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Coriolis Effect

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A rotating Round Earth model predicts that bodies which move through the air will be appear to be deflected Eastwards or Westwards[1] in their path of movement due to the rotation of the earth. This effect has been termed the Coriolis Effect.

The Coriolis Effect, however, appears to be a fictitious effect that is not, and has never been, properly demonstrated with experimental evidence. Its proponents are unable to show that this effect has ever been detected or that it is truly necessary to account for in various operations. The evidence for this effect appears to be based entirely on 'common knowledge', on how things 'should be', and by authors who make 'predictions'; but all articles and documents presented in favor of the "Coriolis Effect" are without reference to, or demonstration of, the critical and necessary experimental evidence to directly prove the matter.

Origin of the Coriolis Effect

In an article titled History of the Coriolis Force (Archive) the origin story of the "Coriolis Effect" is described:

  “ The first detailed study on a manifestation of the "Coriolis" force was made by Giovanni Borelli in the 1660s, when he considered the problem of falling bodies on a rotating Earth. In a theoretical analysis, he found that they will undergo a small eastward deflection during their fall. ”


It has been alleged that the Coriolis Effect plays a part in the ballistic trajectory of artillery, and that artillerymen must account for it for accuracy. We are presented with military range tables for accounting for the Coriolis Effect, and so, it is suggested, the Coriolis Effect must be a real effect.

U.S. Army Artillery Coriolis Table Example

We are directed to Table H from the following document:

The Production of Firing Tables for Cannon Artillery (1967) (Archive)

Pg. 103, Table H, Corrections to Range, in Meters, to Compensate for the Rotation of Earth:


When the Coriolis Effect proponents are challenged on the accuracy or validity of this table, those proponents proclaim that if the table were incorrect then artillery and artillerymen would be routinely inaccurate and miss their targets, and how could that be the case?

Artillery Ballistics Not Accurate

From the introduction of the paper provided we read that military artillery, which is purported to require adjustments for the "Coriolis Effect," is indeed, routinely inaccurate. The first round generally misses its target. Only after missing a number of times, and then adjusting the alignment of the cannon to compensate, does the artilleryman hit his or her target.

From the above 1967 artillery paper (Archive), the same document which was provided to us, we read in the introduction on p.10:

  “ Ideally, a firing table enables the artilleryman to solve his fire problem and to hit the target with the first round fired. In the present state of the art, this goal is seldom achieved, except coincidentally. The use of one or more forward observers, in conjunction with the use of a firing table, enables the artilleryman to adjust his fire and hit the target with the third or fourth round fired. ”

In another artillery paper from 1973, we read a similar quote: (Archive)

  “ When today's field artillery firing tables are used with today's approved delivery techniques [as described in VM 6-401], accurate fire can be brought to bear on targets.

Such a statement can only be made because today's approved delivery techniques recognize that many errors (both precision and bias errors) exist and those techniques arc designed to minimize these errors. The techniques are not designed to produce first round hits, nor does the statement above infer that such hits can be achieved. ”

In 2016 a claimed expert named Guy Schuchman says that, despite GPS and modern improvements, the same problems exist today (Archive):

  “ It's extremely rare for the first round to hit the target. It's just too much data which not all of it can be measured in 100% accuracy and human errors are quite common: small offsets in calculating the coordinates of the target or the gun, small errors in calibration, humidity of the explosive propellant, etc.. The first round is just a test round. When it falls near the target it's the artillery observer's job to see how far and in what offset did it hit away from the target and provide the FDC with the data. ”

A 2017 paper by Australia's Armament Research Service admits the same: (Archive)

  “ Even though great effort is made to calculate the effect of environmental and ballistic variables, an unguided artillery projectile will not reliably strike the exact point at which it is aimed. Although artillerymen strive for first round accuracy, this will still be measured in tens of meters, and in deliberate targeting or combat engagements this introduces a degree of uncertainty when assessing the safety of friendly forces and non-combatants. Properly employed, artillery gun and mortar projectiles and rockets land in a predictable area (accuracy) in a non-predictable fashion (precision), and in common with small arms fire (especially machine guns), the employment of artillery systems yields a ‘beaten zone’ or field of fire into which rounds will fall. This zone is generally cigar-shaped with the long axis falling along the line from the gun to the target, as deviation tends to occur in range rather than azimuth. The length and breadth of the zone is range dependent, as with greater range, external factors have more time to exert influence on the projectile flight. ”

Sharp Shooting

It has been alleged that the Coriolis Effect also plays a part in accurate sharp shooting over long distances. However, we find online references (14:30) where claimed sniper veterans have stated that they have never taken the Coriolis Effect into account when shooting. We point to the U.S. Marine Corps, U.S. Army, and U.S. Navy SEAL sniping manuals, which do not mention the Coriolis Effect anywhere in their sniping texts at all.

