Engineers and
Scientists Third Edition
Ohanian and Markert
I have never been able to understand why I have been granted the ability to understand geo-physics. I asked god for the ability to understand things but I am foul mouthed and have a lurid past I'd rather not discuss. So I have no right to get things that more adept and better taught people some of whom are, or were, well paid experts.
The thing is that being maths blind forced me to explaing things in a way that i can undestand and if I can understand it then so can everyone else.
Consider this insight and my failure at maths:
Page 19 discusses decimal points and the authors use a brilliant fligh of insigth to do so. But they are explaining methematical concepts rather than simplifying the physics for dolts like me.
We can obtain a rough estimate of the size of a molecule by
EXAMPLE 5
means of the following simple experiment. Take a droplet of
oil and let it spread out on a smooth surface of water. When the oil slick attains
its maximum area, it consists of a monomolecular layer; that is, it consists of a single
layer of oil molecules which stand on the water surface side by side. Given that
an oil droplet of mass 8.4 10 7 kg and of density 920 kg/m3 spreads out into
an oil slick of maximum area 0.55 m2, calculate the length of an oil molecule.
SOLUTION: The volume of the oil droplet is
[mass]
[volume]
[density]
8.4 10 7 kg
10
9.1 10 m3
(1.11)
920 kg/m3
The volume of the oil slick must be exactly the same. This latter volume can be
expressed in terms of the thickness and the area of the oil slick:
[volume] [thickness] [area]
Consequently,
[volume]
[thickness]
[area]
9.1 10 10 m3
1.7 10 9 m
(1.12)
0.55 m2
Since we are told that the oil slick consists of a single layer of molecules stand-
ing side by side, the length of a molecule is the same as the calculated thick-
ness, 1.7 10 9 m.
Optical recognition and Blogger have a long way to go and so has Linux:
Estimate of the size
of a molecule:
An oil slick of 0.55
square metres is one molecule thick.
If the oil weighs
8.4 x 10^-7 kg and has a density 0 920 kg/m3 spreads out into a layer
one molecule high. The height of a molecule is:
Volume = Mass /
Density
The volume and depth
of the oil (if even) is: Volume = Thickness x Area
Consequently,
Thickness = Volume / Area
I am not sure how
they would know it spread out evenly but it is still a quick and
reasonable approximation. But why not use simple round figures?
(They are insisting
on showing mathematicians how to count, so we have to render it for
us dullards.)
9.0 x 10^-7 kg has
a density 0.90 kg/m3 has a slick of 0.50 square metres one molecule
thick. Assuming spherical molecules; each one is: 1.7 x 10^-9 m. according to their figures
Is
that 0.00000000017?
Not that I am
equipped to look nor that it matters greatly. But it is nice to know that quantum mechanics can be quite simple.
