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

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= ma g Pressure: force per unit of area over which the force acts p= F divided by A N/cm 2, Pascals, or psi (lb/in 2 )

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/m 3, English lb/ft 3 Torque: rotary effect of force

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

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

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)

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

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 O 2

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

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

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

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

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

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