[LINK] Mobile phone use set to be banned in vehicles - nanny state??

[Kim Holburn]

On 2011/Feb/10, at 2:19 PM, Antony Barry wrote:

> 
> On 08/02/2011, at 8:49 AM, Kim Holburn wrote:
> 
>> And remember your physics: Speed doesn't kill, acceleration kills.
> 
> 
> Or in the case of accidents the acceleration is in opposite direction to the velocity and damagingly high. The faster you go the higher and more dangerous is the resulting acceleration when you hit a large object. The energy gets dissipated in the vehicle and its occupants and increases at the square of the speed.

Everyone wants to discuss physics? 

It's not true that the acceleration is in the opposite direction of your velocity.

Acceleration is the rate of change of velocity and that can happen in almost any direction.  If you are rear-ended by a car the force on you, the acceleration, is in the direction of your travel.  If you run into something it is in the opposite direction.  If a car hits the side of your car the acceleration is at right angles to your speed.  If you flip your car or roll your car the acceleration is applied at random at different points potentially anywhere on your car.

Actually it's not even your speed but the relative speed of you and whatever you hit.  In a head-on with you both traveling at say 40km the relative speed is 80km.  In a rear-ender it's similarly the difference between your speeds.

The energy released in the collision is the square of that relative velocity times the mass (to vastly over simplify).

But it's still true like I said: it's not the speed it's the acceleration that kills.

Before railways were built people used to think that going at 35 miles per hour would kill you.  That would indeed be "speed that kills" but it wasn't true though and still isn't.


-- 
Kim Holburn
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