When a ping pong ball strikes the ground obliquely without spinning, the angle of incidence is not equal to that of reflection, am I correct? Here is my thoughts: Assume the ground is smooth and negligible air resistance. When the ball touches the ground, it starts to deform, delivering its momentum to the ground(is it right to say so??) . After a split second, it retains its shape due to its elasticity, applying a force to the ground. A reaction force appears which causes an upward acceleration to the ball. However, due to energy loss as sound, the loss in elastic pe is less than the loss in gravitational pe before the ball reaches the ground. Therefore the upward acceleration is smaller in magnitude than the deceleration during impact. The resultant velocity of the ball after impact thus does not equal that before impact. Please correct my mistakes, if any.