Sniping Manuals

U.S. Marine Corps Sniping Manuals
1981 FMFM 1-3B Sniping (Archive)
2016 MCTP 3-01E Sniping

U.S. Army Sniper Field Training Manuals
1994 FM 23-10 Sniper Training (Archive)
1989 TC 23-14 Sniper Training and Employment
2003 FM 3-05.222 Special Forces Sniper Training and Employment (Archive)

U.S. Navy SEAL Sniping Manual
US Navy SEAL Basic Sniper Training
US Navy SEAL Sniper Training Program

The sniper must know the general principles of: perspective, vanishing point, perspective drawing, delineation, and geographical areas of intelligence operations. However, the words "Coriolis" or "Coriolis Effect," do not appear anywhere in the U.S. Marine Corps, U.S. Army, or U.S. Navy SEAL sniper manuals.

Coriolis Not Found.png

The reader might ponder why the U.S. Military does not teach this allegedly important effect to its snipers.

Misleading References

The internet is rife with references that the accounting of the Coriolis Effect is actively used, but this is an assumption without demonstration.

The World’s Longest Sniper Kill: The Enemy Shot Dead at 3,871 Yards (Over 2 Miles Away) (Archive)

  “ To understand the complexity of the shot, it’s best to start with a sniper maxim: sniping is weaponized math. Although a .50 caliber sniper rifle bullet can fly as far as five miles, a host of factors including gravity, wind speed and direction, altitude, barometric pressure, humidity and even the Coriolis Effect act upon the bullet as it travels. Even worse, these effects increase the farther the bullet travels. A successful sniper team operating at extreme distances must do its best to predict exactly how these factors will affect the bullet and calculate how to get the bullet back onto target. ”

This quote actually says "these are the factors that will affect the bullet," rather than "these are the factors that the sniper accounted for." One is a commentary by the author and the other is a depiction of process. The reader should be able to see and understand that there is a difference.

Deflection of Falling Bodies

From the 17th century well into the 19th century the deflection of falling objects was a hotly debated subject, and numerous experiments were conducted to study the landing path of bodies when dropped from high distances. To protect from the wind and elements the experiments were conducted within towers, high churches, and down underground mines and shafts.

From the History of the Coriolis Force (Archive) piece by the Geophysical and Industrial Flows Laboratory there is only one experiment which author of the article references in favor of the Coriolis Effect. All other papers referenced in the article appear to be theoretical analysis'.

  “ Only at the beginning of the 19th century were experiments done in a sufficiently careful manner to detect the deflection. For example,

J.F. Benzenberg (1804): Versuche über das Gesetz des Falls, über den Widerstand der Luft und über die Umdrehung der Erde nebst der Geschichte aller früheren Versuche von Galiläi bis auf Guglielmini, Mallinckbodt, Dortmund. ”

This is one of the Deflection of Falling Body Experiments. From 'The Report of the Sixteenth Meeting of the British Association of the Advancement of Science' (Archive) we find an analysis of Dr. Benzenberg's experiments:

  “ In the beginning of this century, Dr. Benzenberg undertook new experiments at Hamburg, from a height of about 240 feet, which gave a deviation of 3·99 French lines; but they gave a still greater deviation to the south. Though the experiments here quoted seem to be satisfactory in point of the eastern deviation, I cannot consider them to be so in truth; for it is but right to state that these experiments have considerable discrepancies among themselves, and that their mean, therefore, cannot be of great value. In some other experiments made afterwards in a deep pit, Dr. Benzenberg obtained only the eastern deviation, but they seem not to deserve more confidence. Greater faith is to be placed in the experiments of Professor Reich, in a pit of 540 feet, at Freiberg. Here the easterly deviation was also found in good agreement with the calculated result; but a considerable southern deviation was observed. The numbers obtained were the means of experiments which differed much among themselves. After all this, there can be no doubt that our knowledge on this subject is imperfect, and that new experiments are to be desired. ”

