To illustrate the effect of speed on power, try this. Throw a rubber band as hard as you can at a friend's arm. Ask the friend if it hurt? Now hook the rubber band over a finger, pull it back, and shoot it at the friend's arm. No need to ask this time; the friend will probably let you know that it hurt. Speed hurts!
Newton’s Second Law of Motion, expressed in the formula f= ma, states that the force acting on an object is equal to the product of the mass and acceleration of the object. This force is then available for transfer to another object, such as an opponent's body. Using this formula, we see that it is possible for a small, high velocity bullet to have the same striking force as a large, slow moving locomotive. In a punch, since the mass (m) of the fist is constant, the only option available to increase its striking force (f) is to increase its acceleration (a). Therefore, the acceleration of a fist is more important than its mass or the mass of the body behind the fist.
Acceleration is the rate of change of velocity with respect to time. Increasing the velocity of the fist over time increases its acceleration. The distance from the starting position of the fist to its point of impact affects the amount of time available for its acceleration. The greater distance the fist has to travel, the greater its velocity and acceleration and thus the greater its striking force. A reverse punch thrown from the hip has more power than a jab thrown from the on-guard position.
For greater speed in a technique, move the body first, then arms and legs. They move faster than the body and will quickly move ahead of the body.