huangyhg

falling brick problem
could someone tell me how to calculate the force of a brick falling 30 feet and what kind of damage i could expect on 2 layers of plywood? the plywood would be used to protect some translucent fiberglass roof panels.
f=ma and then use the force as an impact load, analyzing the plywood in sections as a skinny beam.
"force" doesn't really apply ... the brick will hit at some velocity (not hard to calc ... potential energy = kinetic energy), so it'll some impulse (=mv) which the pylwood will absorb over some (small) time period. i'd expect the plywood would absorb the energy of the brick by bending.
part of the problem is does the brick hit end on or side on (less severe, as the energy of the brick is distributed over a larger area of plywood)
it turns out the brick is a "speedbrick" that is 8"x12"x3.2" and it weighs 4 pounds. the worst case would be landing on the 8"x3.2" side.
no, the worst case is that is lands on the short edge.
the time period of the force action is very short (0.01 sec?, maybe less). so assuming or calculating a velocity deals with instanteous acceleration, to determine f=ma.
i strongly recommend you try to get a brick cannon built by your company for testing. in the name of safety, of course!
-- mecheng2005
actually...the worst case is landing on a corner!
landing on the corner is worst case, (point load).
arh, you don't need a "brick cannon" ... just a 30' crane, or toss the brick off a 4 storey building ... i'd put up some netting (cricket nets ?) 'cause the damned thing could bounce somewhat !
send the brick to texas tech.
they have an air cannon they use to shoot 12' long 2x4s @ 125 mph at walls to determine the wall sections acceptable to prevent penetration. - it has got to be a lot of fun doing it!
dick
why go to the expense of calculating when you could actually do it as a previous response said.

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