Setting Aside All Authority

Setting Aside All Authority: Giovanni Battista Riccioli and the Science against Copernicus in the Age of Galileo
by Prof. Christopher M. Graney

Starting with Benzenberg's experiments at the bottom of p.106 (Archive) we read an overview of the saga:

  “ In 1802, Johann F. (1777-1846) also attempted the experiment, in Hamburg, Germany, by dropping balls from a height of 235 feet. Benzenberg recorded an eastward deflection in agreement with theory. He also recorded a smaller southward deflection of 2.4 millimeters, which vanished in a later experiment. Moreover, the extreme values of his measurements varied by as much as nine times their average value, and he detected significant changes in his plumb line caused by the appearance of the sun from behind clouds. Rigge concluded that Benzenberg's results also could not be considered even a qualitive detection of the Earth's rotation.26

Three decades later, in 1831, Ferdinand Reich (1799–1882) took up the experiment, dropping balls down a mine shaft 520 feet deep near Freiberg, Germany. The theoretical eastward deflection was over an inch, and Reich's average experimental deflection was almost exactly that. Although Rigge and others cite Reich's work as an example of a successful detection, his contemporaries noted that his results varied significantly. Still later, experiments in the 1840s in Cornwall with a 1300-foot drop produced wild results, including southward deflections of 10 to 20 inches, while the theoretical eastward deflection is less than 5 inches.27

Thus the question of the deflection of falling bodies was still being investigated and discussed at the turn of the twentieth century. During this time Edwin H. Hall (1855–1938) dropped nearly one thousand balls down a tube in his laboratory at Harvard University, seeking to determine exactly how a falling ball behaves, while Florian Cajori (1859–1930) wrote about a falling ball's mysterious southward deflection. Hall, too, noted that "curious things" could occur in these experiments. More prosaic examples of such curious things in Hall's day included magnetic fields deflecting steel or iron plumb lines from the perpendicular, and forces caused by magnetically induced electric currents in conducting metal balls. More extreme examples included plumb lines in a deep mine shaft that were observed not to be parallel, and balls falling down the same mine shaft that were observed never to reach its bottom!28

Today, when turbulence and chaos are familiar concepts in physics, physicists are not surprised that dropping heavy balls from a tower fails to reveal the Earth’s rotation. Nor are they surprised that a ball falling through a great distance deviates unpredictably from its expected path, and that two identically dropped balls do not land in the same place. But even a century ago, the recalcitrant nature of this delicate but apparently straightforward experiment must have appeared to have been “curious” indeed—and all the more so in Riccioli's or Hooke's or Guglielmini's time, when such things as induced magnetic effects were unknown.

This raises an interesting question regarding Riccioli's Coriolis effect argument against the Earth's diurnal rotation. Riccioli supposed that Earth's rotation should reveal itself in an easterly deflection of a heavy falling body. Newton wrote that the "advance of the body from the perpendicular eastward” will be very small, but "enough to determine the matter of fact.” This simple test, which appears to involve nothing more than the initial velocity of the ball, the downward pull of gravity, and the upward drag of air resistance, should discover (as Newton wrote) the Earth's diurnal rotation. Yet it is bedeviled by all sorts of “curious things" seemingly beyond explanation. Absent the sort of Herculean effort made by Guglielmini, Benzenberg, Reich, and Hall—the kind made by scientists who know an effect must exist and are determined to find it—this simple test will fail to detect Earth's motion. ”

Failed Experiments

In the above work Prof. Graney further suggests that efforts were made to hide or otherwise not report failed experiments (Archive):


Earth Not a Globe Chapter

In the book Earth Not a Globe, its author Samuel Rowbotham devotes an entire chapter to the Deflection of Falling Bodies experiment saga.

