[DeTomaso] speaking of wheels falling off--- (Now, head on collision)

Mon Aug 23 01:56:07 EDT 2010

    Kinetic energy is 1/2 MV^2  (velocity is squared).  So a car at 120 has four times the kinetic energy of a car at 60.  But two cars at 60 (closing speed of 120) have a total of twice the energy of a single car at 60.  Momentum is MV, and is useful in some physics problems because the momentum is conserved when two masses join.

    I suppose there is a lot more to this because the cars crush very differently in different collisions, so you'd have to know something about the energy absorbed by the metal deforming.

    The velocity squared term may explain why high speed crashes can be so bad.  

Ken

--- On Sun, 8/22/10, Will Kooiman <wkooiman at earthlink.net> wrote:

From: Will Kooiman <wkooiman at earthlink.net>
Subject: Re: [DeTomaso] speaking of wheels falling off---
To: "'boyd casey'" <boyd411 at gmail.com>, "'Mike Thomas'" <mbefthomas at comcast.net>
Cc: detomaso at realbig.com
Date: Sunday, August 22, 2010, 9:38 PM

I thought we said the same thing.

They crashed 4 identical cars in the show.

The first car hit a wall at 60mph.  It was about what you'd expect.

The second car hit the wall at 120mph.  The car flipped, and crunched the
car about twice as far as the first. The crash was spectacular.  Anyone
inside would have been killed with or without an airbag.

The third crash involved two cars hitting each other at 60mph.  The damage
was almost identical to the first crash, both in the amount of debris and
the compression of the cars.

We were always told in high school that if you hit someone head-on, the
damage is the combined speed.  Not so.  If you hit someone of the same mass
at the same speed (each going 60), you're both going to stop as if you both
hit a wall - at 60.

If you hit a train head-on, you're probably drunk, so who cares.

If you hit an 18-wheeler head-on and both of you are going 60, you have to
deal with the mass of the 18-wheeler, so you're going to get creamed,
literally, whereas the 18-wheeler will have plenty of damage, but he'll
probably survive.

-----Original Message-----
From: detomaso-bounces at realbig.com [mailto:detomaso-bounces at realbig.com] On
Behalf Of boyd casey
Sent: Sunday, August 22, 2010 11:23 PM
To: Mike Thomas
Cc: Will Kooiman; detomaso at realbig.com
Subject: Re: [DeTomaso] speaking of wheels falling off---

So Will and Mike both saw the same show but apparently came away with
different interpretations. Combining the speeds of car A and car b is
simplifying the physics involved for the measurement of energy which is
E=Mass x velocity so if both  cars had the same mass their speeds would be
combined so the statement that I made was essentially correct although
simplified. If one vehicle has substantially greater mass then the other
(like a car hitting a train head on) The car is obliterated and the train
is barely  slowed down. But if two identical masses hit head on and both are
traveling at 60 mph and they are in a vacuum the energy of the impact will
be the equivalent of the energy of one vehicle of double the mass traveling
at 120 mph and hitting a fixed immovable object
In either case I wouldn't want to be in any of the vehicles!  And getting
hit by a wheel and tire coming at you head on at 60 mph would suck. If you
were also traveling in the opposite direction towards the tire and you were
traveling at 60 mph it would suck just as much!

Boyd

On Sun, Aug 22, 2010 at 11:29 PM, Mike Thomas <mbefthomas at comcast.net>wrote:

