alsenor on Oct 9, 2009 23:18:55 GMT -5
...and if you hit the concrete square at 12 mph you have a better chance of cracking your skull than if you hit it at any speed with a glancing impact. Try it! Practice trumps theory.
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Post by owenbrau on Oct 10, 2009 8:33:48 GMT -5
...and if you hit the concrete square at 12 mph you have a better chance of cracking your skull than if you hit it at any speed with a glancing impact. Try it! Practice trumps theory. Quite simply, you are wrong.
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Post by Alsenor on Oct 10, 2009 10:51:48 GMT -5
...and if you hit the concrete square at 12 mph you have a better chance of cracking your skull than if you hit it at any speed with a glancing impact. Try it! Practice trumps theory. Quite simply, you are wrong. Seems you already have tried the experiment! ;D Have a good one.
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Post by owenbrau on Oct 10, 2009 13:13:23 GMT -5
If you are moving towards the wall at 12 mph, it doesn't matter if you are also moving parallel to the wall at any velocity or none, you still hit it at 12 mph. On a scooter, moving forward does not slow down your fall (see the cannonball example above).
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Post by Alsenor on Oct 10, 2009 16:12:01 GMT -5
If you are moving towards the wall at 12 mph, it doesn't matter if you are also moving parallel to the wall at any velocity or none, you still hit it at 12 mph. On a scooter, moving forward does not slow down your fall (see the cannonball example above). OK, my last try! You actually gave yourself the best argument: "moving forward does not slow down your fall"! Which should make you realize that it is the "slowing down" that causes most damage. When you run into the proverbial brick wall you ARE slowed down instantly, and your brain may try to come out through your eyes. That is why a glancing impact is so much less traumatic, since it does NOT bring your skull to a sudden stop.
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Post by owenbrau on Oct 10, 2009 19:19:59 GMT -5
You are not making sense. No matter how fast you are moving forward, you stop moving down at exactly the same rate. A glancing blow is only less traumatic if you are moving at the same velocity in both cases; 12 mph straight at the ground or 12 mph at some angle to the ground. That isn't what happens. If you fall at speed, you still fall down at the same speed, and it doesn't matter that it's glancing because your head still has to stop from that velocity even as it continues to move forward. Learn about vectors. www.ac.wwu.edu/~vawter/PhysicsNet/Topics/Vectors/ProjectilesMotion.html
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Post by Alsenor on Oct 10, 2009 22:46:11 GMT -5
Sorry, when I say "last try" I mean it. None of those physics formulas mean beans in the face of good judgment and experience.
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Post by owenbrau on Oct 11, 2009 7:02:40 GMT -5
And I seriously doubt your experience actually shows what you claim. And judgment has nothing to do with physics. You are wrong, the fact that you are riding forward does not diminish the impact of falling down. If that were true, it would be possible to travel so fast that when you hit there is no impact whatsoever. Quite simply, you don't know what you're talking about. You're also probably very bad at pool.
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Post by Alsenor on Oct 11, 2009 12:07:58 GMT -5
Cute, you sound just a bit less respectful than my son, who is about your age. FYI, I actually happen to be a 3-C billiard player and teacher, with a number of trophies, and many grateful students. Most of our new students are advanced ex-pool or snooker players, who would like to learn a more challenging game. The more talented ones usually take at least a couple of years to compete at the lower levels in 3-C billiards.
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Post by JR on Oct 11, 2009 19:55:20 GMT -5
Al I tell ya just give it up, cause we all know these youth of today can't be told anything!! You don't have to convince me at 70 years of age you've learned a thing or two! Used to hang around the old pool halls myself when I was younger but like a lot of things now they've been replaced with the smart couch potatoes playing Wii now a days! Loved to play that snooker and 9-ball!! Ahhhh those were the days! Heck I can gather up a lot of these couch potatoes and not even do they not even know what a pool ball is they couldn't even change a flat tire!! LOL en.wikipedia.org/wiki/EinsteinFunny thing about this dude, he was pretty good with physics too and you and I were here when he figured it all out! They didn't have Wii's then either!! LOL JRr
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Post by Alsenor on Oct 12, 2009 0:21:24 GMT -5
You are right, it's just a waste of time. The types who get pushed through fancy colleges nowadays and then come out getting hired by corporations to write the kind of manuals not worth the paper they are printed on. Smart Alecs is the term that comes to mind. Some grow out of it over the years, but some just turn into old smart alecs. I too, used to think I know it all when I was in my forties.
