bullet tips

when use bullet as the physics engine, I had got these problem: 
1. about Restitution
P :
when the rigid body use simple collision shape such as box, cylinder as their collision shape and moving on a static rigid body, the gravity will  make the rigid object move down into the static rigid body's surface when moving.
A: This may caused  by the Restitution. if the moving rigid body has a high Restitution while the static rigid body has a very low Restitution, try to increase the Restitution of the static rigid body.