TaeKwon-do has a great variety of kicks.  All the kicks create momentum. Some create linear momentum and some rotational.  All of the hundred of kicks are variations on four basic kicks. 

Front snap kick -- Rotational                     Side Piercing Kick -- Linear
Side turning kick -- Rotational                  Turning Back Kick -- Linear

ROTATIONAL

• Front Snap Kick- -The target for a front snap kick is generally the groin.  First the attacker raises their leg so that the upper leg parallel with the floor and lower leg is perpendicular.  The lower leg is then snapped upward pivoting at the knee.  This creates an upward angular force.  The knee should be slightly bent on impact in order to have the highest acceleration and therefore the greatest force.

• Side Turning Kick- -Side turning kicks are preformed in much the same way as the front snap kick.  The difference is that the hips are turned to one side creating an attack from the side.   The target for this kick is either the ribs or the head.  As with the front snap kick, the leg is raised while bent at the knee. For this kick however, the whole leg should be parallel with the floor.  It is then rotated at the knee until it reaches the target.

 
The torque, or rotational force, behind the rotational kicks can be found using the rotational version of Newton’s Second Law :

α = angular acceleration

The moment of inertia can be found by multiplying the length of the action arm by the mass of the object.  In the case of the front snap kick, it is difficult to increase either the length of the action arm, in this case the lower half of the leg, or the mass of the leg.  Therefore in order to increase the torque generated by the front snap kick, the acceleration of the leg movement must be increased.

Increasing the torque of a side turning kick is somewhat easier.  The mass cannot be changed but the leg can be straightened as it begins to move creating a much longer action arm.  Acceleration can also be increased to help create more torque.

The attacking tool for both kicks is the ball of the foot.  This is a relatively small area for the force to act over which will help to increase the pressure on the target.

LINEAR

• Side Piercing Kick- -The side piercing kick consists of a linear motion.  When performing this kick, the leg is raised with the knee bent and pulled into the chest, parallel to the floor.  The heel of the foot should be in line with the hip joint.  The leg is then straightened keeping the heel in line with the hip throughout.  The knee should be bent slightly at the moment of impact.
  

• Turning Back Kick- -This kick begins with a step.  The stepping foot then becomes the pivot foot.  The other foot is then raised underneath the body with the toes pointed down and the heel directly below the hip joint of the same leg.  The leg is then extended straight back with the heel of the kicking foot remaining in the same line.

 

The force generated by a side piercing kick and a turning back kick can be calculated using Newton’s Second Law :

More force is generated by a side piercing kick than either a front snap kick or a side turning kick because it is easier to add more mass to the equation.   This extra mass comes from the attackers body moving forward.  Acceleration is more difficult to increase in this kick however because more mass is being moved.  The attackers body mass can also be added to the force creating mass in the turning back kick.  But again, more mass is being moved so the acceleration is harder to increase.

The attacking tool for both oh these kicks is the foot sword.  This is also a relatively small area.  Therefore the pressure on the board will be fairly great.