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Please do NOT attempt to wash the graduated cylinders once they have
oil in them.
Don’t pour the oil in the graduated cylinders back into the big cylinder
until the end of the lab.
Please be sure that the small corks are well seated in the tubes when you
are not measuring the fluid flow from them.
Princeton University
Physics 103/105 Lab
Physics Department
LAB #2: Forces in Fluids
Overview Comments
:
In this lab, you will explore some basic effects of forces in fluids: viscous (frictional)
forces, as well as the buoyant force.
Although the behavior of fluids is rather complicated in general, fluid motion obeys
Newton’s laws.
A small element of fluid can be characterized by its volume, mass, and
characteristic position, velocity and acceleration.
But, the volume can change its shape,
and in the case of compressible fluids, its magnitude can change as well.
In the first two parts of the Lab, you will consider an incompressible fluid, heavy
machine oil, that is very viscous, and in the third part you will consider a compressible
fluid, a gas, but at constant pressure so that its volume does not change.
Do you know that a cubic meter of air weighs almost three pounds?
No wonder it takes
strength to hold your arm out the window of a moving car – it takes force to make all that
air get out of the way!
I.
Flow of a Viscous Fluid in a Circular Pipe
It is a remarkable fact that fluid immediately adjacent to an immobile surface, such as the
wall of a pipe, always has zero velocity.
In order for fluid some distance
y
from the
surface to flow at velocity
v
, a force must be applied:
Av
F
y
where
A
is the area of the surface (or, equivalently, the area of the layer of fluid), and
is
the coefficient of viscosity.
Fluid flow through a circular pipe is slightly more
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complicated.
Poiseuille's law states that for a circular pipe of radius
R
and length
L
, the
pressure difference
P =
F/A (where A =
R
2
) between the two ends of the pipe
required to maintain an average velocity
v
is of the fluid flow over the cross section of
the pipe is related by
4
,
Av
FA
P
R
or equivalently,
4
,
8
R
P
QA
v
L
where,
2
A
RL
is the surface area of the pipe, and
Q
is the volume rate of fluid flow.
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This note was uploaded on 11/23/2011 for the course PHYSICS 101 taught by Professor Asdf during the Spring '11 term at TCNJ.
 Spring '11
 asdf
 Force

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