精灵套装球弹跳物理目标c

I want to add gravity to ball, so it will bounce up and down, and slightly to right or left in which angle ball bounces to, and i don't want to lose ball energy, so it bounce always in same height. For now ball bounce in every direction and stops after few min even if i set friction on 0. Here little bit of my code :I want to add gravity to ball, so it will bounc