Lecture 7 Outline of Last Lecture I. Fundamentals II. Lever Systems III. Mechanical Advantage IV. The Three Levers V. Dimensions Used in Biomechanics VI. Newton’s Laws of Motion VII. What Causes Motion? VIII. Forces Acting on Human Body IX. Torque X. Stability and Stress Outline of Current Lecture I. What Causes Motion? II. Forces Acting on Human Body III. Torque IV. Stability and Stress Current Lecture H. What Causes Motion? 1. Push or pull a. muscles can only pull 2. Tend to produce acceleration HPER 205 1st Edition These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best !used as a supplement to your own notes, not as a substitute. !3. Internal/external factors and muscle and forces I. Forces Acting on Human Body 1. Gravity (weight) a. constantly accelerating us downward b. rate of acceleration = -9.81 m/s^2 c. weight = force due to gravity - mass x gravity 2. Ground reaction forces a. newtons 3rd law 3. Friction: horizontal component of GRF 4. Fluid forces (eg. air resistance) 5. Muscle forces: internal to the body J. Torque 1. Def: the rotary effect of a force a. Units = Nm 2. To combat the effects of external forces, muscle forces are used to generate torques 3. Quantifying Torque a. T = force x distance b. moment arm (d): the perpendicular distance between the line of action of a force and an object’s axis of rotation K. Stability and Stress 1. Stability a. Factors increasing stability - increase body mass - increase friction - increase base of support- height of CG - horizontal position of CG in relation to base of suport 2. Mechanical Stress a. ó = F/A - internal force divided by the cross sectional area of the surface b. Types: - compressive + object deforms + shortening in the direction of the force + gravity - tensile + stretching or elongation of the object + lengthening in the direction of the force - shear + transverse (parallel to surface) + sliding (friction) - bending + compressive force acting off center from the long axis + compression on one side and tension on other side - combined + combo of loading forms + bones = compressive, tensile, shear,
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