Why, then, move should the karateka swing his or her hand with as much velocity
as possible? Because if the hand is moving quickly, it is likely to decelerate (strictly
speaking, accelerate in the direction opposite to its direction of travel) more quickly in
response to the force the board exerts on it upon collision, as per Newton’s third law.
If the amount of time involved in the transfer of momentum is therefore small, the
amount of force that will be transferred to the target all at once will be large. This
sudden transfer of a lot of force causes the part of the board that is struck and which
therefore experiences that force to accelerate. If that part of the board accelerates.