> The Myth Busters on Discovery Channel did a pretty did a segment on
exactly
> this recently, and also disproved that the impact is equal to the combined
> speed at contact.  Pretty graphic, always done with their slight touch of
> showmanship.
>
> Mike Thomas
>
> -----Original Message-----
> From: detomaso-bounces at realbig.com [mailto:detomaso-bounces at realbig.com]
> On
>  Behalf Of Will Kooiman
> Sent: Sunday, August 22, 2010 6:17 PM
> To: detomaso at realbig.com
> Subject: Re: [DeTomaso] speaking of wheels falling off---
>
> Slightly off topic, but a head-on collision isn't car1 speed + car2 speed.
>
> 60mph car head-on with 60mph car isn't like hitting a wall at 120mph.  It
> was proven very dramatically on myth busters.
>
> I believe it's more complicated than that.  It's has to do with the total
> force.  Car1 speed * car1 weight + car2 speed * car2 weight = total force.
>
> Force applied to car1 = total force/car1 weight.
> Force applied to car2 = total force/car2 weight.
>
> It they're both going 60mph and they're both the same weight, it's just
> like
> they both hit a wall going 60mph.  (assuming they head dead-on, glancing
> blows change everything)
>
> If car1 is 3,000 lbs and car2 is 30,000 lbs (big rig), car1 is going to be
> much worse than head-on, and the 18-wheeler will have much less damage.
>
> I just made up those formulas, but I bet they're correct or at least
close.
>
> BTW, the wheel that went through the windshield was probably going
> effectively 120mph, simply because the windshield wouldn't have slowed the
> tire down much at all.
>
> -----Original Message-----
> From: detomaso-bounces at realbig.com [mailto:detomaso-bounces at realbig.com]
> On
> Behalf Of boyd casey
> Sent: Sunday, August 22, 2010 7:11 PM
> To: Art Stephens
> Cc: JDeRyke at aol.com; detomaso at realbig.com
> Subject: Re: [DeTomaso] speaking of wheels falling off---
>
> I have heard of several incidents where wheels came off of vehicles and
the
> vehicle that lost the wheel did ok but the errant wheel killed the driver
> of
> the car it hit. This has happened more then once in recent memory. The one
> I
> remember more clearly the wheel cam e off a car on an interstate and
> crossed
> the median. As you know the speed in a head on is car +car b + speed of
> impact so a car traveling at 60 mph and a loose wheel traveling at 60 mph
> and bouncing through the windshield and landing smack in someones lap at
> 120
> mph effective speed, it's not a pretty picture!. When I was in college
> (Loyola in New Orleans) I was driving a VW "Super Bug" from my fathers
Ford
> dealerships used car lot when I noticed a VW wheel Passing me on the left!
> The  left rear wheel came off and  the next thing I knew I was sliding to
a
> stop and the wheel was making great time on it's own! Luckily it didn't
hit
> anyone. I was always having problems with the cars that I was given to
> drive
> from the cheapest used car inventory. And every time I had a problem I got
> downgraded to an even cheaper car until finally I was relegated to the
> status of pedestrian!
> Boyd
>
> On Sun, Aug 22, 2010 at 6:43 PM, Art Stephens
> <artstephens at verizon.net>wrote:
>
> > When I crashed my car,  one of the rear wheels with broken upright,
> > half shaft and disc brake assembly attached,  was found days later in
> > a gully about a quarter mile past the car!
> >
> >
> >
> >
> > ----- Original Message -----
> > From: <JDeRyke at aol.com>
> > To: <detomaso at realbig.com>
> > Sent: Sunday, August 22, 2010 12:15 PM
> > Subject: Re: [DeTomaso] speaking of wheels falling off---
> >
> >
> > > I've also had a 'memorable' experience with OTHER PEOPLE'S wheels
> falling
> > > off. Commuting to work one morning in N CA in my modified Corvair, a
> > > cement pumper truck on its way to a job site broke a rear axle
> > > flange off, freeing a gigantic 'flotation' tire, wheel & brake drum
> > > at 50 mph on the freeway.
> > He
> > > was some ways behind me and I saw the accident in my mirrors, but as
> race
> > > announcers say, in heavy traffic 'I had nowhere to go' except to
> > > lean away.
> > > The 250-lb assembly bounced off guard rails and hit my drivers door
> > > a glancing blow that knocked the 2500-lb car sideways half a lane,
> > > in spite of the traction from the same size tires I run on the
> > > Pantera. The wheel
> finally
> > > stopped in the median-strip Oleander bushes. Lucky me- I was the
> > > only
> car
> > > it hit!
> > >  The dent in my car was a foot deep but luckily was confined only to
> > > the door.
> > > A gigantic traffic jam occurred between my banged up car and the
> concrete
> > > truck tipped at an angle across 2 lanes. Once he saw I wasn't hurt
> > > or angry, the truck driver (also the business owner!) was very
> > > apologetic but was MUCH more worried about the full load of concrete
> > > he was to have processed, rapidly setting up behind us in a second
> > > truck (pre-cell phone days). 2 hrs later I drove the beat up car
> > > into work and got no crap about being
> late.
> > > His
> > > business insurance bought me a new door and a full paint job. FWIW-
> > > J DeRyke _______________________________________________
> > >
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