The gravity is a constant that you can find in the file NewtonScript2.wdl
define newtonGravity, -550.0;

it is very hard to set that variable to the correct earth value as Game Studio is a dimension less engine. try increasing the value until it feel correct to you.

regard the walls and blooks object newton objects should collide with them, one thing thou Newton will obey the passable and invisible flags. so if you make your wall passable then newton will never see them.

Newton