PEP 294: Lecture Notes
III. Kinetic Concepts
Basic Kinetic Concepts
1. Mass (p. 63, 65)
 | Mass: |
- quantity of matter composing a body
- no mass = no mechanical identity
- symbol: m
- standard unit: kg (kilogram)
| Center of mass (COM) |
- a point around which the mass of a body is balanced in all directions
2. Force (pp. 63-65)
| Force: |
- a push or pull acting on a body
- cause of motion
- the main mechanical quantity of interest in kinetics
- symbol: F
- standard unit: N (Newton)
| Properties: magnitude, direction & point of application |
| Examples: muscle force, weight (gravity), friction, etc |
3. Pressure (pp. 67-69)
| Pressure: |
- amount of force acting over a unit area:
P = F / A
- standard unit: Pa (Pascal) = 1 N/m2
| Examples: high-heel shoe, snow shoe, shin protector, etc. |
Mechanical Loads on the Human Body (p. 73-79)
1. Types of loading
|
Types: |
- Compression: pressing or squeezing force directed axially through a body
- Tension: pulling or stretching force directed axially through a body- Shear: force directed parallel to a surface
- Bending: asymmetric loading that produces tension on one side of a body's longitudinal axis and compression on the other
- Torsion: load causing twisting of a body around its longitudinal axis
| Combined loading: combination of different types of loading |
| Acute vs. repetitive: |
- likelihood of injury: load magnitude vs. frequency
2. Mechanical Stress and Strain
|
Mechanical stress: distribution of force inside of a solid body |
- pressure: distribution of force external to solid a body
- examples: lumbar vs. thoracic vertebrae
| Strain: deformation due to stress |
|
Load-deformation curve (stress-strain curve): |
- yield point (elastic limit): permanent deformation
- failure point: loss of mechanical continuity