Deflection of Falling Bodies
by Samuel Rowbotham (Archive)

In this chapter Rowbotham walks us through numerous experiments, the inconsistencies among them, and concludes his chapter with:

  “ Thus it is admitted that deflection from a height of 300 feet "is so small as to be practically inappreciable;" that "great heights are necessary for giving only a deviation of one-tenth part of an inch;" that when this amount was observed, "at the same time deviation to the south was given, which was not in accordance with the mathematical calculations;" that "the experiments have considerable discrepancies among themselves;" that "the experiments differed very much;" that "after all there can be no doubt that our knowledge on this subject is imperfect;" that on repeating the experiments with the utmost possible care down a shaft of 1320 feet in depth, the bullets did not fall easterly at all from the plummets, "but from 10 to 20 inches south of the plumb-line," and out of forty-eight bullets, forty-four fell "on the south side of the shaft, in situations which precluded exact measurements of the distances being taken;" and, finally, that puzzled mathematicians, with their ever ready ingenuity to make facts agree with the wildest of theories, even with those of a opposite character, conclude that "falling bodies may have either north, south, east, or west deflection from the plumb-line." What value can such uncertain and conflicting evidence possess in the minds of reasoning men? They are shameless logicians, indeed, who contend that, from such results, the earth is proved to have a diurnal rotation! ”

Schlebusch Drop Plot

On p.271 of Weather Vol. 58 (Archive), we find an example of the results of such drop experiment that encouraged speculations of the Coriolis Effect:

  “ In 1803 an experiment, dropping iron pebbles in a 90m deep mine shaft, was conducted in Schlebusch, Germany. The event attracted the interest of the scientific community, and the 24-year old German mathematician Carl Friedrich Gauss and the 53-year old French mathematician Pierre Simon de Laplace volunteered to calculate the theoretically expected deflection Fig.5 ”

Schlebusch Experiment Plot.png

One quickly sees that the results are not consistent and that any argument in favor of the Coriolis Effect would need to be made on basis of statistics in these types of tests.

If the "Coriolis Effect" shifted the pebbles to the East by about 12 units, then how would this explain the Eastwards concentration of pebbles between 20 and 30 units? If we take away the Eastwards deflection of the "Coriolis Effect" from that group we find that those pebbles are still biased to the East. One would have to know why they are biased in order to know whether the Coriolis Effect had anything to do with it or not. The fact that they were already predisposed to Eastwards bias casts doubt on the matter.

As Rowbotham and others relate, other experiments did not show this Eastwards bias. Picking any few tests as evidence of the Coriolis Effect would be fallacious. Unlike other science cornerstone experiments, which have been repeated by classrooms, laboratories, and research groups for hundreds of years, these experiments were dropped from classroom and scientific interest.

Torsion Balance Experiments

Very sensitive Torsion Balance experiments began in 1889, with Barron Rosland von Eötvös' attempt to detect the Coriolis force.

Foundations of Modern Cosmology
by Professor John F. Hawley (bio), and Katherine A. Holcomb

From p.219 of the above text (Archive) we read:

  “ The first highly accurate experiment to test the equivalence principle was performed in 1889 by Barron Rosland von Eötvös. Eötvös constructed a device called a torsion balance. He suspended two bodies of nearly equal mass but different composition, from a beam which hung from a very fine wire precisely at its center. If the magnitudes of the Coriolis force (from the Earth's rotation) and the gravitational force had differed between the bodies due to their differing composition, Eötvös would have been able to detect a twisting of the wire. None was seen, and Eötvös was able to conclude that inertial and gravitational mass was equal, to approximately one part in 10^9. In the 20th century, Robert Dicke and others pushed the limit of such an experiment to 10^11, but the Baron's results were sufficient to convince many, including Einstein, that inertial mass and gravitational mass are equivalent. ”

Later experiments of the same torsion balance design produced similar results. No effects from any external forces or sources could be found. See Variations in Gravity.

Water Currents

Laboratory Water Vortex Experiments

In the 1960s a researcher named Ascher Shapiro claimed that water vortex direction was due to the "Coriolis Effect". The experiments started with bathtubs and then escalated to six foot wide tanks of water: (Archive)

Shapiro’s Bathtub Experiment
by Conor Myhrvold
November 1, 2011

  “ Over forty years ago, in the 1960s, the world briefly became captivated with how a bathtub drains. Did something called the Coriolis effect influence the twirling water?

