(W= weight!) (W= weight!) W = m W = m g g

The main force acting on the body is the gravitational force! The main force acting on the body is the gravitational force!

Gravitational force Gravitational force WW applies at the center of gravity applies at the center of gravity CGCG of the body!of the body!

Stability of the body against the Stability of the body against the gravitational force is maintained by the bone gravitational force is maintained by the bone structure of the skeleton!structure of the skeleton!

CGCG depends on body mass distribution! to maintain depends on body mass distribution! to maintain stability stability CGCG must be located between feet, if feet are far apart must be located between feet, if feet are far apart forces in horizontal direction forces in horizontal direction FFxx have to be considered have to be considered

To maintain stability To maintain stability the vector sum of all forces the vector sum of all forces applying at theapplying at the CG CG must be must be zero!zero!

The torque r causes a rotational movement around a pivot point! The torque r causes a rotational movement around a pivot point!

Torque is defined by the Torque is defined by the force force FF applied at the distance applied at the distance r r from the pivot point.from the pivot point.

In rotational equilibrium (no rotation, In rotational equilibrium (no rotation, constant rotation) to maintain stability constant rotation) to maintain stability for a person standing on one leg the for a person standing on one leg the torque requires to shift torque requires to shift CGCG of body of body so, that:so, that:

New CG:New CG:

EXAMPLE: EXAMPLE: FORCES ON THE HIPFORCES ON THE HIP

(a person standing on one leg only) (a person standing on one leg only)

EXAMPLE:EXAMPLE: FORCES ON THE SPINAL COLUMNFORCES ON THE SPINAL COLUMN