Silicon Investor (SI) -- The First Internet Community

STOCKTALK

We've detected that you're using an ad content blocking browser plug-in or feature. Ads provide a critical source of revenue to the continued operation of Silicon Investor. We ask that you disable ad blocking while on Silicon Investor in the best interests of our community. If you are not using an ad blocker but are still receiving this message, make sure your browser's tracking protection is set to the 'standard' level.

Strategies & Market Trends : Booms, Busts, and Recoveries -- Ignore unavailable to you. Want to Upgrade?

To: Raymond Duray who wrote (60762)	3/7/2005 5:02:33 PM
From: Maurice Winn	Read Replies (1) \| Respond to of 74559

Ray, another free physics lesson for you! You lucky lad. <<<then come down a LOT faster than the Twin Towers>> Only if the laws of gravity are suspended. The Towers fell at a rate that essentially matched free fall, i.e. 9.8 M/s/s.> The twin towers fell slower than free-fall speed. That's because wonderful civil engineers put dirty great columns and other structural components into the building. As the building collapsed, it had to crush each layer it ploughed through and accelerate it up to the speed of the layers on top. The momentum and kinetic energy were so great after the top stories started falling through the fire zone that resistance was futile and each layer of resistance was about as effective as Saddam's army in resisting King George II's generals and Poland's cavalry in resisting the Third Reich's panzers. But, there was some resistance. The speed at ground zero was less than would have been the case if a large cannon ball had been dropped from the top at the same time as Windows on the World began its descent. The cannon ball would have arrived first, and been travelling a LOT faster. Note that a small cannon ball [such as a BB gun pellet] would arrive much slower due to air resistance. The resistance is a function of the square of the radius, but the downward force being a function of the cube of the radius - which is also why elephants have big thick legs and antelopes can have spindly little ones. The cross section strength of a leg is the square of the radius, but it's holding up a cubic function. There is also slenderness ratio = a long skinny thing collapses by bending, not crushing. Trees are fairly good at engineering and know this, which is why they have thick trunks at ground level, tapering to a sharp little point at the top. Some trees are very cunning engineers and have even designed themselves to resist avalanches. They have very thick trunks, tapering off quite rapidly to the top, so that when the snow hits, the bending moments are resisted and the tree doesn't fall over. Their branches are also snow resistant [not long and gangly]. Anyway, that's my theory on why the are made like that. But back to the collapsing column of frothing pumice which was shot 10 kilometres high. Pumice has fairly low density, so in free fall through still air, a pumice rock will fall faster than a feather, but a LOT slower than a cannonball, due to air resistance. But when you have 1000 km3 of the stuff going down, there isn't much air resistance [in the same way that following closely behind something else reduces air resistance - which is why aircraft, boats etc, are made long and thin]. Imagine falling from 10 km high instead of Twin Tower height. A person falling those distances is not far off terminal velocity [the maximum speed of fall before being balanced by air resistance]. But a cannonball has a LOT higher terminal velocity so can fall from a LOT higher before reaching balance between air resistance and gravity. 1000 km3 of pumice, falling 10 km, would have a terminal velocity a LOT faster than the Twin Towers falling through resistant columns and air. There's also the sheer quantity of it. 1000 km3 falling 10 km is a very big deal for people in the vicinity. A building falling 0.5 km would have minuscule energy by comparison. But on speed alone, I'd bet on higher speed at ground level by the lightweight pumice coming down, in large quantity, from 10km high. Note that as it leaves the ground for the journey upwards, it must be traveling pretty quickly too, though the expanding column of liquid turning to gas as the pressure is released would make it more like a vast space shuttle taking off, with a long-lasting propulsion system working for quite a few minutes. We could ask Google how long it took the top floor of the two towers to reach ground level and compare that with free fall. A 10 second guess is that it took about, um, let's see...hmm, I'd say about 20% longer than free fall speed. Mqurice

To: Raymond Duray who wrote (60762)	3/7/2005 5:41:12 PM
From: Maurice Winn	Read Replies (1) \| Respond to of 74559

Ray, I've just realized English might be your problem, [or mine], not physics. Maybe you thought I meant pumice in 1000 km3 lots would get from 10 km high to ground level before the top floor of the Twin Towers buildings. I can see that "faster" could mean to some readers "before". But that's a rather obtuse reading of an ambiguity given the situation I was describing and the obvious fact that something [even a cannonball] falling from 10 km would take longer than the few seconds it took for the Twin Towers to completely collapse. <Taupo won't give much warning at all. As the 1000 km3 vast column of compressed liquids turn to gas, it'll fly in minutes to a height of 10 km then come down a LOT faster than the Twin Towers and cause a very large expanding horizontal catastrophe.> Edit: "... of 10 km then hit the ground at a much greater speed than the top floor of the Twin Towers ... etc..." the point was the very large horizontal catastrophe resulting from that high speed descent converted to horizontal expansion on arriving back at ground level. Mqurice