(1) The document discusses the myth that the direction of bathtub vortices is determined by the Coriolis effect due to Earth's rotation. (2) It provides background on rotational relative motion and defines the Coriolis effect, which causes objects to veer perpendicular to their velocity. (3) The document argues that the Coriolis effect is negligible for low-speed phenomena like bathtub vortices, and that other factors like the tub's shape are more important in determining the vortex direction.

1. BATHTUB VORTEX MYTH
&
THE CORIOLIS EFFECT
By Kiran Sanjeevan Cabeza

2. OUTLINE
• Introduction
• Rotational Relative Motion
• The Coriolis Effect
• Bathtub Vortex Myth
• Experiment

3. INTRODUCTION
1) The Bathtub Myth
2) The goal of this presentation is to account for the factors
that determine the vortex rotation direction
3) Theoretical Background
• The concept of rotational relative movement
• The Coriolis Effect

4. Rotational relative movement
Velocity & acceleration for P
• V= V’ + wxr
• a = a’ + 2wxV’ + (wxwxr)
The Coriolis Effect The Centrifugal Force can
will always be easily be calculated for any
perpendicular to the given point, it is maximum
object’s velocity. It is on the Earth’s Equator
of the order of (0,033 (m/s-2)) and
magnitude of accounts for only 0,3% of
0,00014·V’ (m/s-2). gravity’s pull.

5. The Coriolis Effect
Because of the Earth’s
rotation, we are all
moving with angular
velocity relative to a
static frame of reference.
Hence, the Coriolis and
Centrifugal accelerations
are introduced.
(Intuitive explanation)
The mathematical
expression for the Coriolis
Force appeared in an 1835
paper by French
scientist Gustave Coriolis.

6. The Coriolis Effect
(N.H.)
(- π/2 ≤ α ≤π/2)
Also due to the cross product, objects
In free fall, objects always tend to
travelling on the Earth’s plane will veer
veer to the East (one can check this
to the right on the Northern
by doing the cross product).
Hemisphere, and to the left on the
Southern Hemisphere.

7. Bathtub Vortex Myth
So when does the Coriolis Effect intervene?
• First considered by Riccioli in 1651 for the deflection of canon balls
• In the formation of tornados
• In the trajectory of missiles
• In other phenomena with high Rossby numbers
Debunking the myth
• The importance of the Coriolis Effect is determined by the Rossby number R(L,V,w)
• Residual disturbance, shape of bathtub, and other factors are much more important
• Experiment

8. CONCLUSIONS
• The Coriolis Effect on Earth is negligible when
dealing with low speed and distance.
• One must always be skeptic when dealing
with popular belief!