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Post by owenbrau on Oct 12, 2009 6:26:24 GMT -5
It is a waste of time. And you're wrong. Sliding doesn't diminish the impact of hitting the ground.
Let's try pool, then.
If you hit a ball a glancing shot, very little of the total energy is transferred to the new ball, right? I get that. But if you hit it straight on, you can't use that much force, because you fling the ball across the room, so you just tap it. Falling down while sitting still, that's the tap. Now if you hit the tap in a glancing shot, nothing happens, very little is transferred. The full-force glancing shot, that's falling down while moving at speed. The tap is still there. And it moves the target ball the same as the light tap straight on. And that target doesn't know or care which shot hit it, it moves the same way.
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Post by JR on Oct 12, 2009 6:30:57 GMT -5
Well who do ya think common folks are going to beleive a fellow whao has been around for 70 years or someone like you who spends his time in a tatoo parlor getting all dolled up? BTW can you change a flat tire?
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Post by Alsenor on Oct 12, 2009 10:53:13 GMT -5
Well who do ya think common folks are going to beleive a fellow whao has been around for 70 years or... Well, therein lies the difference between the young man and myself. I am not trying to make anyone believe me, or to force my "knowledge" onto others - everyone can judge for himself. While he keeps telling me that I "am wrong". The objective of any civil discussion is not to convince the other party of one's own convictions, but to put forth logical arguments, with an open mind and respect for opposing opinions. Owen does not show that. He keeps telling us about a very basic physical law (which we all learned way before he was born), that has very little to do with the problem at hand. Here it is once more: The crucial damage in high speed crashes is not necessarily caused by the initial contact, but by the deceleration of your body when it hits the (more or less) "immovable object". To translate this into a practical scenario, your helmet (with your head in it!) hits the road at a high forward velocity, admittedly at the same vertical speed as if you were falling from a chair. But here comes the clincher: you scrape your helmet, keep flying forward until you hit the tree, bridge pillar, or whatever is in the way of your path, which breaks you into pulp. Your brain is not trying to come out your eye sockets until your head is coming to that sudden stop. The billiard ball is doing the same thing: a feather hit on an object ball does not slow down the cue ball substantially, but a full hit robs it of most or all of its speed, depending on its own top spin or draw.
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Post by owenbrau on Oct 12, 2009 13:39:50 GMT -5
Here's the clincher; when you scrape, you still stop falling down. You're still going forward, but not down anymore, so there is a deceleration in that direction. The energy imparted by gravity does not change direction. The forward motion doesn't matter, the downward impact is still the same. Which brings us back to my original point; helmets are important even if you don't ride fast.
I'm not trying to force anything on you, anymore than a teacher is "forcing" facts on a student.
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Post by owenbrau on Oct 12, 2009 13:52:48 GMT -5
JR, you truly are amazing. Alesnor is remaining civil, why can't you?
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Post by JR on Oct 12, 2009 16:21:38 GMT -5
JR, you truly are amazing. Alesnor is remaining civil, why can't you? Thank ya there Owenbrau I do even amaze myself sometimes! LOL Wasn't trying to be uncivil ! In fact just trying to let Alesnor know that it is futile to even try to make you understand, trying to argue his point and just let it be! Now how more civil can ya be than that? LOL BTW really I'm serious can you change a flat tire maybe even a scooter tire?
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Post by CCProf on Oct 12, 2009 16:35:18 GMT -5
Let's skip the Physics guys. If you go down at any speed, it's going to hurt!
