[img:53443ef2ad]http://www.phy.ntnu.edu.tw/demolab/phpBB/pics/2_2_collision2d.png[/img:53443ef2ad] 1. Find the time when two ball collide : D= R1+ R2 where D=Distance between center of two balls , and R1/R2 is radius of each balls 2. Find the line connect center of two balls. and calculate the component of the velocitry for each ball alone the line connect those two balls. For example : Velocity for each ball is Va and Vb (before collision) Calculate Vap and Vbp. (and another normal component Van,Vbn) 3. It is become a 1D collision problem: ball A with velocity Vap collide with ball B with velocity Vbp . You should be able to calculate velocity after collision for each ball. for example: Vap2=((m1-m2)/(m1+m2))vap+ (2m2/(m1+m2))Vbp and Vbp2=(2 m1/(m1+m2))Vap+((m2-m1)/(m2+m1))Vbp The tangential component is not changed Van2=Van, and Vbn2=Vbn 4. Calculate the vector sum for velocity of each ball after collision Va2=Vap2+Van2 and Vb2=Vb2p+Vbn2 (vector summation)