Coriolis Simulator

The Coriolis force is the classic example of something that feels like a force but isn’t one. This demo is the merry-go-round thought experiment from my post on the Coriolis effect, made clickable.

What you’re looking at

Click anywhere and a ball launches from the middle of the disk, straight at the point you clicked. The ochre ring marks the spot you aimed at. It’s painted on the disk, so it rides around as the disk turns.

You’ll miss. Every time.

Now tick “show the non-spinning view”. Same ball, same throw, same physics, but the path is dead straight. It always was. Nothing ever pushed the ball sideways.

The point

The ball travels in a straight line the whole time. What curves is you. The disk rotates beneath the ball while it’s in flight, so from where you’re standing the ball appears to swerve. That apparent swerve is the Coriolis effect.

It’s called a fictitious force for exactly this reason: it’s an artefact of watching from a spinning frame, not a real push. And it’s not a small effect. Scale the disk up to a planet and it’s what makes hurricanes spin and ocean currents swirl.

Flip the spin slider negative to reverse the disk’s rotation, and the deflection flips too. That’s the same reason storms rotate one way in the northern hemisphere and the other way in the southern.