Angular Kinetics and Biomechanics

Angular Kinetics

Center of Mass

Point around which mass or weight is considered to be concentrated.

Determining COG

• Balance method
• Suspension method
• MRI reconstruction
• Segmental

Segmental Limitation

• Based on Caucasian male cadavers
• Completed in 1930s
• Based on segments being truncated cones

Mechanical Stability

Ability to maintain vertical projection of CG within base of support.

Ways to Increase MS

• Increase mass
• Increase friction between body and surface
• Increased size of base support

Angular Inertia

Property of an object to resist changes in its angular motion.

Factors Influence

Radius has larger influence than mass.

Center of Mass

Point where gravitational force is applied balance

Radius of Gyration

Point where mass can conceptually be concentrated such that it does not alter moment of inertia. Closer mass is distributed to axis of rotation easier it is to rotate. The resistance to angular inertia is reduced.

Angular Momentum

Angular analog of linear momentum, quantifies angular motion of object

H=mk^2w

1st Law Angular

Angular momentum of isolated system will remain the same regardless of any movements or torques as long as no external torque is applied.

2nd Law Angular

Change in angular momentum of an object is proportional to the net external torque exerted on it, and this change is in the direction.

3rd Law Angular

Torque generated by one body part to rotate that part results in a counter torque by another body part.

Mechanics of Biology

Stress

Force internal per unit area over which the force acts.

Strain

Mechanical stresses cause strain. Deformation of a material with external force g=(L2-L)/L

Viscoelasticity

Stiffness and strength depend upon speed of applied load higher loading rate = increased stiffness. Lower load = decreased stiffness. High load, few reps. Low load, many reps.

Forces

Uniaxial

• Compression
• Tension
• Shear

Combined

• Bending
• Torsion

Anisotropy

Stiffness & strength depend upon mode of loading.

Bending

• Three point bending
• Cantilever bending

Bone Remodeling

Alters size, shape & structure based on the imposed mechanical demands. As age progressive decrease in bone density, lower collagen & mineral content, lower mass, size.