Scroll down to read this post.

 

Please consider supporting my work here at Behind the Black. I keep the website clean from pop-ups and annoying demands. Instead, I depend entirely on my readers to support me. Though this means I am sacrificing some income, it also means that I remain entirely independent from outside pressure. By depending solely on donations and subscriptions from my readers, no one can threaten me with censorship. You don't like what I write, you can simply go elsewhere.

 

You can support me either by giving a one-time contribution or a regular subscription. There are five ways of doing so:

 

1. Zelle: This is the only internet method that charges no fees. All you have to do is use the Zelle link at your internet bank and give my name and email address (zimmerman at nasw dot org). What you donate is what I get.

 

2. Patreon: Go to my website there and pick one of five monthly subscription amounts, or by making a one-time donation.
 

3. A Paypal Donation:

4. A Paypal subscription:


5. Donate by check, payable to Robert Zimmerman and mailed to
 
Behind The Black
c/o Robert Zimmerman
P.O.Box 1262
Cortaro, AZ 85652

 

You can also support me by buying one of my books, as noted in the boxes interspersed throughout the webpage or shown in the menu above. And if you buy the books through the ebookit links, I get a larger cut and I get it sooner.


Ecuador At The Equator: Coriolis Effect demonstration

An evening pause: I think this video, taken at the equator in Ecuador, nicely proves the Coriolis Effect. In fact, it is remarkable how short a distance you need to travel on Earth to flip the effect.

Genesis cover

On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.

 
The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.


The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.
 

"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News

31 comments

  • Edward

    At the risk of spoiling the fun:
    I spotted the trick right away. Did anyone else notice?

  • Phill O

    Absolute hogwash!

    If you notice in the north video, there is already some circulation in the direction they want for proof.

    Only extremely large scale patterns can be affected by the Coriolis effect: like cyclones, hurricanes and typhoons (all the same). Dust devils and tornadoes are of to small a scale to be affected and rotate in either direction in each hemisphere.
    Over large distances of hurricanes, there is an appreciable difference in velocity of the earth’s surface at the north and south boundaries and the Coriolis effect is observed.

    Now, it is common in long distance shooting to consider the Coriolis effect, and this also is hogwash even for distances of even 2 miles.

    The physics is as follows:
    A bullet shot due north has a north velocity vector and an East velocity vector. People have not considered this east vector. It is of the same magnitude as the east velocity vector of the target. Yes, your target has moved. We will say 10″. The east velocity vector of the bullet has also displaced the bullet by 10″ east

  • Phill O

    Edward, you posted as I was writing.

    Phill

  • mpthompson

    I think hogwash is the polite term. The effect from which side of the basin she pours the water into has a million times the impact of any Coriolis forces.

    That being said, is it true that train tracks running long straight north-south distances have wear patterns due to a Coriolis effect on the moving train?

  • Phill O

    In Wyoming, the wear will be on the east track as in Montana and the Lethbridge Alberta area. This would be due to the wind affect. IMO

  • Edward

    mpthompson asked: “That being said, is it true that train tracks running long straight north-south distances have wear patterns due to a Coriolis effect on the moving train?” \

    The side to side motion of the train due to the not-quite straightness of the tracks (and the wind, as Phill O noted) has much more effect than the Coriolis effect. The speed change on an object with the rotational speed of the Earth is very small at the speeds that we travel. Phill O’s bullet and artillery shells see more Coriolis effect, as they travel northward (or southward) much faster and can end up inches (or feet/meters, for artillery) off target.

    A passenger train travelling about 80 mph is travelling about 120 ft per second. Even at 60 degrees north latitude, the westward acceleration of the train is about 0.02 feet per second per second of travel. Yes, that comes out to about 0.001 G of acceleration. Or rather, deceleration, as the train is slowing down relative to the Earth’s spin axis. Smooth as a train may be, it has more sideways motion than that tiny amount of Coriolis acceleration.

    Although it does not travel at the same speed as the train or bullet examples, the next time you are in a museum or science center with a pendulum, notice how slowly it rotates. The Coriolis effect is the driver of the precession.

