On our TV currently, a well known double glazing company is demonstrating the strength of its product by swinging a 200lb weight against it. The voice-over says “It can withstand being hit by a 200lb weight”.
I estimate that the weight, which looks like a boxer’s punch ball (so soft, rather than hard), swings through about 30 to 40 degrees. The length of the pendulum is hard to guess, but must be at least 20 feet, possibly more. The point of release is equalyy distant from the centre point as the point of impact.
What interests me is the force of the impact, which I judge to be a good deal less than 200lbs.
The question is unanswerable from this information. The total impulse could be calculated, but that’s not a relevant measure of the strength of the glass. The actual force profile depends fundamentally on the rate of deceleration of the weight.
Consider the difference between (1) a 1-lb bean bag dropped on your head from 1 foot up, and (2) a 1-lb rock dropped the same way. The peak force (and thus pain!) you feel is much higher for the rock because it slows down much more quickly than the soft bean bag does.
Vertical drop and surface area of contact … it wouldn’t be hard to videotape this … some of the total force would be absorbed by the soft weight … I might be wrong here but wouldn’t a tempered piece of glass perform this way? … try setting the glass horizontal and place a 200 lbs chunk of gold or tungstun on it … maybe different results …
Yeah, if the points are truly, literally equally distant, then the force (or impulse or energy transfer or whatever else you care to measure) is zero. If the points are just really close to equally distant, then the oomph is really close to zero.
I interpreted the equidistance statement to mean that the system formed a equilateral triangle. Now that I see the ad, there’s all sorts of stuff muddying the waters. Indeed, the support point seems to be many feet away from the window, and the release point a similar distance further from that, so it’s anybody’s guess.
Ah … I believe building code requires the glass in these doors to be tempered … any glazing within 18 inches of the ground/floor … that ball is about a meter in diameter, say 90 kg … so a density of about 0.2 g cm[sup]-3[/sup] … slightly more than cork … [shakes head] … being the guy can’t speak English it’s no surprise this is a total bogus demostration … “Look, I can put a feather on the roof and the building won’t collapse” … woot …