There are many myths in the world, and you have done your best to either prove or dispel as many as you can. One myth–the idea that toilets swirl in the opposite direction in Australia–is not so easy for you to test because it is not exactly convenient for you to make a trip to the Southern Hemisphere and find out, and the results you’ve seen on the Internet are inconclusive.
Does water swirl the opposite way in Australia? No, water does not swirl the opposite way in Australia, at least on a residential scale. For common household items such as sinks and toilets, water will swirl in the direction influenced by the design of the basin.
As such, water will swirl in both directions in both hemispheres, based on the influence of a particular drainage system’s design. There is a larger principle of physics, known as the Coriolis effect, that will influence the direction water swirls for larger atmospheric events, such as hurricanes, but that has minimal effect on normal water drainage.
Which Way Does Water Swirl in Australia?
The idea that water swirls in the opposite direction in Australia and other parts of the Southern Hemisphere is a myth that has been promulgated for many years. Entire episodes of popular television series have centered on this question, and countless YouTubers have gone to work putting it to the test.
It is not necessarily a myth, per se.
On a large scale, for major weather and atmospheric events, it is absolutely proven that water swirls in opposite directions in the Northern and Southern Hemispheres. A hurricane will rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.
The physics behind this is explained through a principle known as the Coriolis effect. (We’ll get into what that is soon.)
Some fun information on these rapidly rotating storms that will be referred to as “hurricanes” in this article: If such a storm occurs in the Atlantic or Northeast Pacific, it is called a hurricane; if it occurs in the Northwest Pacific, it is called a typhoon; and if it occurs in the South Pacific or Indian Ocean, it is called a cyclone.
For simplicity’s sake, we will refer to all such storms as “hurricanes” in this piece, but the characteristics are the same for each, with rapid rotation and low-pressure centers, strong winds, and a spiral arrangement of thunderstorms and heavy rain squalls. When viewed from above, a hurricane looks like an enormous toilet flushing on Earth’s surface.
What is the Coriolis Effect?
The Coriolis effect is an observation of the Coriolis force in action.
The Coriolis force is an inertial or fictitious force that acts on objects that are in motion within a frame of reference that rotates with respect to an inertial frame.
While Newton’s laws of motion describe the movement of objects in an inertial, or non-accelerated, frame of reference, the Coriolis effect describes them in the presence of rotating and centrifugal accelerations, which is necessary due to the fact that Earth is constantly rotating on its axis.
This definition is a little dry and scientific, so let’s try to break down how the Coriolis effect causes water to swirl in opposite directions in the two hemispheres.
Imagine Two Gigantic Pools
Think about two gigantic, circular pools, one in the Northern Hemisphere and one in the Southern Hemisphere.
- Now imagine that one point of each pool is right next to the North Pole and the South Pole, respectively.
- This leaves the opposite point of each gigantic pool sitting significantly closer to the equator.
- These pools are stationary in terms of their location on the Earth, but they are actually making one full, 360° revolution each day as the Earth rotates on its axis.
- During this 360° turn, the point of each pool that is right next to the pole will travel a significantly shorter distance than the point that is closer to the equator, with all of the points inside the pools traveling a comparatively greater distance as they move out from the pole point and a comparatively shorter distance as they move in from the equator point.
- This means that while the whole pool is moving, the point closest to the equator has the most momentum, while the point closest to the pole has less.
- The point closest to the equator is traveling at the greatest velocity, with the velocity of each point within the pool getting less and less until it reaches the point by the pole, which will be close to zero.
Imagine a Drain in the Middle
Now that you can visualize these two gigantic pools as they are rotating in each hemisphere picture them with a drain right in the center, like that in the middle of a circular bathroom sink.
Pulling the plug on the drain will pull the water toward the middle in an attempt to empty your giant pools.
The water that is near the equator point of the pool is traveling too fast, so it gets out ahead of the water closest to the drain, while water closest to the pole point of the pool is traveling too slow, so it lags behind the water closest to the drain.
