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

Fri Feb 11 17:11:10 AEDT 2011

```> 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.

P.

(are we far enough OT now?)

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