Throwing is all about torque and center of mass.
A standard hip throw begins with the arm of
the attacker (the one being thrown) extended over the right shoulder of
the
defender (the one doing the throwing).
The defender places their right hand on the shoulder of the
attacker and
their left hand on the wrist. The defender
applies a force on the arm by pulling their left hand to
their left
hip. The right hand remains on the
shoulder. As the defender pulls they
turn their body and drop to their right knee.
The
defender must apply sufficient force to
the attacker, and at the correct angle, to throw off the attacker’s
balance. This can be made much easier if
the defender is able to lower their center of mass lower than that of
the
defender. This causes the center of mass
of the attacker-defender system to shift downward.
When the center of mass of the system is
lower, the center of mass of the attacker does not need to be moved as
far in
order to displace it from above the attacker’s base.
http://www.mjjudo.com/images/clipart/throw5.jpg
The force the defender applies causes
torque on the attacker with the attacker’s arm acting as the action arm. If the torque is great enough the attacker’s
center of mass will be offset and they will fall. The
defender dropping to their knee helps
enormously. This action causes the center
of mass of the
defender to drop very quickly and the attacker will not be
able to
stop his or her center of mass from shifting.
It
is obvious that a large person would be
difficult for a smaller person to throw.
The main reason for that is that the larger person’s mass is so
great. However, another aspect that
contributes to the increased difficulty is the length of the attacker’s
arm. Larger people tend to have longer
arms, creating a longer action arm. The
longer the action arm, the higher the moment of inertia.
The higher the moment of inertia, the larger the
torque required to move the attacker.