Angular Kinetics - continued
TORQUE and its EFFECT on LEVERS and EQUILIBRIUM
Significance of Moment Arm length
Eg. A DANCER’s foot placement in preparation for total body rotation around the
vertical Axis. At the initiation of the turn, the torque producing the turn is provided by
EQUAL and OPPOSITELY directed forces exerted by the feet against the floor.
Turning with a smaller distance between the feet (ie. shorter moment arm) requires
greater force production by the dancer. Maximum force is thus required when turning
About a single support foot, as the moment arm is merely the distance between the
metatarsals and the calcaneus.
COUPLE: A pair of equal and oppositely directed forces that act on opposite sides of
an axis of rotation in order to produce torque. (The torque generated by a couple is
thus the sum of the products of each force and its moment arm).
In the human body, the moment arm for a muscle with respect to a joint center is the
perpendicular distance between the muscle’s line of action and the joint center.