THE OLD BUSHMAN’S WATERFALLS

Example of rapid of French Guiana

Summary:I. Fauna and flora of the waterfalls

II. Two persons missing at the Old Bushman waterfalls

III.Is the direction of rotation of a vortex influenced by latitude?

I. Fauna and flora of the waterfalls In the falls, the speed of the stream is

quite high and water is more oxygenated.

A rock fish A carp

A periodontal

Salads koumarou A koumarou

Picture of the tendrils of a plant living in a fall

Is the water of the falls much oxygenated?

Materials: 3 beakers, shaken water, still water, oxygen meter probe.

Experiment:

Observation:In shaken water, the oxygen level is 12.18 mg / L.In still water, the oxygen level is 9.18 mg / L.

The rate of oxygen increased of 75%.Interpretation: When the water is shaken, the oxygen is more

important than when water is still.Conclusion: The flora and fauna of the falls are adapted to a

very high rate of oxygen.

II. Two persons missing at the Old Bushman waterfalls

Beyond the falls Voltaire, at approximately 8,5 km upstream, an unsecured path gives access to other falls after several hours walking (about 4h), called the “Vieux Broussard“, the Old Bushman.

Geographical situation of the falls

Two persons missing at the Old Bushman waterfalls

An accident happened on Thursday, November 2, 2006 to a group of hikers. Twins of 27 years drown in a vortex.

Diagram of the siphon with the inactive vortex

We did an experiment to see how the accident happened• Materials:

Cutting water bottle of 5l connected to a pipe; a elastic, whose acts as a human body, having the same density : d=0.9.d = m body / m water where m is the mass volumetric and d is the density.

Experiment :

Observation : a vortex is created and carries the elastic away in the pipe. The elastic gets stuck in the pipe.

Interpretation : the two men were carried in the vortex. They were stuck in the siphon and died asphyxiated.

Conclusion : a vortex (also called whirlpool) can be very dangerous for humans.

Operating diagram of the siphon

III. Is the direction of rotation of a vortex influenced by latitude?

Cyclone in the Southern Hemisphere

Cyclone in the Northern Hemisphere

To calculate Coriolis acceleration, a, we use the following formula :

With : w : angular speed of sidereal rotation of the Earth. Let us take : j : the number of seconds in a day.Let us take j ~86164 s.v = velocity of the water in motion. Let us take : v=1

m/s.

φ=latitude of the place considered. Let us take : φ~480

Numerical application: Either 100 000 times less than the acceleration due

to gravity (g = 9.81 m / s).So the sink empties until the deviation due to the

Coriolis force was done.

rad/s 2

j

m/s 0,0001 86164

)48sin(4

)][sin(2 va

Lexicon

Siphon: natural conduit swampedA vortex: a circular or helical

movement of the water in a streamThe Coriolis force: it is the centrifugal

force due to Earth's rotation. It is a fictitious force because it exists only because the observer is in a rotating frame so that no force is exerted for an observer in an inertial frame. It exerted on all objects in motion, including the atmosphere and oceans.