[jeremyvisser]

The difference is very simple:

Apple uses the derivative (i.e. rate of change) of acceleration, while all the other (ineffective, in my experience) third-party apps simply use acceleration.

People with motion sickness can deal with speed just fine. While relaxing on an equatorial beach, you’ll have no qualms hurtling around the poles at 1600 km/h.

Acceleration is also perfectly fine for motion sickness. Most people are being pulled towards the centre of the earth at 1.0 G with no complaints whatsoever.

But the significance during motion sickness is the rate of change of the rate of change. That thing where the vehicle slows down, turns a corner, goes over a bump.

This is why Apple’s motion cues actually work, because they use what actually matters for motion sickness.