Basic Concepts Related To Kinetics

1. Basic Concepts Related To Kinetics • Mass: quantity of matter contained in an object • Inertia: tendency of a body to resist a change in its state of motion • Force: push or pull; the product of mass & acceleration F = ma • Net Force: resultant force derived from the composition of two or more forces

2. Basic Concepts Related To Kinetics • Center of Gravity: point around which a body’s weight & mass are equally balanced in all directions • Weight: attractive force that the earth exerts on the body wt= mag • Pressure: force per unit of area over which the force acts p= F divided by A N/cm2 , Pascals, or psi (lb/in2)

3. Basic Concepts Related To Kinetics • Volume: space occupied by a body; cubic centimeters, cubic meters, liters • Density: mass per unit of volume;  = mass/volume • Specific Weight: weight per unit of volume; metric N/m3, English lb/ft3 • Torque: rotary effect of force

4. Basic Concepts Related To Kinetics • Impulse: product of force and the time over which the force acts; Impulse = Ft

5. Size, Mass & Movement Forms • Variety of life forms on earth: size, shape and styles of locomotion • Although this diversification of life forms may seem to be arbitrary….this is far from true

6. Size, Mass & Movement Forms • There are highly systematic relationships between: • Body mass and body surface • Body weight and lung volume • Body mass and heat production • Body mass and speed • Basic geometric relations are fundamental for form and function (see example of cubes)

7. Size, Mass & Movement Forms • Some physiological processes depend on the area of body, others depend on the body’s volume • Air resistance is a function of surface

8. Body Size, Energetics & Movement Forms • Size is a key factor for: • energetics • movement speed • gait patterns • Respiratory System: • small insects: diffusion of oxygen • large mammals: development of lungs & blood circulation (active pumping of O2

9. Body Size, Energetics & Movement Forms • Chain of connection: • size of animal ==> type of respiration system ==> basic metabolic rate ==> maximum oxygen uptake ==> energetics ==> movement speed ==> movement patterns

10. Body Size, Energetics & Movement Forms • Relationship between Energetics and Mass: • basic metabolic rate is proportional to body mass • for different locomotory activities there is a systematic relationship between body mass and energy cost

11. Body Size, Energetics & Movement Forms • Movement Speed and Gait Patterns • 4-legged animals: 3 gaits, transitions are always from walk to trot to gallop • 2-legged animals: efficient and maximal locomotory speed is determined

12. Lessons • Movement forms are not chosen arbitraryily • Fundamental physical relationships, e.g., size and mass, determine basic energetic balance • Fundamental energetic capabilities determine locomotory forms

13. Lessons • Preferred movement forms tend to maximize efficiency • Size and mass constrain movement forms

14. Size, Mass & Development • During the development of human infants there are systematic changes in relative proportions (see overhead)