## Kinetic energy

Kinetic energy is used to measure the power of a punch or a kick, which is expressed in an unit named Joule.

It can be defined as energy generated by a moving object or as the work on an object made by a force.

It is calculated by the formula:

 Kinetic energy = Mass • v² = Joules

This formula may be also decomposed this way:

Work = Kinetic energy = Force • distance

The force is defined by Newton's second law:

Force = Mass • Acceleration

In a stationary position, we have potential energy which is translated to kinetic energy for the body while we deliver a strike.

Kinetic energy is connected to power and is not a separate concept. The larger the muscle mass of the arm or leg, the greater the required force will be to move it to the target. The faster you need to move an arm or a leg, the greater the need to accelerate will be and consequently greater force will be needed as well.

For a punch or a kick, kinetic energy depends on the mass and speed, where speed is a more influential variable. If the mass of the punching arm increases twice, kinetic energy is increased twice. But if its speed is doubled, kinetic energy is increased to the square (which is in this case four times more energy).

For simplicity, we confine ourselves in this example to the arms and legs. In reality, during a strike, we also use other body muscles such as knees, thighs, chest and shoulders. Power punching is generated from the ground up to the arms, where the whole body moves as an unit throughout the punch.

A small and light person who gives a fast punch will have approximately the same kinetic energy as that of a big and heavy person who gives a slower punch.

The size of the area over which the energy is distributed influences its impact. Kinetic energy is more effective at penetrating and breaking things when concentrated on a smaller area (as in the case of a bullet).

A punch making contact with just the two knuckles, an area of about one square inch, can represent about 85 times as much energy per square inch than a punch making contact with the entire face of the fist, in this case an area of about eight square inches.

Some factors must be taken into account for a punch having maximum power:

• The person must be standing in a good balanced position, with one foot forward.
• The waist should turn, coordinating the movement of the torso and shoulders. That helps to transfer the force from the legs to the arms.
• The muscles of the arm should not be forced or contracted because this would reduce the force of the strike. Tension brings the potential energy of a strike back into the muscles of the body. Someone relaxed and free of tension will not waste any energy.
• The fist should reach the target without diminishing the momentum before the impact. Many tend to do so for fear of hurting their hand.
• After the impact, the fist or feet must be retracted as soon as possible to transfer more energy from the body’s motion to the opponent. The force of impact should bounce the fist or feet back immediately.
• The opponent should keep his face still while being hit by the punch. To reduce the energy of strike, someone who gets punched in the face should move in the same direction of the punch. The impact will thus be much smaller because the interaction time of his face with the fist is much shorter.