I did horribly on my AP physics test btw lol
(also got a headache trying to read the wikipedia entry haha)
In: Earth Science
Imagine a rotating disk, like a vinyl record. An object that is sitting on the disk near the centre is only moving “sideways” quite slowly (as in moving sideways as it passes the 12 o’clock position). An object sitting near the edge is moving “sideways” much faster.
So an object that is travelling outwards starts off moving “sideways” quite slowly, but as it nears the edge it must move “sideways” quite fast. So it must have accelerated sideways. We know that force equals mass multiplied by acceleration, so if the object has non-zero mass and non-zero “sideways” acceleration then it must have non-zero “sideways” force.
This “sideways” force is the coriolis force.
Have you ever been on a carousel? One of the old-fashioned ones, with horses and cars and helicopters and whatnot. Slow enough to be safe, fast enough to be entertaining. If you tried to walk a straight line through the center from one end to the other wile the whole thing was spinning, you’d stumble – because of coriolis forces. Moving inward from the outside would mean your body experiences a sideways deceleration (since the outside of the carousel spins faster then the center), and moving outward from the center you’d experience a sideways acceleration. Roughly the same thing applies to a planet – everything **not** moving straight along a circle of latitude will experience the same decelerating or accelerating forces as you on the carousel, depending on the direction of movement.
It’s not a real force, it’s something that shows up when you’re reference frame (the coordinates you’re measuring in) is rotating. Similar to centrifugal force.
If you’re rotating you feel like you’re getting pushed to the outside of the turn. That’s centripetal force. It’s not really there but it feels like it to you because you’re rotating.
If you try to move “straight” outwards on a rotating surface like the earth you’ll tend to drift to one side. It will feel like something is pushing you at right angles to the direction you’re going. That’s Coriolis force. It’s not real either, it shows up because you’re rotating and trying to conserve angular momentum. It’s why big storms spin.
Okay so imagine you shoot a cannon from the North Pole to the equator. You’d expect it to go from middle of Canada right to Mexico, but due to the Coriolis effect (not a force) the cannon ball actually lands in the ocean. Why you ask? Because while the ball is suspended in air the world is still turning. Which changes the landing position the longer it takes the object to land.
The Coriolis Force is a fictional Force that has to do with your frame of reference to explain why things seem like they’re not moving in a straight line while on something that is rotating.
Imagine it this way, say you have a disk (like a CD or DVD) and a marker.
If you took that disk a drew a straight line with the marker from the center to the edge while it wasn’t spinning, you’d get exactly what you expect, a straight line on the disk. You marker’s “trail” is a straight line.
if you did that same exact motion again, but with the disk spinning underneath your marker where you still just move the marker in a straight line while the disk is spinning beneath it, when you see the trail your marker left on the disk, you’ll see that it’s a curved line, because the disk was spinning underneath it.
There’s a gif of this on the Coriolis Force Wikipedia page that is very nice to visualize this.
This essentially explains why from two different frames of reference, it looks like your marker is following two completely different paths, one curved and one straight, even though it’s the same motion.
Say you’re standing in the center of a giant spinning disc. There’s someone else standing on the edge of the disc. Because the outside of the disc has a bigger distance to cover, it rotates faster. You are stationary, only rotating on a single point.
If you throw a baseball to them, as it travels outwards to the edge of the disc, it goes to areas that are rotating faster and faster relative to it, so it will lag behind. But also, when you throw the baseball, it only keeps its momentum from the moment you let go. So when you throw it, it travels in a straight line instead of following the rotation of the disc.
So even if the person standing on the edge threw it to you (who is stationary), they would still miss. The ball would keep their momentum and travel further in the direction the disc is rotating.
Tom Scott has a great video visualizing this in a spinning room. Him and someone else are standing on the edges. As he throws a ball, it looks like it curves to the wall, but you can see from a stationary camera, that it’s actually going in a straight line.
[https://youtu.be/bJ_seXo-Enc?t=183](https://youtu.be/bJ_seXo-Enc?t=183)
[https://youtu.be/bJ_seXo-Enc?t=224](https://youtu.be/bJ_seXo-Enc?t=224)
TLDR; If you throw a ball from the edge of a spinning disc to the center, it goes straight, but looks like it curves because your reference point is spinning.
People explain it well below but I wanted to share a great visualization of it from the Science Fiction TV show [“The Expanse”](https://www.youtube.com/watch?v=ryrGPjyKhO4)
In this scene the person is living on an asteroid that is spinning in circles quickly to mimic gravity, since it is spinning much faster than Earth does, the effect is more pronounced. Good pick up from the special effects department and producers to include this scene.
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