For example: conser vation of momentum m1v1+m2V2=m110+m2V20 Sm11+m212=m1v10+m2120 2. Gal i leo relativity P957P957 S 1 1 2 2 1 10 2 20 m v m v m v m v     + = + S 1 1 2 2 1 10 2 20 m  v + m  v  = m  v  + m  v      For example：conservation of momentum 2.Galileo relativity