The Earth’s rotation influences how fluids swirl on the planet’s surface. It’s why low-pressure systems in the northern hemisphere twist counterclockwise. This phenomenon, known as the Coriolis effect, is the appearance of an object to deflect to one side in a rotating reference frame. Since it is such a tiny effect on small scales, no one had yet proven that this inertial force actually affects how water leaves a bathtub, despite many previous efforts.

In 1962, the same year that Watson and Crick received their Nobel Prize for the discovery of the double helix, MIT professor Ascher Shapiro, an expert in fluid mechanics, set up an elaborate test to try to change that. Shapiro’s elementary experiment, which started with a bathtub, quickly turned into a complicated and ambitious undertaking that involved a tank six feet wide and six inches deep.

The Coriolis effect at MIT’s latitude, 42°, was just “thirty-millionths that of gravity, which is so small that it will be overcome by filling and even temperature differences and water impurities,” reported one of many newspapers and periodicals that covered the results of Shapiro’s experiment. After much tinkering to cancel out these interferences, and presumably a hefty water bill, Shapiro found the answer: the Coriolis effect does indeed cause a bathtub vortex in the northern hemisphere to swirl counterclockwise.

But even after his results were published in a letter to Nature, Shapiro’s confirmation drew the skepticism of readers. In correspondence with one reader, Shapiro noted: “Many results contradictory to this have been reported in the literature but all of them have involved faulty experiments due to a lack of realization of how sensitive the experiment is.” He was supported, however, by colleagues in the Northern hemisphere who confirmed the counterclockwise bathtub drainage, while those in the Southern hemisphere demonstrated the same effect in the opposite direction—a clockwise flow—just as anticipated.

In a world without electronic communication, where author correspondence was a more prolonged affair, a sort of chivalry existed between a scientist and a popular audience who took an interest in academics. Scrawled with a pencil on back-and-forth correspondences between Shapiro and his fans and housed today within a dusty and faded folder in the MIT archives are the records of reprints being sent, of questions being answered, and of careful and nuanced responses that understated Shapiro’s high standing at MIT. A Ford Professor at the time, and later elevated to Institute professor, Shapiro took time to send article reprints for those who asked for it and to answer mail from inquisitive readers, some of whom promoted dubious questions and claims.

...Who would have thought the swirl of a bathtub would have been a matter of great interest? For a seemingly insignificant problem, the bathtub controversy loomed large in Shapiro’s career until his death in 2004. The first line of his obituary in the Boston Globe read: “Dr. Ascher Shapiro wanted to get a handle on how fluids move whether they were swirling down the bathtub drain, or flowing through the human body.” ”

Controversy because other researchers were getting different and inconsistent results. Shapiro claimed that he could perform the experiment and that all other researchers were wrong.

The below shows that even with extreme care the direction of the vortex can be influenced by very small perturbations such as how the lid is lifted. (Archive)

  “ At Tom Fink’s invitation, Professor Lloyd M. Trefethen of Tufts University, USA, spent a short sabbatical in Mechanical Engineering in 1964/65. Already famous for his work on surface tension phenomena, he led us into a repeat of the experiments on the bathtub vortex that had recently been conducted by Ascher Shapiro at MIT. After much careful design, a circular tank of some 2.4m in diameter and 0.4m depth was constructed and installed in one of the subterranean dungeons of the old Peter Nicol Russell building. Carefully designed procedures and their diligent execution resulted in absolutely conclusive results that were published in Nature (Trefethen, et al, 1965). A re-enactment for the local media was a disaster: Bilger and Tanner muffed the removal of the covering baffles creating a great vortex in the water that then went out the wrong way. ‘Scientists baffled’ cried the media. We even made Time magazine! ”

When the lid was removed the 'right' way a 'correct' direction occured and when the lid was removed in a 'wrong' way an 'incorrect' direction occured.

