Part II Limericks
In 2001 for the last time, I gave the Cambridge Part II course on Fluid Dynamics. I terminated every other lecture with a limerick summarising its content. Here is a somewhat edited version:
You know that in moments of stress
You tend to get tenser, not less;
But since stress is a tensor
You needn't feel denser;
It's tricky, I have to confess.
Stress is related to strain;
Surely that's perfectly plain!
But please don't neglect
The viscous effect,
For this makes the energy drain.
The equation of Navier-Stokes
Describes flow of egg-whites and yolks;
But now take the curl,
This will please any girl,
And may satisfy even the blokes.
Profiles of speed parabolic
Are common in channels hydraulic,
In pumping of blood,
In sliding of mud,
And in suction of drinks alcoholic.
The spreading of honey on toast
Is a task that gives pleasure to most;
But the pressure's unbounded
In corners not rounded,
So take care if you are the host!
You need to be fairly astute
To track flow in a corner acute;
Though creeping and steady
There's many an eddy,
Too many by far to compute!
A sphere near a vertical wall
In Newtonian fluid will fall
Under modified weight
With proportional rate,
But sideways it won't move at all.
When two fluids flow in collusion,
You'll observe a degree of intrusion;
The reason is clear,
But branching may lead to confusion.
Production and spread of vorticity
Is a matter of utmost simplicity;
Near a boundary, say,
It can't get away,
In a flow of well-crafted complicity.
Flow past a cylinder bluff --
Surely that's easy enough?
But flow retardation
And that's where the going gets tough!
I'll show you as well as I'm able
That a vortex sheet is unstable;
The behaviour's erratic,
The growth rate's dramatic,
And the problem gets most disagreeable!
Let's study the rise of a bubble;
Some really go at the double;
With spherical cap
Some get in a flap;
You can see them without any trouble.
The end of this course is now nigh;
You'll anticipate this with a sigh!
But please recollect,
Whether prone or erect,
There are plenty more problems to try!