4 ms·

Yes, indeed. Next time you should be very hesitant. Hesitate so much that the out of control car plows into a busy intersection. So many things could go right.

by lrm242 16y ago

Yes, indeed. Next time you should be very hesitant. Hesitate so much that the out of control car plows into a busy intersection. So many things could go right. It could just barely miss that SUV with 4 kids in the back, and I'm sure it would only scare the elderly couple crossing the street. C'mon, seriously? The article is an up-beat account of how things can go right. How under pressure someone made a necessarily quick decision to take action rather than sit on the sidelines and watch as an observer. Do you really think anyone sane-minded individual is going to come away from this article thinking to themselves, "Man, next time I'm on the highway I need to give this a shot"?

zdw 16y ago
If my math is right, the kinentic energy of 2 ton vehicle going 40 MPH is roughly equivalent to 70kg of TNT. That's the kind of fire this guy was playing with, for his life, the life of his family, the life of the other driver and all the bystanders. Not to understate his heroism, but had this gone horribly wrong he'd probably be a Darwin award candidate.
- danparsonson 16y ago
  That's only really a problem if all that energy is transferred to another object (near) instantaneously - for instance if the vehicle hits a stationary object like a car waiting at an intersection. Colliding at a relative speed of only a few miles per hour and then hitting the brakes allowed Innes to dissipate that energy in a more controlled way. Risky, certainly, but I don't think it's as risky as you think it is. edit: as an analogy, think about landing a spaceship on a meteorite - it may be moving fast enough to wipe out civilisation as we know it if it hit Earth, but you could still safely stand on its surface. Relative velocity is key.
  - dmoney 16y ago
    You wouldn't have to use a spaceship. "meteorite" means it's already hit the ground. You could just walk over to it, assuming it didn't wipe out all life.
    - danparsonson 16y ago
      Ah yes, perhaps "asteroid" was the right word? Large piece of rock in space :-)
- cperciva 16y ago
  If my math is right, the kinentic energy of 2 ton vehicle going 40 MPH is roughly equivalent to 70kg of TNT. You're off by a factor of 1000. It's 62.9 grams of TNT: http://www.google.com/search?q=%280.5+*+%2840+mph%29%5E2+*+2+tons%29+%2F+%284.184+*+10%5E9+J+%2F+ton%29 http://www.google.com/search?q=%280.5+*+%2840+mph%29%5E2+*+2...
  - zdw 16y ago
    Ah, my bad. I think the I missed the joule/kilojoule conversion in the reference I was using. Thanks for the correction!
    - hugh3 16y ago
      Not to rub it in, but this is one of those cases where a bit of intuition will get you a lot further than a calculation. Is it plausible that a 2 ton vehicle travelling at 40 mph is equivalent to 70 kg of TNT? Think about the damage done by a crashing minivan. Enough to bend some metal, maybe even knock down a small brick wall. But a 70 kg TNT bomb would easily blow the car into many pieces. Alternatively, how much fuel does it take to accelerate your van from a standstill to 40 mph? A tiny fraction of a litre, which is why you could do it hundreds of times on a tank of gas. Is that tiny fraction of a litre of gasoline going to be energetically equivalent to 70 kg of TNT?
      - cabalamat 16y ago
        > Is it plausible that a 2 ton vehicle travelling at 40 mph is equivalent to 70 kg of TNT? I helps to know that TNT has roughly one tenth the energy density of petrol (4 MJ/kg v. 40 MJ/kg). If it took 7 kg of fuel just to accelerate a vehicle to 40 mph, vehicles would have to carry vastly more fuel than they do.
- Xurinos 16y ago
  I pray I never fear to make the decision to save someone's life, all risks reasonably considered. I have been in a similar situation, and I can tell you: your mettle is tested. You have a tiny amount of time to make a decision, so little that it almost comes down to your instincts. You have enough time to make an assessment of what kind of fallout is about to occur for all parties involved, and your main concern is, hopefully, to minimize the damage. Sure, you may not have all the information at hand to make a perfect decision, and few of us can say to have any reliable precognitive power. You have what you always have in life: some information and the ability to make a choice. Let not fear stay your hand. Fear kills as easily as a heart condition. It can always go horribly wrong, but when something appears by sound reasoning to be inevitable, will you have the courage to intervene?
  - jgrahamc 16y ago
    Very true comment. I did CPR on a guy in the street a few days ago. I'm sure it wasn't perfect, but I'm now told that the guy didn't die. http://blog.jgc.org/2010/10/you-never-think-youll-have-to-do-cpr.html http://blog.jgc.org/2010/10/you-never-think-youll-have-to-do... In the OP the guy used the information he had to make a fast decision. The toughest thing in the situation I encountered was the moment I realized his heart had stopped and needed to decide right then to take action.
- randallsquared 16y ago
  "Not to understate his heroism, but had this gone horribly wrong he'd probably be a Darwin award candidate." It's not heroic if the stakes aren't high.

