Subject: Why does the surface affect the ball bounce height

Hi, I did a project on investigating the factos which will affect the bounce 
height of a basketball. I have found out that temperature, pressure and 
dropping on different surfaces will affect the height. One thing i don't 
understand was the theory behind why will the surface of the ground affect the 
bounce height of the ball. The different surfaces were grass, pebble concrete, 
outside basketball court and also brick. The brick seem to give the height 
rebound whereas the grass gives the lowest. 
Thankyou very much

Re: Why does the surface affect the ball bounce height