  • Max

    Nice comments all of you, very educated. Not at all as you would expect if the question was asked of “the man on the street”. Could you just imagine the answers?
    All I could add, as is my habit to put things in layman terms or examples, is that the Coriolis force affect on the pendulum mentioned is to move that pendulum 360° with one revolution of the planet. In other words 1/2 as fast as the second hand on the clock.

  • Okay, I am not a scientist or an engineer, but I am unconvinced that this was entirely hogwash. It is clear that the woman carefully fills the sink from opposite sides between north and south, producing a small circular rotation in the desired and opposite directions, but the circular rotation accelerates considerably in each direction once the water starts draining.

    I just tried this in a sink. Though I could cause a rotation as water drains in both a clockwise and counterclockwise direction by circulating the water appropriately prior to opening the drain, in the counterclockwise direction that circulation dissipated while in the clockwise direction it remained strong.

    I would like an explanation that will clarify this for me. As far as I can tell, this is not entirely a magic trick, and does demonstrate the difference between north and south.

  • Jerry greenwood

    Wikipedia has a decent explanation way down in the article along with a description of an experiment carried out in Boston that makes the answer rather ambiguous.

  • Andrew_W

    Mr Zimmerman, when an ice skater pulls their arms in their rate of spin increases. water is being drawn towards the center of rotation.

    Try the experiment at home, get the water moving SLOWLY clockwise before you pull the plug, then do it again with the water moving slowly counter-clockwise. The first time she did it, on the equator, she’d let the water stand for a long time before pulling the plug, ensuring there was no water movement.

  • Andrew_W

    Mr Zimmerman, sorry, I didn’t read your whole comment. My bad.
    “in the counterclockwise direction that circulation dissipated while in the clockwise direction it remained strong.” That’s funny, If anything the counter clockwise rotation seemed weaker for me too, maybe you’re onto something. Are you right handed? Maybe it works differently for a left handed person?

  • Phill O

    Momentum is conserved. As with the ice skater example, neutron stars rotate much faster after the formation than before. One way to stabilize a satellite (in rotational terms) is to have two pieces ejected while in orbit and the angular momentum goes with them.

    Rest assured, this video is a trick! Basic physics!

  • wayne

    (I honestly only skimmed everyone’s comments before I jumped the gun and hit submit, but I know the answer to this! And excuse if already discussed.)

    mpthompson touches exactly upon it, “The effect from which side of the basin she pours the water into has a million times the impact of any Coriolis forces.”
    The key operative phrase being, “a-million-times-the-impact-of-any-Coriolis-force.”

    It is extremely difficult to actually measure a Coriolis effect, even in very tightly controlled, full-scale, laboratory conditions.

    –It’s practically impossible in a non lab setting. And as others have mentioned– it’s far easier to extraneously manipulate (knowingly or not) the effect, and even with very tight controls, the error bars are pretty big.

    –It has been done and it is as an actual effect, but using your sink drain doesn’t qualify as “demonstrating the effect.”

    In the lab– they have to let the water sit for a (relatively, incredibly) long time cuz’ water is never really “at rest,” and they have to control for ground motion, passing trains/trucks/cars, people walking on the 2nd floor, mechanically induced vibrations from motors, etc., etc., etc.) And even the motion of ‘pulling the plug,’ to let it drain, perturbs the water far greater than the actual effect.
    >Think of the controls they use to stabilize the LIGO instrument. To replicate the Coriolis effect requires that type of precision. (not the exact magnitude, but a similar order of precision.)

    If I can find the exact link I’m thinking of, I’ll post it later.

    For right now—
    try this:

    Laboratory Demonstrations of Planetary-Style Fluid Dynamics
    https://youtu.be/S0_-uITuxYQ
    29:22

    (and I only had a short time to review this vid as well)

  • Karl Fredrickson

    I saw the same thing when I went to this outdoor museum along the equator in Ecuador. They actually do a series of quite convincing demonstrations, one involving an egg. I was most excited to share this with people back home, only to have a physicist bring me down to earth unrotated. Alas, a perusal of scientific sites on the internet convinced me (including the 1962 Nature article) that it is, indeed, impossible to consistently show such an effect, even at a distance of thousands of kilometers, let alone a few meters! But I am eager to try it on my during my next trip down under.

  • wayne

    Karl-
    Good stuff!

