0Introduction
IB Fluid Dynamics
0 Introduction
In real life, we encounter a lot of fluids. For example, there is air and water. These
are known as Newtonian fluids, whose dynamics follow relatively simple equations.
This is fundamentally because they have simple composition — they are made
up of simple molecules. An example of non-Newtonian fluid is shampoo, which,
despite looking innocent, has long chain molecules with complex properties.
In fluid dynamics, one of the most important things is to distinguish what is
a fluid and what is not. For example, air and water are fluids, while the wall is
solid. A main distinction is that we can lean on the wall, but not on air and
water. In particular, if we apply a force on the wall, it will deform a bit, but
then stop. A finite force on a solid will lead to a finite deformation. On the other
hand, if we attempt to apply a force onto air or water, it will just move along
the direction of force indefinitely. A finite force can lead to infinite deformation.
This is the main difference between solid mechanics and fluid mechanics. In
solid mechanics, we look at properties like elasticity. This measures how much
deformation we get when we apply a force. In fluid mechanics, we don’t measure
distances, since they can potentially be infinite. Instead, we would often be
interested in the velocity of fluids.
There are many applications of fluid dynamics. On a small scale, the dynamics
of fluids in cells is important for biology. On a larger scale, the fluid flow of
the mantle affects the movement of tectonic plates, while the dynamics of the
atmosphere can be used to explain climate and weather. On an even larger scale,
we can use fluid dynamics to analyse the flow of galactic systems in the universe.