Previous topic: Gravity Physics 152 Home Page Next topic: Some Useful Math

# Physics 152: Lectures on Fluids

*Michael Fowler, UVa.*

*PDF of complete set of fluids notes.*

## Lectures

*Beginning with Archimedes jumping out of a
bath and running down the street shouting "Eureka" because he'd realized how to
prove an expensive crown wasn't all it seemed, going on to his Principle of
buoyancy and the concept of pressure, then to the much later realization that
we live in an ocean of air with its own pressure, finally to Jefferson
measuring the altitude of Monticello with a barometer bought in Philadelphia in
1776.*

Boyle's Law and the Law of Atmospheres PDF

*How Boyle established
his famous Law PV = constant at constant temperature, and how we can use it to
discover just how the atmospheric pressure decreases with altitude.*

*Contrary to most
peoples' intuition, when fluid flowing through a pipe encounters a narrower
section, the pressure in the fluid goes* down*. We show how this must follow
from Newton's
Laws, and demonstrate the effect.*

Liquid Viscosity and Gas Viscosity PDF

*After briefly
reviewing friction between solids, we examine viscosity in liquids and gases, building
up some understanding of what's going on at the molecular level. This makes it possible to understand some
surprising results: for example, the viscosity of a gas *does not change* if the gas is compressed to greater
density.*

*We present the
calculus derivation of the smooth flow patterns for a wide river and for fluid
in a circular cross-section pipe, and find the total flow for given slope or
pressure drop.*

*M, L and T: all
physics equations must have the same dimensions on both sides.This can be exploited to arrive at some
interesting predictions without doing much math—for example, that the smooth
flow rate through a circular pipe goes as the* fourth* power of the radius.*

*Dropping a small ball
through a very viscous fluid: a dimensional prediction of the dependence of
speed on radius, and an experiment with glycerin.*

Inertial Drag Force and the Reynolds Number PDF

*Another experiment,
this time dropping coffee filters through air, with a very different result: but
also predicted dimensionally! The
Reynolds number: the dimensionless ratio of inertial drag to viscous drag.*