by lrm242 16y ago

zdw 16y ago

If my math is right, the kinentic energy of 2 ton vehicle going 40 MPH is roughly equivalent to 70kg of TNT. That's the kind of fire this guy was playing with, for his life, the life of his family, the life of the other driver and all the bystanders. Not to understate his heroism, but had this gone horribly wrong he'd probably be a Darwin award candidate.

danparsonson 16y ago
That's only really a problem if all that energy is transferred to another object (near) instantaneously - for instance if the vehicle hits a stationary object like a car waiting at an intersection. Colliding at a relative speed of only a few miles per hour and then hitting the brakes allowed Innes to dissipate that energy in a more controlled way. Risky, certainly, but I don't think it's as risky as you think it is. edit: as an analogy, think about landing a spaceship on a meteorite - it may be moving fast enough to wipe out civilisation as we know it if it hit Earth, but you could still safely stand on its surface. Relative velocity is key.
- dmoney 16y ago
  You wouldn't have to use a spaceship. "meteorite" means it's already hit the ground. You could just walk over to it, assuming it didn't wipe out all life.
  - danparsonson 16y ago
    Ah yes, perhaps "asteroid" was the right word? Large piece of rock in space :-)
cperciva 16y ago
If my math is right, the kinentic energy of 2 ton vehicle going 40 MPH is roughly equivalent to 70kg of TNT. You're off by a factor of 1000. It's 62.9 grams of TNT: http://www.google.com/search?q=%280.5+*+%2840+mph%29%5E2+*+2+tons%29+%2F+%284.184+*+10%5E9+J+%2F+ton%29 http://www.google.com/search?q=%280.5+*+%2840+mph%29%5E2+*+2...
- zdw 16y ago
  Ah, my bad. I think the I missed the joule/kilojoule conversion in the reference I was using. Thanks for the correction!
  - hugh3 16y ago
    Not to rub it in, but this is one of those cases where a bit of intuition will get you a lot further than a calculation. Is it plausible that a 2 ton vehicle travelling at 40 mph is equivalent to 70 kg of TNT? Think about the damage done by a crashing minivan. Enough to bend some metal, maybe even knock down a small brick wall. But a 70 kg TNT bomb would easily blow the car into many pieces. Alternatively, how much fuel does it take to accelerate your van from a standstill to 40 mph? A tiny fraction of a litre, which is why you could do it hundreds of times on a tank of gas. Is that tiny fraction of a litre of gasoline going to be energetically equivalent to 70 kg of TNT?
    - cabalamat 16y ago
      > Is it plausible that a 2 ton vehicle travelling at 40 mph is equivalent to 70 kg of TNT? I helps to know that TNT has roughly one tenth the energy density of petrol (4 MJ/kg v. 40 MJ/kg). If it took 7 kg of fuel just to accelerate a vehicle to 40 mph, vehicles would have to carry vastly more fuel than they do.
Xurinos 16y ago
I pray I never fear to make the decision to save someone's life, all risks reasonably considered. I have been in a similar situation, and I can tell you: your mettle is tested. You have a tiny amount of time to make a decision, so little that it almost comes down to your instincts. You have enough time to make an assessment of what kind of fallout is about to occur for all parties involved, and your main concern is, hopefully, to minimize the damage. Sure, you may not have all the information at hand to make a perfect decision, and few of us can say to have any reliable precognitive power. You have what you always have in life: some information and the ability to make a choice. Let not fear stay your hand. Fear kills as easily as a heart condition. It can always go horribly wrong, but when something appears by sound reasoning to be inevitable, will you have the courage to intervene?
- jgrahamc 16y ago
  Very true comment. I did CPR on a guy in the street a few days ago. I'm sure it wasn't perfect, but I'm now told that the guy didn't die. http://blog.jgc.org/2010/10/you-never-think-youll-have-to-do-cpr.html http://blog.jgc.org/2010/10/you-never-think-youll-have-to-do... In the OP the guy used the information he had to make a fast decision. The toughest thing in the situation I encountered was the moment I realized his heart had stopped and needed to decide right then to take action.
randallsquared 16y ago
"Not to understate his heroism, but had this gone horribly wrong he'd probably be a Darwin award candidate." It's not heroic if the stakes aren't high.