The water nearest the equator will continually outrun the drain, while water nearest the pole will continually fall behind, creating a swirling effect at the point of entry for the drain.
But Why Opposite Directions?
The thought behind this model makes sense, but why are they swirling in opposite directions? After all, the Earth only rotates on its axis in one direction, right?
Of course, the Earth only spins on its axis in one direction!
However, the pools are swirling in opposite directions due to frame of reference.
If you are at the South Pole facing north, the Earth spinning from left to right will seem like the Earth is spinning from right to left to someone at the North Pole facing south. As such, the water nearest the equator point of each pool will be traveling in opposite directions for the two gigantic pools, creating opposing circular momentum as well.
Therefore, water will give the impression of swirling counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.
Why the Coriolis Effect Doesn’t Matter Much on a Small Scale
If you have read this far, you may be a little confused. How can you say that water does not swirl the opposite way in Australia, yet turn around and claim that the Coriolis effect does cause water to swirl in opposite directions in the different hemispheres?
The reason behind this is that the Coriolis effect is only significantly observable in large examples, like major weather events, such as hurricanes and tropical storms. When considered in small, everyday cases like household drains, the influence of the Coriolis effect is negligible and takes a distant back seat to other sources of angular momentum.
Using the same imaginative process that you used to think of the two gigantic pools near the North and South Poles, imagine your kitchen sink that is full of water.
Your Kitchen Sink and the Coriolis Effect
Yes, one point of your kitchen sink is marginally closer to the North Pole, and the opposite point of your kitchen sink is marginally closer to the equator. This means that when you pull the plug on your drain, the water nearest the equator will outrun the water nearest the North Pole, causing the water to swirl in a specific direction, as defined by physics, while it drains.
However, when the actual distances and rates of momentum are plugged into and calculated using actual physics equations (too in-depth for this article), the results reveal that while there is some Coriolis force present in this small example, it extends out to so many decimal points that it is easier just to round to zero.
It is similar to the concept of how all objects exert a gravitational force. Yes, all objects of mass are constantly pulling on one another. However, this gravitational force pales in comparison to that exerted by the Earth, so instead of sticking to each other, people remain with their feet on the ground.
What Causes Water to Swirl in Household Situations?
Okay, so the Coriolis effect does not influence the direction that water swirls in everyday situations, but you definitely notice the water swirling as it goes down the drain. There has to be some explanation for this, right?
There are, indeed, a number of sources of angular momentum that can influence the direction water swirls when going down your drain. While some of these may seem far-fetched, remember: The Coriolis effect is negligible in everyday situations, so it does not require much force to get your water swirling every which way.
When reviewing these sources of angular momentum, remember that just like they generally override the Coriolis effect, they can also work together or override one another, with the factor or factors causing the greatest net force ultimately determining whether your water is draining clockwise or counterclockwise.
The swirling of toilets is probably the most noticeable place where you observe water swirling in your everyday life. This is due to the mechanics of the toilet and not some larger force determined by geographic location.
When a toilet flushes, water stored in the tank needs to be used to fill the toilet bowl and complete the flush. This pressurized water will be moved from the tank into the toilet bowl, and once the bowl fills and begins to drain, the direction the water swirls as it leaves the bowl will be influenced by the direction the pressurized water enters.
- If the water is moving left to right as it enters the toilet bowl, the toilet will most likely swirl clockwise as it drains
- If the water is moving right to left as it enters the toilet bowl, the toilet will most likely swirl counterclockwise as it drains.
If it seems like the water is not necessarily “jetted” in a specific direction as it fills the bowl, remember that it does not take significant force to get the water swirling in a circular fashion, and once this momentum is built, it will continue swirling along the same path.
Therefore, toilets in both hemispheres can swirl in either direction, based largely on the direction pressurized water fills the toilet bowl.
