[LINK] OT: Speed, acceleration or something else? [WAS] Mobile phone use set to be banned in vehicles - nanny state??

Frank O'Connor francisoconnor3 at bigpond.com
Fri Feb 11 18:18:56 AEDT 2011

OK ... we need to get into Newton's Laws here:

The First lawFrom Wikipedia :

OK .... Let's take the 'rest or uniform motion' thingie. 'Uniform 
motion means inertia. 'Uniform motion' means that every component 
part (be it atom, arm, arse or whatever) of that body is travelling 
at exactly the same speed on exactly the same vector. (In practice 
this doesn't work too well in an environment that includes gravity - 
because that adds another force/vector independent of Newton's Laws 
... but, you get the idea.)

Now this uniform motion/inertia is the cause of everything that 
follows when a car accident occurs ... because it is when the motion 
becomes non-uniform that bad things start to happen. What had been 
the pure kinetic exquisitely vectored energy of mass induced by 
uniform motion suddenly becomes something much less elegant ... 
especially when that energy is now directed on different component 
parts of the bodies concerned in non-uniform ways. Car parts are 
trashed, bones break, flesh tears, softer wet matter tends to blend 
with immoveable objects as the accrued kinetic energy of that inertia 
spends itself at different rates and vectors on different stress 
points ... and if you factor in even more inertia from collision with 
another body travelling at uniform motion well, the effects get even 
more nasty.

Now I find any argument that doesn't agree with the fact that the 
initial inertia(s) caused this damage a tad disingenuous. Inertia 
imparted the energy, inertia was responsible for the vectors of the 
colliding objects, and inertia was responsible for the final state of 
the objects concerned after the energy imparted by the inertia was 
finally dissipated in the final results of the collision.

However else anyone wants to explain it is simply a matter of semantics.

And what Paul quoted there (any action causes an equal and opposite 
reaction) was a paraphrasing of the Third Law.

Now could we get onto something way more interesting that secondary 
school physics. (Dark Matter, Quantum Pairing, String Theory, Many 
Universes etc etc ... come to mind)


At 5:11 PM +1100 11/2/11, Paul Brooks wrote:
>  > At 11:30 AM +1100 11/2/11, David Boxall wrote:
>>>  Is it really speed or acceleration? Isn't it more that, when other
>>>  things change, we don't? Isn't it more accurate to say that inertia kills?
>No - inertia, or more correctly momentum, is measured as mass * 
>velocity.  While in
>motion, the objects have plenty of momentum/inertia, and all is rosy.
>Its the change of motion at the end where the problem lies - the 
>decelleration caused
>by the force imparted by the oncoming object. The force, in turn, 
>comes from Newton's
>First Law (any action causes an equal and opposite reacion)  and 
>through F=m * a, the
>negative accelleration causes a rapid change in velocity, which is 
>manifest as a
>change in kinetic energy (KE=m * v^2). As the kinetic energy is 
>rapidly reduced to
>zero, it is converted (because energy cannot be created or 
>destroyed) into heat
>energy, sound energy and the energy of deformation - with the 
>catastrophic deformation
>of the body and its organs being the thing that kills.
>(are we far enough OT now?)

More information about the Link mailing list