The springs when compressed are under under stress and the molecules are in high tension. The ultrasound waves excite the molecules and can cause fractures. (from a layman in layman's terms.)
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__________________
"I'm a Setter man.
Not because I think they're better than the other breeds,
but because I'm a romantic - stuck on tradition - and to me, a Setter just "belongs" in the grouse picture."
George King, "That's Ruff", 2010 - a timeless classic.
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