Civil and Environmental Engineering 2224 Study Guide - Fall 2018, Comprehensive Midterm Notes - Page 3, X Window System, Variance
12 Oct 2018
School
Department
Professor
Civil and
Environmental
Engineering 2224
MIDTERM EXAM
STUDY GUIDE
Fall 2018
T = tangential (tangent/parallel to a body at a point)
N = normal (normal/perpendicular to the body at a point)
Divide each of these forces by the area upon which they are acting.
This is a stress. Remember materials? Stress = F/Area
Lecture 1
September 11, 2018
1:37 PM
Lecture Notes Page 1
find more resources at oneclass.com
find more resources at oneclass.com
So, because we have this problem that we can't determine any finite properties, we
have developed an assumption in order to help us solve fluid mechanic problems.
If the problem dimensions are much larger than the spacing b/w molecules,
we can take the properties of a fluid at a point as being the average of a very
large number of molecules surrounding that point
We look at the physical dimensions of the problem we are trying to solve relative to
the spacing between individual molecules
This assumption allows us to treat fluids as a "continuum" with properties that vary
continually and smoothly. This allows us to calculate
"Smoothly" in the sense that the density shift is consistent and predictable. At one
large enough point it can be assumed to be lets say 5000 molecules in 1 m (with
only slight variance because if there is 5 000 molecules it will be varying between 4
990 and 5 010, so we can assume 5 000), then the density at another point can
4000 molecules in 1m... Then 2500... Or whatever. All it says is that this allows us to
treat the fluid as a gradual and predictable shift in density throughout the fluid and
thus we can use this to predict properties we'll see next lecture.
Mean free path for a molecule: The distance a
molecule will travel before hitting another
molecule.
(A way of thinking is: its a measure of how
much space there is in the particular fluid)
Mean free path for a molecule is given by:
λ = . m/pd2
m = mass of molecule (kg)
p = density (kg/m3)
d = diameter of the molecule (m)
For example, air at the earth's surface
λ = (. * .8 x26) / (123)(3.7 x 10-10)2
Lecture Notes Page 2
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
T = tangential (tangent/parallel to a body at a point) N = normal (normal/perpendicular to the body at a point) Divide each of these forces by the area upon which they are acting. So, because we have this problem that we can"t determine any finite properties, we have developed an assumption in order to help us solve fluid mechanic problems. We look at the physical dimensions of the problem we are trying to solve relative to the spacing between individual molecules. If the problem dimensions are much larger than the spacing b/w molecules, we can take the properties of a fluid at a point as being the average of a very large number of molecules surrounding that point. This assumption allows us to treat fluids as a continuum with properties that vary continually and smoothly. smoothly in the sense that the density shift is consistent and predictable.
