An efficient method is proposed for hair animation. The movement of hairs is modeled by simplified physical simulations. In particular the method can treat successfully collisions between hair and a human body or other objects, which provides realistic hair animation. The fast collision detection is achieved using cylindrical representation of the head and human body parts, despite a large number of hairs. The cylindrical representation allows collision detection to be performed by table look-up and interpolation, which assures that the computation time is independent of the complexity of the objects. A reaction constraint algorithm is also applied for the collision reaction to simulate inelastic contact. The efficiency of the method is well illustrated by the animation obtained