"Richard Smith" wrote in message ...

"Jim Wilkins" writes:

http://physics.wm.edu/~labs/110/110_pdf/ch4.pdf
If the metal permanently deforms some of the kinetic energy converts
to heat.

Resilient design - make sure that in an extreme event, there's
not-a-lot / no abrupt breaking (low energy and structure is lost) and
a lot of distributed bending and deformation (high energy, and the
structure is still there)... :-)

Job as a welder - repair a height-restriction barrier at a supermarket
http://www.weldsmith.co.uk/dropbox/m...tS_htbarr.html
"Insert plates" so knocking it over again would be a long energy
consuming process.

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A retired town snowplow driver told me that people who erect very solid
steel roadside mailbox stands that don't protect people or property from
damage have been asked to remove them before someone dies.

It's a difficult call, and I would make the part that breaks be easily
replaceable.