[BDPW]

You're conflating coordinate and proper acceleration.

[marcus_holmes]

I don't think I understand the difference. I have always been told that acceleration is change in velocity over time. Is that wrong? Are there other types of acceleration?

[magicalhippo]

> I have always been told that acceleration is change in velocity over time. Is that wrong?

Not per se, but it's more complicated when relativity gets involved.

Wikipedia has some decent starting points:

https://en.wikipedia.org/wiki/Proper_velocity

https://en.wikipedia.org/wiki/Proper_acceleration

https://en.wikipedia.org/wiki/Four-acceleration