In Flow, Nature's Patterns, a Tapestry in Three Parts (Archive) by Dr. Phillip Ball (Bio) the author gives an overview on p. 47:

  “ A popular notion says that the rotation of the earth starts the bathtub vortex spinning. But while it is certainly true that this rotation controls the direction of the giant atmospheric vortices of cyclones, which rotate counter-clockwise in the Northern Hemisphere and clockwise in the Southern, the influence of the Earth’s rotation on a micro-cyclone in the bath should be extremely weak. Biesel claimed that it cannot be responsible for the bathtub vortex because, contrary to popular belief, they may rotate in either direction at any place on the planet. But is that really so? In 1962 the American engineer Ascher Shapiro at the Massachusetts Institute of Technology claimed that he had consistently produced counter-clockwise vortices in his lab by first allowing the water to settle for 24 hours, dissipating any residual rotational motion, before pulling the plug. The claim sparked controversy: later researchers said that the experiment was extremely sensitive to the precise conditions in which it was conducted. The dispute has never quite been resolved. We do know, however, why a small initial rotation of the liquid develops into a robust vortex. This is due to the movement of the water as it converges on the outlet. In theory this convergence can be completely symmetrical: water moves inwards to the plughole from all directions. But the slightest departure from that symmetrical situation, which could happen at random, may be amplified because of the way fluidflow operates. ”

An abstract ([Archive]) at the Physical Society of Japan states:

  “ It has long been controversial whether the Coriolis force due to the rotation of the earth plays a significant role in the generation of the bathtub vortex in small vessels such as bathtubs. ”

Shape of the Drain

Many sources maintain that the shape of the container and the drain plays more of a role in the direction of the water than the alleged 'Coriolis Effect'.

Sorry, Wrong Answer: Trivia Questions That Even Know-It-Alls Get Wrong (Archive)
by Rod L. Evans Ph.D.

  “ Some misconceptions are so common that they are embraced by even cartoon characters. For example, in a particularly popular episode of The Simpsons, "Bart. vs Australia," Lisa tells Bart that toilets in the Northern Hemisphere (including America) drain counterclockwise, whereas those in the Southern Hemisphere drain clockwise. Lisa's confusion stems from misunderstanding the Coriolis Effect, the inertial force that deflects objects moving above the Earth--rightward in the Northern Hemisphere and leftward in the Southern Hemisphere (including Australia). Bart Simpson doesn't accept Lisa's conclusions, calls up Australians to find the truth about their toilers, and manages to create a diplomatic incident. Factually it was Lisa, however, who was mistaken. Australian toilets flush in the same direction as toilets in the Northern Hemisphere. Although the Coriolis Effect can and does influence large bodies of water and air masses in the atmosphere, its influence on the direction of tiny quantities of water in a sink or a toilet bowl is negligible compared to the effect of the shape of receptacles and the direction of flow from which they were filled. ” - Earth Science: Semester 1 (Archive)

  “ water draining in sinks, tubs, or toilets DOES NOT rotate according to the Coriolis effect. The water drains based only on how the water is poured or the shape of the drain ” (Archive)

  “ Many people think the Coriolis effect makes water in baths and sinks drain in different ways - anti-clockwise in the Northern hemisphere and clockwise in the Southern hemisphere. However, baths and sinks are too small to be affected and the direction that the water drains is more likely to be caused by the shape of the sink or the bath, the slope of the floor and the shape of the drain. ”

A Student's Guide to Earth Science (Archive)

  “ The direction that water spins as it goes down the drain is due to the shape of the bathtub or sink--not to the Coriolis effect. ”

Thomas Humphrey, a senior scientist at the San Francisco Exploratorium, says (Archive):

  “ It is impossible to find a cup full of water that does not have some average net motion; it will always be going one way or the other, and that little amount of angular motion is enough to swamp the Coriolis effect. The net motion in the water becomes much more pronounced as the water is forced to move in toward the center of evacuation, causing the normally invisible flows in the water to become visible as the water nears the drain. The ultimate direction of that flow is random--it can go one way one time, the other way the next. ”

Veritasium and Smarter Every Day Experiment

A popular video Does Water Swirl the Other Way in the Southern Hemisphere? claims to demonstrate the rotation of the earth with a drain experiment. A kiddie pool was drained, concluding that the result was due to the rotation of the earth.

Meteorologist Tom Di Liberto at American Scientist goes over the history of the water swirl controversy and explains that this video is not sufficient proof of the earth's rotation: (Archive)

  “ All things being equal, if you make sure that the water is motionless and no other forces are introduced during the process, Coriolis would be the big winner in the battle royal of forces acting on the liquid draining from that kiddie pool. And for Muller and Sandlin, it worked! They tried their experiment three times in each hemisphere. In each case the water rotated clockwise in the southern hemisphere and counterclockwise in the northern hemisphere. Proof! Right?

