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Re: Impulse

I believe Chuck's point is clearly demonstrated using the happy ball/sad
ball combination with a topple block (TSS#20750) or the sharp and blunt
dart with a topple block (Hewitt) and that is: an elestic collision
transfers more momentum than does an inelastic one, all else being equal.
This is also easily explored using a glider on an air track hitting a force
probe while various materials mediate the collision. With appropriate
software (Vernier, e.g.) the area under the curve stays pretty much the
same but the shape of the curve, and the peak, depend on the choice of
material. Students often begin by saying the dash is padded to make it
"softer" but can be guided by activities like these to consider that it is
by extending the time of the interaction that one saves lives (as list
respondents have pointed out consistently).

At 01:39 PM 10/31/01 -0500, you wrote:
I don't know if it's nuances or old-ances, but MY contribution was
that the first 'safety' padded dashboards (early '50's) were actually
WORSE than the unyielding wood or metal used previously.

The brain, suspended within the cranium, is bruised when the skull is
stopped and the brain continues forward. With the padded/bouncy
dashboard, the brain receives FURTHER bruising as the skull is
bounced backward, on the rebound, making the front of the brain
contact the skull again or perhaps for a longer length of time.



At 12:07 PM -0600 on 10/31/01, Brian Whatcott wrote

I may be missing a nuance, Chuck.
People who make cars want to provide as long a crushing time as possible
between you and the scene of the accident. This minimizes
crushing and piercing forces by spreading the time of application.
One notable design improvement is that the steering column that now
resists impaling your chest by folding, crushing and buckling itself
progressively.

That's my story, at least!

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