  • wayne

    Mr. Z.,
    I’ll try to locate an appropriate link that covers this in depth. (it might take a while, but I’ll email you if it does, and if I can find what I want.)
    It’s not a ‘trick’ so much, but rather a very subtle manipulation (knowingly or not) of the water.
    Even in a lab setting, “pulling the plug” on the drain has to be very well controlled, the Coriolis effect is so miniscule on that amount of water that any number of extraneous factors overwhelm the actual effect.
    (Hurricanes and Tornado’s are a different matter. We know it’ s an actual effect on large scales, and there’s no rational reason why it wouldn’t work on very small scales, but actually measuring it, therein lies the difficulty.)

  • Matt in AZ

    Veritasium has a pretty good video on coriolis effect draining under very controlled conditions.

    The Truth About Toilet Swirl – Southern Hemisphere
    https://youtu.be/ihv4f7VMeJw

  • wayne

    Matt in AZ-
    Good one.

    This is not exactly what I want to share, but interesting nonetheless:

    Rotating Frames of Reference
    MIT OpenCourseWare 2012
    https://youtu.be/IOcrHOc23N4
    15:17

  • wayne

    chapter 2 Coriolis accelerations
    in the above video, cued to the relevant start.
    https://youtu.be/IOcrHOc23N4?t=519

  • Max

    Z man said;
    “I would like an explanation that will clarify this for me. As far as I can tell, this is not entirely a magic trick, and does demonstrate the difference between north and south.”

    I’m not a scientist either but I will give it a shot.
    The demonstration in the bowl was theater for the tourists. The direction of spin was caused by which side she poured the water. I can influence the direction of a spin in my kitchen sink by misaligning the holes in the strainer with the holes in the drain base. Once a direction of flow is established, gravity and momentum increases the speed of the vortex in the same direction. (It’s funner with a 2 liter pop bottle)
    The Coriolis effect at the equator is not a spin but a roll. Just as a pendulum on the equator will only swing forward and back, but slightly higher on one side than the other. For the same reason that a satellite above the equator moves in one direction. Or better yet, everyone is familiar with the merry-go-round. A ball thrown from one side to someone on the other must be timed correctly. In this case the equator on a merry-go-round would be the equivalent of standing on the outer vertical edge.
    The Coriolis affect is too weak to have a noticeable difference with anything small. Tornadoes will spin in both directions, even on the same supercell. But a low pressure system or a hurricane, hundreds of miles across, will be moving at different speeds on one side than the other causing it to spin. The direction of the spin is determined by which hemisphere. like the merry-go-round, if you were hanging upside down you would throw the ball in the opposite direction that you did when you were on top.
    InterestIng;
    Hurricanes will not cross the equator. None have moved closer than 5° before they begin moving away. Also high pressure move/rotate in the opposite direction of a low pressure…
    Holding a spinning bicycle tire while standing on a barstool will cause the barstool to spin depending on the direction you tilt the bicycle wheel. The fundamentals of how gyroscopes move/position satellites.
    I was about to explain how drivelines spin at different rates on the inside of the angle then the outside, but I think I’ll stop there.

  • Max: I need an explanation for why the rotation in my sink appeared to dissipate as it drained when I created a counter-clockwise rotation, but remained strong in the clockwise direction.

    I admit that my bathroom experiment hardly ranks as a controlled experiment, and that might be the explanation. However, I do think that the effect is not so easily overcome as these videos suggest. When you drain your bathtub, it seems to me that the water always rotates in the same direction.

  • pzatchok

    Its witchcraft.

    I’m going back to the flat earth conference.

  • Andrew_W

    Mr Zimmerman: “but remained strong in the clockwise direction.”
    If that’s down to the Coriolis effect you should be in the Southern Hemisphere.

  • Andrew_W

    When I do the experiment in my sink I use the cold tap which is the right-hand tap, the tap itself creates movement in the sink in the clockwise direction, when I stir it in the counter-clockwise direction I tend to stir near the center of the sink – around the plug. Possibly there are two vortices happening at once; an outer clockwise and an inner counter clockwise, the water starts off going down counterclockwise but then the outer clockwise vortex starts to have an effect and the vortex weakens.

