Gravity on moving sprite

Hello! Thank you for taking your time to hopefully help me!

This is my very first project with Construct 2 and while I'm learning pretty fast, I have a little fight with this simple thing.

I want to add some gravity (pulls towards the ground) to my working superball! <img src="smileys/smiley36.gif" border="0" align="middle" />

Here's my setup for now:

<img src="http://img842.imageshack.us/img842/4831/88408243.png" border="0" />

But now it moves in straight lines.

BS = ballspeed

S_obstacles are mainly players objects which are round.

L_obstacles are walls around the scene (and the ground).

I hope I make sense <img src="smileys/smiley9.gif" border="0" align="middle" />

Thank you!

Why not just add a physics behavior to you ball ?

Well, I don't know.

I didn't successfully found a way to make it bounce back according to the round objects I use.

I'll play some more with it :)