Head-on crash velocities
The following (Dec. 15) is inaccurate:
"a passenger was injured while riding in an Oldsmobile that hit another automobile head on at 50 miles per hour and a combined speed of almost 100 mph"
A head-on with both vehicles (of the same mass) going 50 mph is the same as a vehicle hitting a wall going 50. It will accelerate from 50 mph to 0 mph. Or was this something the lawyer said to juice up the payment? -- Frank Russo
Frank Russo's physics are incorrect. The vehicle hitting an oncoming vehicle will absorb far more kinetic force than the vehicle hitting a wall. See this Math Forum link for an explanation of why. Russo's correct to the extent he means to say that the speed is only one factor in determining how much damage is done. -- Ted Frank
Comments
Note the last sentence of the referenced article:
"On the other hand, if the wall is untouched
and the car absorbs all the energy, then the wall acts like a mirror: the car hitting the wall is just like a car hitting its reflection --
a car traveling toward it at the same speed."
I've seen the results when a car impacts a stone wall at about 50mph. Let's just say that a stone wall acts quite a lot more like a mirror than another car.
Posted by: Doug Sundseth | January 8, 2004 5:30 PM
It's most precise to say that it depends on the wall. For a sturdy stone wall, Mr. Russo will be essentially correct. In my response, I was thinking of two products liability cases I worked on, one where a car tore through a metal fence, and another where the wall of a restaurant was considerably worse for the wear of a car's collision with it.
The larger point--that the combined speed of the cars does convey useful information about the collision, and is not mere lawyer-talk--remains correct. If, heaven forfend, I were to be in a head-on collision, I'm going to be much happier if the other vehicle is going 25 mph than if it were going 50 mph, ceteris paribus.
Posted by: Ted Frank | January 8, 2004 5:56 PM
I wouldn't even try to argue from Frank Russo's stated point. There is clearly a difference between "a passenger was injured while riding in an Oldsmobile that hit another automobile head on at 50 miles per hour and a combined speed of almost 100 mph" and "a passenger was injured while riding in an Oldsmobile that hit another automobile head on at 50 miles per hour and a combined speed of almost 55 mph".
My only point was that I thought you mischaracterized the link in your response.
To a fairly large extent, my decision to respond was informed by the wreck of a car that had actually run into a wall at 50 mph (and to which I alluded in my response.) The street turned right, the (intoxicated, IIRC) driver didn't, and the car's engine ended up in the back seat. The wall was barely scratched.
The reason I know about it is that the car was left on the lawn in front of the base exchange (the crash was near an air base in Germany) for several days as a reminder of the dangers of drunk driving. It has certainly reminded me over the years. I often think about this cautionary event when driving on icy roads near big trees, bridge abutments, and oncoming traffic.
Posted by: Doug Sundseth | January 9, 2004 3:37 PM
Make a brick wall (that is unmovable). Crash two Olsmobiles into each side of it at the exact same time, both going 50 Mph. How it this different from the head on?
Thank you,
thank you very much
(puts on cape and leaves the room)
Frank Russo
Posted by: Frank Russo | January 10, 2004 5:02 AM