Threaded Pipe Connections and/or Grooved Pipes
If you are looking at water draining from other sources not influenced by pressurized water, such as bathtubs or sinks, the most likely factor influencing the direction the water swirls is probably due to any threading or grooves in your drainage pipes.
If you have any threaded pipe connections or grooves in your piping system, the water will not follow a completely straight path as it leaves your basin, and as water is pulled from the surface, it will follow the path influenced by the direction your water is moving through the drainage pipes.
This can even extend to any blockages in your piping system. If your pipes are clogged with hair and/or food, the path the water travels as it leaves your residence will be diverted, influencing the direction the water swirls as it enters the pipes.
If your sink or bathtub is not sitting completely level, the direction the water drains will be influenced.
The water on the higher side will have more momentum than that on the lower side, influencing the direction the water swirls as it enters the drain.
Once this pattern of motion is established, the water will continue swirling until the basin is completely empty.
If you have the basin draining and the water running at the same time, such as when rinsing a dish as you are emptying the sink of dirty dishwater, the direction of the water swirl will be influenced.
- If the running water is deflected into the basin from left to right, this will initiate momentum in the basin water and cause it to drain in a clockwise fashion
- Water deflected from right to left will swirl in a counterclockwise fashion.
Human interaction can have an influence on which direction the water swirls down the drain. For example, if you are doing dishes and scrubbing in a clockwise fashion with the plates at least partially in the water, then this increases the likelihood that the water will swirl down the drain clockwise as well if you do not give the water the chance to come to a complete rest.
This can even extend to removing the drain plug. If your pull on the plug is skewed in one direction, this momentum is likely to influence the direction the water swirls down the drain.
While the likelihood of air influencing the direction water swirls down the drain is not overly high, there is a chance it could be a factor if all other forces are negligible, or the breeze is particularly strong.
Even if the breeze is not coming in direct contact with the water, the water’s momentum could be influenced by the following factors:
- A window that is left open when bathing or doing the dishes in the summertime, allowing gusts of a breeze to exert a force on the water
- Portable fans that are running near the water basin
- A heating or air conditioning vent that opens wear a drainage source
Again, while the factors listed in this section exert varying levels of force, they are all greater than the Coriolis force exerted on such small samples and will have a greater net influence on the direction water swirls down a drainage pipe.
Testing the Coriolis Effect in Everyday Life
While we have noted that multiple sources of angular momentum will affect the swirl pattern of draining water in everyday situations far greater than will the Coriolis force, leading to unpredictable swirl directions in both hemispheres, it would be inaccurate to say that the Coriolis force is completely absent.
While the Coriolis effect is not applicable in real-life situations, it can be observed when studied scientifically.
Therefore, in order to see the Coriolis effect in action on a small scale, you simply have to set up an experiment in which all outside sources of angular momentum are completely eliminated.
The following steps can be used to set up an experiment so that you can witness the Coriolis effect in action. Make sure you perform this experiment indoors, or someplace where the breeze will not be a factor:
- Find a large funnel – try to find a funnel that is at least one foot in diameter and has a narrow stem. You will want your funnel to be able to hold a significant amount of water while releasing water slowly, allowing you to view the results of your experiment
- Stopper the funnel – whether you use a piece of clay or fashion some kind of cap, you will need something to hold the water in the funnel. This is a difficult step because you need the stopper to be sturdy enough to hold the water in without being so sturdy that you upset the funnel when trying to remove it. Some funnels come with caps pre-made
- Make a stand – you will need some kind of stand for the funnel so that you will have easy access to get underneath and remove the stopper. There are many ways you can do this, but you need to make sure that the funnel is completely level so that the momentum of the water is not influenced when the stopper is removed
- Fill the funnel with water – once you have your funnel stopped and a level stand in place, fill the funnel with water. Make sure that the water is completely still before you attempt to go any further with the experiment. This can be achieved by placing a small leaf on the water and making sure it does spin or drift before continuing
- Remove the stopper – carefully remove the stopper, making sure that you do not bump the funnel or stand and agitate the water. If you are performing this experiment indoors, make sure that you have an adequate receptacle to catch the water as it drains
- Observe the leaf – as the water drains from the funnel, observe the direction the leaf is spinning. This will let you know the direction the water is swirling as it leaves the funnel. As the experiment is on such a small scale, it will be difficult to observe the direction the water is swirling with your naked eye, so having the leaf as a reference is essential
- Repeat the process – perform this experiment several times. In the absence of any other sources of angular momentum, you should find that the leaf spins in the same direction every time
If this exact same process were used in different hemispheres, the water would swirl in opposite directions based on location. If the same process was used with the equator splitting the funnel in half, the water should theoretically drain straight down, causing no swirl in the leaf whatsoever.
