I Can't Believe They're Not Forces!

If you’ve ever taken a Physics course, you may have learned about Newton’s 3 Laws of Motion. In case it’s been a while:

1. An object in motion stays in motion
2. The force of an object is equal to the mass multiplied by the acceleration (F=ma)
3. For every action, there is an equal but opposite reaction.

These are the rules upon which Classical Physics was founded. They are taught in grade school like they are the end-all and be-all of motion in our Universe, and one can certainly do amazing things with them. However, think about this interesting mind experiment: you slide a puck on a frictional rotating table.

That’s it. That’s the mind experiment. You can picture that, right? Because Newton’s Laws can’t.

...pause for dramatic effect...

At least, not in the way they’re presented above. Newton designed his laws to work in a non-accelerating field; something moving on a spinning platform seems to be accelerating in several different directions, and thus makes these laws completely unusable. Physicists didn’t like this. So, to solve this quandary, they manipulated his equations into something that could be used in a rotating field, like our platform. What they developed were two brand new equations of motion: the centrifugal force and the Coriolis effect.

And in reality, there's no cause for either. Neither force is truly there.

Centrifugal Force

This is the thing that Physics teachers adamantly tell you is not real; there’s no such thing as centrifugal force, only centripetal force, so stop mixing the two up. But, of course, this is a lie. They were lying to you.

It's OK.

As one of my sources put it, “Any time the word Centrifugal Force is used, what is really being described is a Lack-of-Centripetal Force.” This is a pretty apt description. The centrifugal force is that feeling you get when making a sharp turn in your car: everyone goes off to one side, faces planted into the window. Obviously, it’s not directly caused by anything; it’s an effect created by the velocity of the spin, as well as the inertia of the object. The combination of the two gives the illusion that you’re being flung out of the car. However, look at the situation from outside of the turning car: all you’d see is someone being flung in their original path of motion, while the force of the car spins them around.

Centrifugal force actually has a pretty big impact, celestially: since the Earth is spinning at such a fast speed, centrifugal force physically pushes the equator out, giving our planet a big of a bulge around the middle. Measuring this bulge is actually a pretty standard method of calculating the rotation period for all sorts of astronomical objects. Cool, no?

The Coriolis Effect

This is the fun one. It’s what makes the toilet flush different directions in different hemispheres, right?

Stop that. It’s embarrassing. This is wrong, but not for the reason you think.

The Coriolis effect is hard to picture without a good imagination. Say that you’re on a giant turntable, right in the center, just spinning around (See? Imagination). You roll a ball away from you, towards the edge of the circle. As you watch the ball, you see it move off to one side, curving away to the right, until it drops off:

That’s the Coriolis Effect at work. Instead of going straight, like you anticipated, the ball curved away. If you were outside of the frame of motion, not spinning with the turntable, the path would be a totally straight line, obeying Newton’s Laws and everything. It’s only when we’re spinning at the same time that the Coriolis Effect has any impact.

Fun fact: these pictures are showing the exact same thing. Mind = blown.

This goes for the rotation of the Earth, too. Airplanes taking off in the Southern Hemisphere drift to the left when they go on long trips because of the Coriolis Effect; planes in the North list to the other direction, for the same reason. Wind currents twist the opposite way, and hurricanes develop different spins. In fact, the Coriolis Effect is a major reason hurricanes develop in the first place. Look at this map charting the paths of tropical cyclones for the last several years:

Notice: not a single one developed on the equator. Why? No Coriolis Effect.  

HOWEVER. This does not mean flushing your toilet in the Southern hemisphere creates a brand-new, never-before-seen spin. The Coriolis Effect, in the grand scheme of things, is incredibly weak; the object needs to be incredibly massive, or going a very far distance, to be affected at all. In other words: nothing happens to your toilet.

Nothing. 

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EDIT: Also, this is cool.