Well, not so fast. The YouTube experiments were actually based on previous ones done in a laboratory setting. In those highly controlled settings, scientists at MIT in the 1960s were able to show that Coriolis could work on a draining tub. In fact, I have been told that graduate students at MIT still do this experiment today in one of their classes. The major difference between the past examples and the current YouTube version is that one was done in a lab with a fine control over outside forces and the other uses a kiddie pool set up on a plywood platform in a garage or sheltered patio. In the video experiments any number of things may have introduced an outside force that could swamp the comparatively tiny influence from the Earth’s rotation. Temperature differences in the water could create currents; tiny bumps in the texture of the kiddie pool or plywood could guide the flow; the way the valve released the water could steer the movement; and, especially for the outdoor experiment, a slight breeze could push the water along. A systematic error could have led to the same consistent results seen in the videos.

This is not to say these YouTube experiments did not work. It’s just that a lot of other things could have affected the results besides the Earth’s rotation. Of course, regular folks do not have access to the type of laboratories and equipment needed to control for all other factors and allow the Earth’s rotation to determine the outcome. And part of the purpose of these videos is to show viewers an experiment they can recreate on their own.

Maintaining that degree of accessibility while satisfying skeptics like me would involve putting together a larger sample size of experiments similar to the ones made by Muller and Sandlin, done in different locations across both hemispheres. Then we could get a better idea of whether the setup shown in “The Truth about Toilet Swirl” did in fact allow the Coriolis effect to shine. Until then, I’ll remain unconvinced that what we saw truly resulted from the Coriolis effect.

Ultimately, of course, this is nitpicking. The videos were educational, and the explanation of what the Coriolis effect means for air or water moving on Earth was on the money, regardless of whether I completely accept the experiment’s setup.

Therefore, I guess the only thing left to do is to assemble an army of kiddie-pool Coriolis experimenters to figure this out once and for all. If you bring the pool, I’ll supply the water (void in California). The Earth will provide the spin. ”

D. S. Parasnis

Professor Parasnis of the University of Lulea, author of Principles of Applied Geophysics, wrote to New Scientist to inform them of the following: (Archive)

Letters: In a spin
  “ It is indeed surprising that the myth of a discernible Coriolis force effect on the water in a bath tub persists. Apart from the weakness of the force pointed out in the editorial, the myth was experimentally examined in 1965 by L. M. Trefethen et al in an extremely careful experiment and found to have no basis (‘The bath-tub vortex in the southern hemisphere’, Nature, vol 207, p 1085). ”
D. S. Parasnis University of Lulea, Sweden

Large Scale Water Currents

We find the assertion that large scale water currents rotate in accordance with the "Coriolis Effect" to be untrue. See Coriolis Effect (Weather)

Wind Currents

We find the assertion that the wind currents generally rotate in accordance with the "Coriolis Effect" to be untrue. See Coriolis Effect (Weather)


Many of these discussions are often put to an end after a simple request of evidence. 'Mountains' of evidence are claimed to exist for phenomena such as this, yet when the Round Earth proponent is questioned in a simple and polite manner on the necessary demonstration, we find that the response is generally, to any reasonable standard, woefully insufficient. Data should surely exist in which an experiment is repeated again and again by science investigators with the same result, rather than sparse references to singular instances in which a correct rotation or event occurred. It is quite curious that this effect cannot be clearly demonstrated, and is so easily defeated with such simple questioning, despite our opponent's access to the vast collection of human knowledge that is the internet.

See Also

Flat Earth Topics on Rotation and Revolution

  • Michelson-Morley Experiment - Light velocity experiment which suggests a lack of Earth's motion around the Sun
  • Sagnac Experiment - Experiments which show that light's velocity is indeed affected by detector motion
  • Airy's Failure - An experiment which suggests that the stars are in motion, rather than the Earth
  • Time Dilation by Latitude - The predicted time dilation caused by Earth's rotation does not occur
  • Aviation - Mechanical air flight assumes a flat, non-rotating Earth

Round Earth Topics on Rotation