While this experiment is highly sanitized, it does successfully demonstrate the Coriolis effect and how water swirls in opposite directions in the two hemispheres.
What Causes Hurricanes to Swirl the Opposite Way in Australia
Though we have shown that the Coriolis effect in everyday life is not enough to offset other forces of angular momentum in toilets, bathtubs, and sinks, causing the direction of swirling water to vary in household scenarios, hurricanes will always swirl in opposite directions in the different hemispheres. Here is how the Coriolis effect works for these large forces of nature.
The Center of the Hurricane has Lower Pressure
Just like releasing the plug from your bathtub or kitchen sink causes the water pressure to lower in the center of your household basin, the center of a hurricane has a lower pressure than the water and air that surround it.
Higher Pressure Air Rushes In
Just as removing the plug on your sink causes the water to rush toward the drain, the higher pressure air in a hurricane will rush in toward the area of lower pressure.
Similar to our model in which we imagined the large pools in different hemispheres, the water and air nearest the poles will be moving slower with respect to the eye of the storm, while the water and air nearest the equator will be moving at higher speed with respect to the center.
Therefore, the water and air nearest the equator will continually outstrip the water and air nearest the poles as they rush to fill the low-pressure area in the center, causing the hurricane to swirl around the eye of the storm.
The difference is that these forces moving right to left in the Northern Hemisphere will be moving left to right in the Southern Hemisphere, causing hurricanes to swirl counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.
Does Water Swirl the Opposite Way in Australia? Putting it All Together.
The answer to this question is not straightforward. Scientifically, the answer is “yes,” water does swirl the opposite way in Australia. Realistically, though, the answer is “no,” there is no telling which direction water may swirl when being drained.
Because the Earth is constantly spinning on its axis, all objects on its surface are rotating, as well. This creates a phenomenon known as the Coriolis effect that is not explained by Newton’s laws of inertial forces.
As explained by the Coriolis effect, objects nearer the equator are rotating a greater distance than those nearer the poles and, subsequently, with the greater momentum. Therefore, when there is an area of low pressure in a body of water, the water nearest the equator will be moving faster than that near the poles as it approaches the low-pressure area, causing a swirling effect.
For extremely large forces of nature, such as hurricanes, where significant wind speeds and distances are involved, then the Coriolis effect holds true, and when viewed from space, hurricanes in the Northern Hemisphere will look like giant toilets flushing counterclockwise, while cyclones in the Southern Hemisphere will be rotating clockwise.
However, when applied to everyday scenarios such as draining toilets, bathtubs, and kitchen sinks, the Coriolis effect is negligible and has little effect on the direction water swirls when drained.
While the Coriolis effect can be proven scientifically when the proper controls are put in place, there is really no way you could notice it in everyday situations. Other forces of angular momentum will trump the Coriolis effect in household scenarios, with the following factors much more likely to influence swirling water than the Coriolis effect:
- Toilet design
- Drainage pipe structure
- Basin imbalances
- The presence of flowing water
- Human interaction
As such, there is really no way to predict which way water will swirl in Australia when compared to that in the United States, with the influence of local forces and design structures ultimately determining how the water swirls as it is drained.
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