Sedimentology is concerned with the study of sediments and sedimentary rocks. Stokes' Law is a formula that determines the rate of sedimentation by calculating the terminal velocity that a particle will reach as it moves through a viscous liquid. This law states that a particle will attain a constant velocity based on factors like its diameter, density difference with the fluid, fluid viscosity, and gravity. There are three common methods used to measure sedimentation rates: the Atterberg cylinder method, pippete method, and sedimentation balance method.

2.  Introduction
 Sediment grain entrainment
 Settling velocity sedimentation
 1. Atterberg cylinder
 2.pippete method
 3.sedimentation balance.
 Stokes' Law
 Stokes’ Law of settling
 Implications of the Stokes Law

3.  Sedimentology is concerned with the study of
sediments and sedimentary rocks,
 Sediments are defined as a deposit which
settles at the bottom of the liquid.
 Stokes' Law is a formula for determining the
rate of sedimentation. It states that a
particle moving through viscous liquid attains
a constant velocity or sedimentation rate.

4.  A grain starts to move on a planed sand bed when
the combined lift and drag forces produced by the
fluid exceed the gravitational and cohesive forces of
the sediment grain.
 The cohesive forces are applied by finer-grained
sediments only.
 The process of entrainment of grain is mainly
determined by the winter flow velocity and grain
size of the sediments, through shape and
composition of the grains, type or packing of the
sediments and turbulence of the flow are also
important in influencing the entrainment velocity of
sediment grains.

5.  The entrainment velocity versus grain size
plots of hjulstrom (1939)and sunborg(1956)
for sands and gravels respectively,indicate
that behaviour of coarser and finer
sediments are different.

6.  The sediment grain are set into motion,the
transportation and deposition of sediments is
goverened by stokes law which states :
 w= (p1-p) g d
 ---------
 18 µ
 W is the settling velocity,
 p1 & p are density of particle and fluid
respectively.
 G is the acceleration due to gravity
 µ is the fluid velocity
 D is the particle diameter.

7.  It can be inferred from this equation that a
larger particle will settle faster than a smaller
one of equal one of equal density and a denser
grain will settle faster than a than the lighter
one of equal diameter.
 This law is however, valid for a single sphere, so
the shape and concentration of grains will also
influence the settling velocity. to take account
of the grain shape come into force the idea of
sedimentation equivalent particles settling at the
same velocity in water and aerodynamically
equivalent particles in
air(friedman,1961,hand,1967).

8.  Analysis depends on stokes law
 Frictional resistance of a quit sedimentation
fluid upon a sinking spherical particle.
 V= 2 g D1-D2 2
 9 z r
 Where v =particle velocity
 G=acceleration due to gravity=981 cm s 2
 D1=density of a falling sphere,D2=density of
sedimentation liquid
 n=viscosity of liquid
 R=radius of the sphere (cm)
 V=r/t where, R=falling height,t=falling time

9.  D=174.85 n R
(D1-)o2) t
 This method has three important variations.
 1. Atterberg cylinder
 2.pippete method
 3.sedimentation balance.

10.  Atterberg cylinder with an inside diameter of
atleast 5cm & height of 25 to 35 cm,fitted
with siphon which can shut off by a piece of
tubing fitted with clamp.the cylinder is
closed with a ground glass stopper about 3 to
4 cm above its bottom.a ‘cm’ scale is
provided on the wall.
 The 0.063 mm meterial desalted,dispersed
by boiling with h202,dried crushed and
weighed is shaking machine and immediately
transferred to the sedimentation vessel.

11.  After filling water up to desired falling
height ,the cylinder is closed and repeatedly
shaken in a horizontal position and after
setting it up vertically,the starting time is
noted.when the necessary falling time for a
given equivalent diameter is reached.the
glass stopper removed,the clamp is opened
and outflowing liquid is collected and put
into filtering device,it is necessary to begin
with finest grade.
 To separate 2-10 days: 2 to 6.3 =2 days
 And 6.3 to 20=several hours.

12.  Based on changes in the concentration of particles in an
orginally homogenous suspension.several samples at definite
time intervals are collected by placing a pippete immediately
above already deposited material.the quantities of individual
grades are obtained from the change in the concentration of
suspended matter(the determination of dry residue)
 In this method,less time is needed for complete size analysis.
 ANDREAS cylinder (500 cm3 capacity and 30 cm height)fitted
with a 10 cc pippete eith nozzle at zero level end with a
siphoning mechanism is used.
 A time table is calculated from stokes law taking into
account that each pippete samplle reduces the volume of
liquod and therefore the fall height.
 Co=g v1/v2 (g) where 'co' is the weight of the solid matter of
suspension in zero sample (G=weight of weighed sample,V1
=volume of the pippete(10cc,V2=volume of suspension about
500 cc.

13.  Sven oden in 1916 constructed the so-called
"sedimentation balance"whereby grain size
distrubution was determined by continous
weighing of sedimennt material falling on a
weighing pan inside a sedimentation vessel.the
device most commonly used in europe is the
"STARTOUS SEDIMENTATION
BALANCE"CONSTRUCTED by BACHMANN and
produced commercially by the starorious
werke,germany.this automatically plots the
increasing weight of a sediment settling on a pan
against time.the settling height is less and
duration of analysis is faster than other two
methods.

14.  Stokes' Law is a formula for determining the rate of
sedimentation. It states that a particle moving through
viscous liquid attains a constant velocity or sedimentation
rate.
 The rate can be very slow for particles whose density is
close to that of the liquid, for particles whose diameter is
small, or where the viscosity is high.
 Replacing gravitational acceleration with the
acceleration generated by a rotating centrifuge results in
faster sedimentation.
 Centrifugal acceleration can be thousands of times
greater than that of gravity, so the centrifugal
sedimentation rate is thousands of times greater.

15. The following is the equation for Stokes'
Law of Sedimentation:
Vg = d2 (Þp - Þ1) / 18µ x G
where:
Vg = sedimentation velocity
d = particle diameter
Þp = particle density
Þ1 = liquid density
G = gravitational acceleration
µ = viscosity of liquid

16.  The gravitational force pulling the particle
down versus the drag force of the fluid
resisting this sinking.
 The particle will be initially accelerate due
to gravity, but soon the gravitational and
drag forces reach equilibrium, resulting in a
constant “Terminal Fall Velocity”.
 The drag force exerted by a fluid on a falling
grain is proportional to the fluid density (ρF),
the diameter (d) of the grain (in
centimeters), the drag coefficient (CD) and
the fall velocity (V).

17.  High density minerals settle more rapidly
than low density minerals.
 Slow-moving, highly viscous fluids such as
mudflows and density currents can transport
coarser-grained materials than less viscuos
fluids such as rivers and the wind, despite
the normally higher velocity of these less
viscous fluids.

18.  Lower temperatures will increas viscosity
decreasing the fall velocity.
 Because of turbulence, coarser particles fall more
slowly than predicted.
 Non-spherical flakes such as mica will settle more
slowly than spheres with the same density.
 Angular grains will generate small turbulent eddies
that retard settling velocity.

19.  Sedimentology is concerned with the study of
sediments and sedimentary rocks,
 Stokes' Law is a formula for determining the
rate of sedimentation. It states that a
particle moving through viscous liquid attains
a constant velocity or sedimentation rate.
 three important variations.
 1. Atterberg cylinder
 2.pippete method
 3.sedimentation balance.

20.  www.wikipedia.com
 http://members.shaw.ca/gp.lagasse
/Centrifuge%20Training/basic2.html

21. THANK YOU