This does not look like the Newton PH-Engine. It's the build in engine of Gamestudio(you added the prefix NEWTON to your post, remove it. you dont need it for build in related questions)

Dont use the gravity for entity movement. Gravity is a var you want to change if there is a differen gravitation. This var is global(counts for all entities).
use phent_addcentralforce instead.

GReets
Rackscha