It very much depends on exactly what you're trying to state with your
measurement.  If, for instance, you wanted to say that your tempered
glass, properly mounted, could withstand certain impacts you'd follow
what most of the industry does and simply state that it can withstand
the impact of a 1" diameter stainless steel ball from a height of 1
meter (or something similar depending of how good your glass really
is).

If you're talking about electronic components you'd usually mention
that your product is capable of handling an acceleration, for instance
it might work after being "hit" with an acceleration of 5,000 G's over
a period of not more than 5 milliseconds, and 50G during operation
indefinitely.

The nice thing about G measurements is it removes the mass and point
of impact from the equation - you get to figure those out based on the
environment.  This is useful if you're attaching your device to a car,
for instance.  In fact ECU modules experience greater impact dropping
from a worker's hands and hitting a concrete floor than they do
installed in the car and involved in a crash.

There is no single unit that encompasses all of the factors you
mention that I'm aware of, and if it exists it would really have a
very narrow application and be prone to manipulation, much like the
EPA mileage numbers.

For instance, you couldn't make a number (neckles) that accounts for
the particular deformation that occurs in both the glass and the ball
that is linearly related between a steel ball and a copper ball.  The
copper ball, being less dense, would be larger and have a larger
surface area for a given mass.  Or trade that out for a lead ball
which is more dense, and smaller, but deforms more readily.  A single
number couldn't account for all three types of contact.

It's hard to compare apples to apples without a common measuring
system, and most industries have developed standard test setups for
their products, but you'll be hard pressed to find out if an
electronic component can take the same blow as tempered glass merely
by looking at the data sheets and converting both to this same magic
neckles number.

-Adam

On 7/23/08, Tom=E1s =D3 h=C9ilidhe <toe@lavabit.com> wrote:
>
> What kind of units do you use in physics to describe how hard a smack
> something got, or how hard a smack something can sustain?
>
> I mean let's say you're selling tripple-glazed windows, and you're
> marketing them as being "virtually indestructible". Your ad for them
> might say that they can sustain a smack as high as 400 neckles. I'm just
> wondering what a "neckle" would be? Would it be force? Or pressure? Or
> impulse?
>
> Let's say there's a golf ball whose mass is 50 grams, and it's moving
> through the air at 200 metres per second, and let's say it hits one of
> these windows.
>
> Speaking more from human intuition rather than a knowledge of physics,
> it seems to me that you've to take into account the following in order
> to determine just "how hard a smack" the window got:
>    * The mass of the golf ball
>    * The speed of the golf ball
>    * The hardness of the golf ball
>    * The surface area of impact
>
> Well the momentum of the golf ball is 200 x .05   =3D   10 N s
>
> Let's say that the golf ball's made of titanium. Titanium has a hardness
> of 6 on the Mohr's scale.
>
> I don't know how you'd calculate the impact surface area seeing as how
> the golf ball is a sphere... hmm... but anyway, is there any sort of
> unit that gives you an idea of how hard a smack something got? It's be
> cool to be able to say "the helicopter crashed into the building with
> 1700 neckles".
>
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