  • Phill O

    I needed to re-examine the bullet trajectory and have the best explanation for my mind.

    The Coriolis effect is based upon differential surface speed. The surface is the earth. At Rodeo NM, we are at about 31degrees latitude. Using the calculator (http://www.easysurf.cc/circle.htm#cetol1) we have a speed of 892.59 mi/hr.

    My buddy shooting at 1 mile has a bullet “hang time” of 3 seconds. The following data give a Coriolis “drift” of 2.3 inches per second of “hang time” or 6.9″ to the east of where he aimed. This data was generated using the difference in surface speed calculated with the above link. The bottom entry is for a cannon shot at 25 miles. We can see that as the distance increases, the Coriolis becomes important. Consider the Howitzer which shoots multiple shots (3 I believe) and hits a target simultaneously with all three by varying the arc. Since there is a significant time differential between shots (reloading time) and the great distance Coriolis is an important factor.

    Yards Miles Differential mi/hr inch/sec
    1000 0.57 0.08 1.4
    1760 1.00 0.13 2.3
    2000 1.14 0.15 2.6
    44000 25.00 3.39 59.7

    Wind estimation for my buddy is a larger factor. The correction for each mi/hr outweighs the Coriolis. Now, he is very good at windage, shooting 2.5-3.5 inch groups at 1000yards in competition with his 50 cal.

    For Bob’s in house experiment, there are other facts which will outweigh any Coriolis, A slight dent in the drain apparatus could have a dramatic affect.

    The difference in latitude in a sink (one side to the other) is greater than six orders of magnitude lass than the 1000yd shot, so the one who proposed a million time difference is correct.

    Now, this will probably not clear things up for you, but it does for me.

  • Edward

    Robert Zimmerman wrote: “When you drain your bathtub, it seems to me that the water always rotates in the same direction.

    This is undoubtedly true for the reason that Phill O said. “A slight dent in the drain apparatus could have a dramatic affect.” If the sink, tub, toilet, children’s pool, or whatever is not installed level, then that can have a similar effect as a dent or uneven surface. Since the imperfection is the same every time the apparatus drains, we should expect the same results most times.

    For the equatorial video, the water starts with enough motion to guarantee the desired result despite any flaws in the tub that is used. The Coriolis effect a few feet north or south of the equator is virtually zero.

    This is another case in which size matters. Even at Tucson, 32 degrees north latitude, the difference in speed of the southern side of a two foot sink is almost the same as the northern side. Phill O shows that at 1000 yards at a similar latitude gives a speed difference of only 1.4 inches per second (I have not checked the math). For a mere two feet, a similar speed difference would be around 0.001 inch per second (1.4 inches per sec X (2 feet/3000 feet)).

    From Matt in AZ’s video, Derick’s 5 foot wide kiddy pool has a better chance of showing the effect (about 0.002 inch/sec), but it could also just be luck that it just barely and almost invisibly swirled in the correct direction (notice that he unplugs the pool in a way that induces extremely little disturbance). A test of his apparatus could be done by taking it down and setting it up multiple times in order to see if there is consistency. As with the hurricane, the center swirl in the pool becomes far more exaggerated than the initial speed of the water, for reasons similar to those Andrew_W described with the ice skater example.

    Max wrote: “the Coriolis force affect on the pendulum mentioned is to move that pendulum 360° with one revolution of the planet.”

    This observation would only be made at the poles, but would not be due to the Coriolis effect. This effect would be countered every time the pendulum passes the pole, so what would be seen is the swing of the pendulum remaining in one direction. Let’s say it swings in line with the Pleiades, so it always swings in line with the Pleiades. There would be no rotation of the pendulum at the equator for a different reason, the Coriolis effect is zero, there.

    Off of these two extremes, the pendulum will rotate over time, with a faster rotation when it is located closer to a pole, but it will take more than a day to make a complete rotation.

    wayne’s video shows some dynamics equations, showing that the math can get difficult depending upon the frame of reference. For the pendulum, the frame of reference is the spinning Earth, which is why we see the constant linear motion of the pendulum at the pole as being a rotation. It is actually we who are rotating. At the equator, the pendulum’s cable rotates with the Earth, but the direction of the ball (bob) remains aligned with the North Star (Polaris).

