[thedjinn]

Exactly. The general idea is that you get a measurement of the applied force, so integrating that value gives you an approximate velocity.

[mikewhy]

Assuming you worked on the app based on your other replies. Is 3D Touch applicable here?

[thedjinn]

Yes, that works. However, you would be facing the same problems. You can read out the pressure of a touch but the initial pressure is not the strongest since the finger is still in motion. Additionally, 3D touch is not supported on all devices.

Another interesting thing is that there are also private APIs for reading out the estimated finger size of a touch. This can give you even more information to determine the velocity from, as light touches are usually done with the fingertips.