fluiddynamics

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Another example of the magic of fluid dynamics: laminar flow.

Laminar flow occurs when individual layers of a fluid remain distinct from one another even while undergoing motion. Laminar flow is observed within a specific regime or for a specific set of velocities (and momenta) of the fluid. The factors related to this specific regime of fluid dynamics depend upon the density and viscosity of the fluid.

What the makers of this video have done is made a cylindrical container which has a hollow region and within this hollow region is another cylinder. In the hollow region they’ve placed clear corn syrup and in order to demonstrate the non-mixing (non-diffusive, non-convective) nature of laminar flow they have placed three different colors of corn syrup at different radial points in the clear corn syrup. When they crank the inner cylinder they rotate the corn syrup within the regime of laminar flow. You can see the bands of died corn syrup spread around the cylinder.

Watch what happens when they reverse the direction of the crank.

Moar excitement!!

In this image the flow around a baseball is visualised using smoke and UV light. The baseball is moving from right to left and spinning in a clockwise direction.  The change in the fluid flow due to this rotation gives rise to the swerve found in many ball sports and has come to be known as the Magnus effect. Here the flow separates earlier on the bottom of the ball than on the top causing a difference in pressure which gives rise to a force upwards.. 

There was controversy in 2010 at the FIFA world cup when the ball used, the Jabulani, did not behave in the way players were accustomed to.  Various factors, such as surface finish, can alter the flow seen in the picture above which will alter the swerving characteristics of a ball.