    A more basic lesson in the Coriolis effect could be seen if we were ever to create a rotating space station, such as seen in the movie 2001: A Space Odyssey. A person, such as the movie’s Dr. Floyd, at arrival to the station at the center hub would be weightless and traveling at no speed relative to the hub. As Dr. Floyd travels down one of the spokes, he necessarily has to speed up to the speed of the ring portion, which is traveling at quite some speed relative to the hub. The Coriolis effect is the acceleration of Dr. Floyd as his distance from the center of rotation increases. The difference in speed in the rotating object (planet or space station) is what is described half way through Matt in AZ’s video. At the ring, centrifugal forces (toward the hub) would cause Dr. Floyd’s path to curve, relative to the hub and the universe, and give him the feeling of gravity.

    In wayne’s video, the curved path of the ball is seen because the ball does not undergo any Coriolis acceleration and travels straight, relative to the universe, but appears curved to the person in the rotating frame of reference. The cause of the clockwise or counterclockwise rotations of hurricanes is due to the air also traveling in a (relatively) straight line as seen by a geostationary satellite (thus ignoring gravity causing it to travel in a path that curves with Earth’s surface as the planet rotates), resisting the Coriolis acceleration that would be needed in order to remain on the same longitudinal line on the Earth. This is also what should be causing the swirl in the kiddy pool.

    For the air, there is little in the way of structure that would force the molecules to conform to a straight ground track, so from an Earth-fixed observer the air appears to curve, an effect similar to the ball. Dr. Floyd, however, has the structure of the space station’s spoke to accelerate him, otherwise he would be traveling at zero speed when he reached the ring, and the collision would end badly for Dr. Floyd.

  • Edward: Thank you for the detailed response. Very much appreciated. The essential point you and Phill have made is that the force itself is so weak that too many other factors prevent it from showing up in these demonstrations.

  • wayne

    Edward–
    yes, great stuff!
    Mr. Z.,
    good summary, of the Point!

  • Max

    Z man;
    The Coriolis force is counter clockwise in the northern hemisphere. ( I just checked the position of the low pressure coming from California to confirm, they’re getting pounded by rain from the pineapple express?)
    Apparently basin manufactures create the spin on purpose so that toilets and sinks are self cleansing. I used the same method, years ago, in my children’s above ground pool which was circular. I would have them push the water in a whirl pool so all of the debris would collect at the center make it easier to remove.
    I remember as a child making the water in the tub drain manually in different directions but it always self corrected eventually to the manufacturers preferred direction. Using the tip of a toy, I could change the whirl direction automatically depending on which way I slanted the toy.

    Everything in nature seems to have a spin to it, from atoms and DNA to giant storm systems… flowing water in streams or pipes, to plasma in exhausts systems or neon lights.

  • Phill O

    Further to my calculations for the shooter, there is an assumption: the surface of the earth is smooth.

    If the target is raised above the shooting level, it’s speed will be increased and, when shooting up hill, the Coriolis may be negated, or even reversed.

  • Edward

    Phill O,
    You noted: “If the target is raised above the shooting level, it’s speed will be increased and, when shooting up hill, the Coriolis may be negated, or even reversed.

    What an excellent point. My professor didn’t note that effect when teaching us that subject (or maybe I missed it, because he mumbled his lectures into the chalkboard — I wish I were making that up). I just looked up an artillery table (range table) and saw that it has corrections for the target being above or below the gun.

    You learn something every day. I can go to bed, now.

    Thinking about it quickly, it seems to me that the upward angle for the Coriolis effect to be negated (shooting toward the north or south pole) is the latitude of the gun, shooting parallel to the Earth’s spin axis.

Readers: the rules for commenting!

 

No registration is required. I welcome all opinions, even those that strongly criticize my commentary.

 

However, name-calling and obscenities will not be tolerated. First time offenders who are new to the site will be warned. Second time offenders or first time offenders who have been here awhile will be suspended for a week. After that, I will ban you. Period.

 

Note also that first time commenters as well as any comment with more than one link will be placed in moderation for my approval. Be patient, I will get to it.

Leave a Reply

Your email address will not be published. Required fields are marked *