Do you fasten your seatbelt for every journey?.....really?......I don't

Flyboy152

You really need to take a chill pill. All of that because you don't understand maths. Geez.

bigjl

Gloomendoom wrote: »

The car hitting the wall at 60mph would do so twice as hard as two cars hitting each other at 30mph.


A 2 ton car traveling at 60mph would hit a solid wall with a relative impact energy of 3600

Two 2 ton cars both travelling at 30mph and hitting each other head on would do so with a combined relative impact energy of 1800.

This is because the energy increases as the square of the speed.

E = (1/2) mass × (speed x speed)
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Very nice, but irrelevant to the thread.

The comment that Flyboy and his mate didn't like was

"A 60 mph impact against a wall will have broadly the same "Mechanism of Injury" as a collision between two objects doing 30mph.

I will believe what I have seen and been taught rather than a TV program to be honest."


This is what i stated, and it is still true, note the word "BROADLY", in other words not exact, not accurate, you now an approximation.

I know you science type blokes like your things exact and measurable, but sadly life isn't like that, there are no absolutes, somebody might fall 50 ft and only break a nail, somebody might fall the same 50 ft and break hit back, neck, pelvis and both femurs.

Both would be judged to have experienced the same " mechanism of injury", you wouldn't consider wind shear, humidity, time of day or barometric pressure. The only relevant factor would be the fall and the patient treated accordingly, regardless of wether they have much pain or not, they are treated as the worse case scenanrio until the Radiologist says otherwise.

If you can't take the comment in the way it was intended then I feel a little sorry for you to be honest.

And Flyboy, no the thread is about not wearing a seatbelt, then progressed onto injuries that can occur when not wearing a seatbelt when involved in an accident.


You are the !!!!!! that tried to make this a thread about physics etc.

If you want to discuss such a thing in the broad context of an RTC then please feel free to start a new therad, I will read it intently, as yes all the theory is interesting to an extent, it is always better to have more knowledge than less, but if you can't see why it is irrelevant to assess a simple RTC to the level you want to is irrelevant in the context of this thread then I advise you need a holiday, always thought that some of the "Engineers" at Uni where a wound a bit too tightly.

bigjl

Flyboy152 wrote: »

You really need to take a chill pill. All of that because you don't understand maths. Geez.

I understand Maths, studied it to Higher and there was some on the first year of my degree, but I found it boring.

Not my fault if you can't understand a simple thing like "mechanism of injury" now is it.

Always wondered what happened to the spotty kid with his head in the books and no social skills, would seem he posts on forums about technical terms that mean a lot to him, but nothing to others, I could do so myself, lots of funky terms used by Paramedcs these days, but then why would I do that. Though I did think mechanisim of injury was actually a simple concept. Never expected it to confuse a sharp scientific brain like yours.

Isn't that a bit like trying to say a Premiership Footballer is stupid because he doesn't understand Rugby.

Which is what you have tried to do

stevemcol

Gloomendoom wrote: »

The car hitting the wall at 60mph would do so twice as hard as two cars hitting each other at 30mph.


A 2 ton car travelling at 60mph would hit a solid wall with a relative impact energy of 3600

Two 2 ton cars both travelling at 30mph and hitting each other head on would do so with a combined relative impact energy of 1800.

This is because the energy increases as the square of the speed.

E = (1/2) mass × (speed x speed)
.
.
.
.

Incorrect.
30+30=60
and 60 = 60

Speeds are the same. The variable is deformation of the two cars versus the solid wall / tree.

mikey72

Gloomendoom wrote: »

The car hitting the wall at 60mph would do so twice as hard as two cars hitting each other at 30mph.


A 2 ton car travelling at 60mph would hit a solid wall with a relative impact energy of 3600

Two 2 ton cars both travelling at 30mph and hitting each other head on would do so with a combined relative impact energy of 1800.

This is because the energy increases as the square of the speed.

E = (1/2) mass × (speed x speed)
.
.
.
.

That equation only works for rigid bodies, and a car isn't rigid.
Having said that, the closing velocity of the two cars is 60mph, so apart from the rigid bit, the total energy in the sytem is the same.
There will be less damage, marginally, as the two cars will crumple, and expend energy in two crumple zones, whereas with one car and a wall, you'll only expend energy in one crumple zone, the wall is a truly rigid body. (Assuming you don't knock it over)

Two cars each hitting a solid wall at 30mph would do half the damage (to the wall) of one car at 60 though.

alastairq

Two cars each hitting a solid wall at 30mph would do half the damage (to the wall) of one car at 60 though.

to be fair.. the wall will likely fall down in both instances....which is all the owner will care about?

Oh..and how far they have to search to pick up the bits?

Gloomendoom

stevemcol wrote: »

Incorrect.
30+30=60
and 60 = 60

Speeds are the same. The variable is deformation of the two cars versus the solid wall / tree.

Gloomendoom

mikey72 wrote: »

That equation only works for rigid bodies, and a car isn't rigid.
Having said that, the closing velocity of the two cars is 60mph, so apart from the rigid bit, the total energy in the sytem is the same.
There will be less damage, marginally, as the two cars will crumple, and expend energy in two crumple zones, whereas with one car and a wall, you'll only expend energy in one crumple zone, the wall is a truly rigid body. (Assuming you don't knock it over)

Two cars each hitting a solid wall at 30mph would do half the damage (to the wall) of one car at 60 though.

Using my figures and assuming all cars have identical crumple zones each car crumple zone will have to dissipate 900 in the 30mph head on crash.

The car hitting the wall will have to dissipate 3600 through its single crumple zone.

The odds on the wall driver are getting worse.

stevemcol

Gloomendoom, don't take it too badly. We all make mistakes

bigjl

So the, admittedly basic, way I have been taught to assess possible forces in an RTC is correct then?

Which since it is the way it is done world wide I assumed it would be.

We where told to mainly focus on the speed of the vehicles involved, and the direction of travel.

So a vehicle travelling at 30 mph, hit from the rear by a car doing 60mph tends to have a similar "mechanism of injury" as a car that is hit from the rear whilst stationary by a car travelling at 30 mph.

The old adage from one of my trainers used to be KISS, Keep It Simple or look Stupid.

Just reread DoomandGloom's comment, yes that is completely wrong, should have looked closer.

His thinking is surely completely flawed as the objects are going in opposite directions and therefore you need to add the two figures together, not average them as he has done surely.