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Physics explanation sought

uruk said:
Pssst, They have taken pictures of atoms:
http://www.aip.org/history/einstein/atoms.htm

Well, really the electron shell.

Sorry, carry on!
Click to expand...

[pedant mode]
The image was made by a Scanning Tunneling Microscope, a device that "feels" the cloud of electrons that form the outer surface of atoms, rather as a phonograph needle feels the grooves in a record.
Click to expand...
See! See! It's interpreting the atom, not really photographing it!
[/pedant mode]
:boxedin:
 
they have taken pictures of atoms

atomant2.jpg
 
TruthSeeker1234 said:
Hans is right. The wind is blowing from left to right in the picture. The dust which has been in the air the longest will have blown the farthest.

It is a very simple explanation.

Any talk about "non uniform distribution of debris" is completely irrelevant gobbledy-gook. Gravy, and others, you are so habituated to obfucscating and confusing everything that you did so here without stopping to think.

Gravy, read what Hans wrote, and compare that to what you wrote. Hilarious.

I still would like to see a video from the west, and have not found one. Anybody know of one?
Click to expand...


I don't even mention the non-uniform distribution of debris until the 5th paragraph my longer post above . In the first 4 I address the motion that the wind would impart to debris.

Even less than 10 meters since the effect of the wind will not be immediate (due to inertia of the object)
The side force on an object is equal to the drag force which is proportional to the velocity of the wind relative to the object. The object initially has a sideways velocity of zero and only that drag force(air resistence) can give it any sideways movement. That force will then acellerate the object , as it starts to move the velocity of the wind wrt to the object becomes less and so the force pushing it sideways becomes less also and so its sideways acelleration becomes less as well. The object will eventually approach the same ground speed as the wind though it will never actually acheive the same velocity as the wind.
Click to expand...

I forgot to add that the acelleration of any object under a drag force of a wind will be inversely proportional to the object's mass. Thus lighter objects will gain velocity quicker than heavier objects.

Let's do some calculations shall we.(one could probably note TS1234's eyes glazing over at the very thought of doing any math let alone being able to grasp the concepts involved)

let's assume a particle with a diameter of 10 microns, which falls into the size range of silt. If we assume a density of 2700 kg/m^3, which is fairly typical of rocky material, we can calculate the mass of the particle,

volume of a cube of 10 microns is

vol = (10-5)3 = 10-15 m3
m = vol*density = 10-15 m3*2700 = 2.7 x 10-12kg

The cross-sectional area of the particle is,

A = (10-5)2 = 10-10m

The drag force is (Cd*rho*V^2 )(0.5)
Cd= coefficient of drag = 2.1(for a rough rectangle)
rho=density of air = 1.225 kg/m3V=velocity = 5 MPH = 2.25 m/s
A=area in the plane perpendicular to the direction of travel = 1X 10-10 m2



From above, the drag force on a particle is given by,

Fd = Cd*rho*A*V^2/2

Fd = 2.1(1.225)(10-10)(2.25)2(0.5)
= 6.5 X 10-10 kg-m/s2 (Newtons)

Since F=ma we can now deduce the acelleration of this dust mote under the influence of a 5 MPH wind.

6.5 X 10-10 kg-m/s2 = (2.7 x 10-12kg)a

a= 6.5 X 10-10 kg-m/s2/2.7 x 10-12kg
a= 240 m/s2
Under a constant 5 MPH wind creating this force the dust mote will get to 5 MPH in a little over 1/100th of a second
Doing the calc for an object 1000 times larger(still small at 1 centimeter) it will have a mass 0.0027 kg and an area of 0.0001 m2
Fd= 2.1(1.225)(0.0001)(2.25)2(0.5)
6.5X 10-4a=0.024 m/s2
It will take over 10 seconds for this object to reach 5 MPH under a constant 5 mph windspeed, which doesn't occur since its windspeed decreases as soon as it starts moving along the same direction as the wind, so it will take longer than 10 seconds for a 1 cm cube of concrete to get to 5 MPH.

I used a cube as representing the shape of the particle. If you want to use a sphere for comparison you can pretty much halve the Fd and therefore halve the acelleration and therefore double the time.

The above also is a great simplification of the situation at the towers during collapse. The collapse itself would have denser objects falling faster than the less dense objects which would reach terminal vertical velocity quickly. The falling dense objects would be causing a downward draft thus drawing the air downward and interrupting that 5 MPH wind.

TS1234 is invited to check my calculations (for that matter I absolutly WANT other people to) and to calculate the wind force on a square steel column section measuring 60 cm wide by 5 meters long and the acelleration that it would then impart on that column piece.
 
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TruthSeeker1234 said:
I am wondering why the material in the OP pic, which is dense concrete dust, and whatever else, is drifting northward as it falls. What force is present to cause this?
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Get your terms right.

Not dense. Dust is not dense. It is called dust since it is a scattering of very small particles injected into a large volume of another material, in this case a fluid called air.

Not drifting. Try propelled asymetrically outward by air pressure, whose kinetic (impulse) energy derives from the collapse of 80+ stories in rapid succession of a very large building. The air compression can be simulated by holding your right hand above your left hand. Fill you left hand with pepper, to simulate dust. Clap down hard. Note the dispersion of dust.

Do the same with talcum powder. Note the dispersion.

Now, go clean up that mess, young man, and don't let me catch you doing that in the kitchen again.

DR
 
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Darth Rotor said:
Get your terms right.

Not dense. Dust is not dense. It is called dust since it is a scattering of very small particles injected into a large volume of another material, in this case a fluid called air.

DR
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[more pendantry]
........how about, a large quantity of fine particulate matter with a relatively small mean square distance of separation between individual particles.[/pendantry]

(gawd, I hope 'pendantry' is a real word.):D
 
Do the same with talcum powder. Note the dispersion.
Click to expand...
Try again with sawdust and then with dry sand. In each of the four cases use the same volume of material.
Make note of the percentage of material(by volume), in each of the four cases, that remains in your hand. Determine the density of the particles in each case.
Plot density vs. percentage of material ejected.

Re-run the experiment two more times first using a faster clap and then a slower clap than the original experiment, and plot the results. Compare each graph and draw conclusions.
 
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