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= mag

• Pressure: force per unit of area over which the force acts p= F divided by A N/cm2 , Pascals, or psi (lb/in2)

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

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 O2

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)