9 9 14 biomechanics class notes Basic kinetic concepts o Center of mass center of gravity Imaginary point about which all the mass weight of a body is distributed In human body approximately at the level of the naval top tobottom and midway front to back o Weight Attractive force that the earth applies to a body Equal to the mass of a body in kg times the acceleration due to gravity 9 81 m s 2 W mg o Inertia o Mass Quantity of matter that makes up body Representing vectors o Vector quantities such as forces are represented graphically using arrows o Length of the arrow denotes the magnitude of the vector o Orientation of the arrow denotes the direction of the vector Things to do o Get textbook o Read ch 1 o Do units reading on moodle o Start ch 8 o Print out and read handout for first lab on Moodle Linear Kinematiics of Human Movement ch 8 o Basic kinematic quantities Position Displacement Distance Velocity Speed Acceleration o Differentiation integration Kinematics o Physics o Mechanics o Dynamics o Kinematics o Kinetics Quantitatively and systematically describing motion Linear kinematics o The description of linear motion there is either no rotation or it is not explicitly considered o Scalars vectors Scalar A quantity that has magnitude only Vector A quantity that has magnitude and direction Examples 30 mph is a scalar 30 mph heading due east is a vector quantifying human motion o when someone moves runs walks jumps how can we quantify their motion o You can determine who a person is by the way they move o You pick up abnormal gait movement immediately Meaningful phases of movement o To facilitate analysis it is common to divide a movement sequence into two or more phases o Stance and swing phases of the human gait cycle o Running no time when both feet are on ground o Walking always have at least one foot on ground Discrete activities o Forehand shot in tennis o Do task wait respond to next stimulus o Define with key 3 phases Preparation Action Follow through o 1 Prepare racket o 2 Bring racket forward o 3 Finish swing with ball leaving racket follow through temporal analysis o the time spent I each phase is one of the most basic descriptions of a movement sequence frames of reference o global reference frame o also called inertial fixed or laboratory reference frame o Absolute position of the pelvis in a global reference Collecting kinematic data o Many different types of systems exist for data collection Electrogoniometers Accelerometers Electromagnetic tracking Optoelectronic systems Video based systems Cameras track reflective markers placed on body segments Linear position o Where a point of interest in at a given instant in time o Must be expressed in an established reference system Position s Displacement d s Velocity v d t s t Acceleration a v t Position o Where something is at a certain point in time o Position 1 position 2 etc Linear displacement distance o Linear displacement a vector is the straight line change in position from initial position to final position o linear distance a scalar is measured along the actually path of motion o distance can be greater than the magnitude of the displacement displacement distance o both have dimensions of length metric SI meter kilometer cm English inch foot yard mile o Linear distance Scalar quanitity no direction specified o Linear displacement Vector quantity length direction required E g left right up down north south east west positive negative
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