The Coriolis Effect Explained
Does Air Spin in Opposite Directions in Different Hemispheres? Does Water Go Down the Drain in Different Directions in Different Hemispheres?
The Coriolis Effect causes air to spin different directions in each Hemisphere. This can only affect large systems like wind and ocean currents. The effect is too weak to affect minor systems like the direction a toilet flushes.
Due to the Coriolis Effect, which causes air to be pulled left or right in relation to the rotation of the Earth, the air spins counter-clockwise in the northern hemisphere and clockwise in the southern hemisphere. This affects all objects on earth, and pilots have to account for it when they fly, but it only has a noticeable effect on very large systems like the ocean’s currents, big storms, and hurricanes.
Despite popular belief, the effect is not strong enough to cause toilets to spin in different directions in the different hemispheres or even weather systems like tornados; it really only affects very large weather systems including the constant wind and ocean currents.
To clarify, the Coriolis Effect is real, but the belief that toilets flush in the opposite direction in Australia is a myth. Below we explore the Coriolis Effect and its implications.
Coriolis Effect: IDTIMWYTIM. Does your toilet water drain differently than in the other hemisphere? Is it because of the Coriolis effect? Hank has some things to clarify about these questions and more in this edition of “I Don’t Think It Means What You Think It Means.“
What is the Coriolis Effect?
Air travels across the earth from high-pressure to low-pressure systems creating the wind. Air moves from the equator to the poles, but because Earth is a sphere the poles rotate more slowly than the equator. This causes the air to have a slight bend to the left or right; this is the Coriolis Effect. A good way to think of why it bends in different directions is to imagine that you cut the earth in half horizontally. Looking from below at the top half, Earth will spin clockwise. While looking from above at the bottom half, Earth will spin counter-clockwise. This is the reason why air in the Southern Hemisphere travels through pressure systems with a slight bend to the left, while air in the Northern Hemisphere will travel through the systems with a slight bend right. 
FACT: The Earth spins on its axis from west to east. The Coriolis force, therefore, acts in a north-south direction. The earth spins much faster at the equator than it does closer to the poles, the Coriolis force is zero at the Equator. Learn more at Nationalgeographic.org.
TIP: Although the Coriolis force is useful in mathematical equations, there is no physical force involved. Instead, it is just the ground moving at a different speed from an object in the air.
How the Coriolis Force Acts in Hurricanes
The best way to visually see the Coriolis Effect is to look at a hurricane. The Coriolis force plays a key role in the development of a hurricane. Depending on which hemisphere the hurricane starts in, winds can converge and start the counterclockwise or clockwise rotation around the eye of the storm.
The Coriolis Effect – PBS NOVA. Why do storms spin in different directions depending on their location—and why do they spin in the first place?
How Airlines Take Coriolis Force into Account
Another great example of how we have to account for the Coriolis Force is in flight. Airplanes use the Jet Stream, which only goes from West to East, to travel more efficiently. Although many factors make up the Jet Stream, the directional wind is caused by the left and right deflections of air traveling from pressure systems. If you took a straight-lined flight from Alaska to Florida, you would find yourself far away from your goal because of the deflected wind. If you look at flight paths that airplanes take, they all have an arch to them. This is because while in the air the Earth is still rotating and the “final destination” rotates with it. Airlines are constantly adjusting to the rotation, while also using the Jet Stream to save fuel.
This is a good small scale example of what an airplane does when flying. Pretend the ball is the airplane, the rotation is Earth’s rotation, and the dotted line is your “straight flight”.
Chapter 1: Coriolis Effect.
Do Toilet Flushes Spin in Opposite Directions in Northern and Southern Hemispheres?
The Coriolis Effect does not happen on this small of a scale. The reason why toilets spin the direction they do is due to the way the water jets are aligned and the shape of the basin. However, a study has shown that if you have a big enough tub and no other factors affecting the rotation of the water, it will drain rotating according to the hemisphere, just like a hurricane.
TIP: You are supposed to sync up the two videos below, one was done in the Northern hemisphere and the other Southern. These videos offer real-time proof of the flushing myth.
The Truth About Toilet Swirl – Northern Hemisphere.
The Truth About Toilet Swirl – Southern Hemisphere. The truth is the Coriolis effect doesn’t effect toilet swirls, but the shape of the basin does.