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Post by Alsenor on Oct 12, 2009 16:40:52 GMT -5
Owen, you seem to have forgotten that my original comment to your post actually supported your argument "that falling from a 50cc scooter you hit the ground just as hard" as from one with higher speed: You falling down fall just as far. hit just as hard. Actually, at slower speeds you fall at a more acute angle to the ground and are more likely to crack your skull than at higher speeds, which gives you a flatter approach angle to the ground and makes you slide more. Roadburn is not so much fun either of course... The point I was trying to make is that in high speed crashes the real damage is done by your body coming to a forceful stop, while your innards are still flying forward. When you fall from a second floor window it is the ground that stops your body, but when you lose it on your bike at 50mph or more it will be the first tree or post or wall, etc.. And that will be what breaks your body.
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Post by teknoyd on Oct 12, 2009 21:10:39 GMT -5
When I was a teenager one of the guys I knew was racing his Norton Commando against one of the other guys on his 3 cylinder Kawasaki late at night, or early in the morning depending on your perspective.
Being drunk and stupid is a bad combination anytime, but it is an especially bad combination on a bike at an extremely high rate of speed.
After he won the race, he let go of the handlebars and put his hands up in the air in a sort of "victory cheer." The hundred mile an hour-plus wind blew him over backwards, and he slid and slid and slid some more.
Fortunately, he was on a straight stretch of highway and while he was sliding, he didn't hit anything like a sign, lightpole, fence post, curb, etc.. If he had, the abrupt "deceleration trauma" probably would have been the end of him.
He didn't break anything, but the rest of that summer he only wore big baggy shorts and really loose t-shirts while he grew new skin. Ouchie.
- Tek
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Post by Alsenor on Oct 12, 2009 21:30:30 GMT -5
Very good case in point, Tek. You could break a limb easier by falling from a horse.
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Post by harrywr2 on Oct 13, 2009 12:42:35 GMT -5
Being drunk and stupid is a bad combination anytime, but it is an especially bad combination on a bike at an extremely high rate of speed. - Tek That's the definition of a squid. Alcohol and excessive speed are way bigger factors of whether one will become an unfortunate statistic rather then whether you wear 'all the gear all the time'. I was riding the other day and a crotch rocket passed me in a blind hairpin turn. He was wearing 'all the gear'. I guess he figured that his gear would protect him if a car had been coming in the opposite direction.
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Post by JR on Oct 13, 2009 14:36:21 GMT -5
Being drunk and stupid is a bad combination anytime, but it is an especially bad combination on a bike at an extremely high rate of speed. - Tek That's the definition of a squid. Alcohol and excessive speed are way bigger factors of whether one will become an unfortunate statistic rather then whether you wear 'all the gear all the time'. I was riding the other day and a crotch rocket passed me in a blind hairpin turn. He was wearing 'all the gear'. I guess he figured that his gear would protect him if a car had been coming in the opposite direction. Well if he had got ran over at least he would have looked good!! LOL JRR
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Post by owenbrau on Oct 13, 2009 15:19:41 GMT -5
Being drunk and stupid is a bad combination anytime, but it is an especially bad combination on a bike at an extremely high rate of speed. - Tek That's the definition of a squid. Alcohol and excessive speed are way bigger factors of whether one will become an unfortunate statistic rather then whether you wear 'all the gear all the time'. I was riding the other day and a crotch rocket passed me in a blind hairpin turn. He was wearing 'all the gear'. I guess he figured that his gear would protect him if a car had been coming in the opposite direction. On the other hand, if he were riding well within reason and figured he didn't need to wear all that stuff because he didn't ride that way, then a car coming the other way blew the turn and took him out, he'd probably wish he'd been wearing the gear. And this particular accident occurred to a scooter rider during a rally, the rider (who was in fact wearing the gear) works for Scoot! magazine, and survived because he had on the gear. Thinking your gear makes you perfectly safe (a position not one person on this board has taken in any of the iterations of this argument) is stupid. Thinking that you are too good, too experienced to need to wear it, is too.
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Post by JR on Oct 13, 2009 16:58:17 GMT -5
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Post by Alsenor on Oct 13, 2009 21:23:05 GMT -5
Hell of a meat head! ;D
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