TAYLOR CURTAIN: Record Turntable
Purpose: To introduce an aspect of geophysical fluid flow, or world ocean flow due to
the earth’s rotation.
Background: Besides the apparent deflection in travel of large fluid masses in a rotating
system due to the Coriolis Effect and the related effect when winds act upon ocean waterEkman transport, another phenomenon tied to the earth’s rotation is that of Taylor
curtains. (Sir Geoffrey Taylor, 1886-1975, was one of the great scientific minds of the
20th Century. His major contributions were in fluid dynamics. It is said he first predicted
this phenomenon theoretically in the 1910s, and then was so disbelieving went and set up
the demonstration. He was an avid tinkerer.) If a volume of water is spun up to a fixed
rotation rate for long enough to have all the liquid rotating at the same velocity, then it is
called “solid body rotation”, a sort of ideal state. Though this is a laboratory situation, it
leads into the general discussion of the earth’s rotational effects upon ocean water. Some
of these behaviors can be unexpected, provoking further interest in physical
oceanographic circulation.
Materials: Operational but surplused record turn-table
2 large c. 4 liter round transparent water bowls
Large bucket or bowl to refill the above
Food coloring
Tape, paper, marker
Screwdriver
Procedure: 1) Tape a sheet of paper on to the turn-table. Mark the exact center of the
turn-table on to the sheet.
2) Place the bowl on the turn-table and turn on to 45 rpm.
3) With a hand placed on the turn-table deck, take the screwdriver in the other hand and
rest it on the first hand as if it were a “tool-rest guide”. Place the screwdriver tip against
the rotating bowl’s side and gently center the bowl using this arrangement. It’s centered
when the bowl has been shoved to that position where the sides are always just in contact
with the screwdriver tip. Mark the bowl directly above the paper center mark you see
through the bowl.
4) Half-fill the bowl with water.
5) Give it 2-3 minutes to come to a uniform rotation.
6) Repeat step 4 for a bowl just sitting on a table (best if it has been sitting covered for an
hour or so).
7) Ask for predictions from students how a drop of food-coloring dropped midway
between the center and wall of each of the two bowls will behave.
8) Do it and discuss the different behaviors observed. Have students look both down
vertically and in from the sides.
9) Again ask for behavioral predictions, this time for turning off the rotation.
Discussion: The still bowl shows the food coloring drop sinking due to its higher density
relative to the water. (There may be a slight surface film dispersion due to surface
friction at the air–water interface.) Spirals of food coloring whirl off as the drop
descends, beginning the dispersion at all depths that can take hours.
The drop into the rotating water mass also descends in a similar manner initially,
but then it stays in the same vertical plane due to differential shear forces (the rotational
velocity increases with distance from the center). This shearing elongates the coloring
into a stable vertical band or curtain. It sometimes moves in or out from the center
creating a spiral.
(Infrequently, sharp-eyed observers may see a very thin film of food coloring
migrating inwards or outwards once it reaches the base. This is a basal boundary layer of
Ekman transport.)
Upon cessation of the rotation, the curtain continues to rotate due to the angular
momentum of the water. As friction begins to slow down the spinning water, the spirals
enlarge, metamorphose into eddies and eventually break up into irregular flow that slow
down more and more until they stop.
Source: Adapted from pp. 4 and 14 in Benoit Cushman-Roisin, 1994, Introduction to
Geophysical Fluid Dynamics, Prentice-Hall, Englewood Cliffs, N.J., 320 pp.