9/9/14 biomechanics class notes- Basic kinetic conceptso 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-to-bottom, and midway front to backo 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= mgo Inertiao Mass Quantity of matter that makes up body- Representing vectorso Vector quantities, such as forces, are represented graphically using arrowso Length of the arrow denotes the magnitude of the vectoro Orientation of the arrow denotes the direction of the vector- Things to do:o Get textbooko Read ch. 1o Do units reading on moodleo Start ch. 8o 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 Accelerationo Differentiation & integration- Kinematicso Physicso Mechanicso Dynamicso Kinematicso Kinetics Quantitatively and systematically describing motion- Linear kinematicso 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 motiono when someone moves (runs, walks, jumps…) how can we quantify their motion?o You can determine who a person is by the way they moveo You pick up abnormal gait/movement immediately- Meaningful phases of movemento To facilitate analysis, it is common to divide a movement sequence into two or more phaseso Stance and swing phases of the human gait cycleo Running: no time when both feet are on groundo Walking: always have at least one foot on ground- Discrete activitieso Forehand shot in tenniso Do task, wait, respond to next stimuluso Define with key 3 phases Preparation Action Follow througho 1. Prepare racketo 2. Bring racket forwardo 3. Finish swing with ball leaving racket/follow through- temporal analysiso the time spent I each phase is one of the most basic descriptions of a movement sequence- frames of referenceo global reference frameo also called; inertial, fixed, or laboratory reference frameo Absolute position of the pelvis in a global reference- Collecting kinematic datao 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 positiono Where a point of interest in at a given instant in timeo Must be expressed in an established reference system- Position - s- Displacement – d= s- Velocity = v = d/t = s/t- Acceleration = a = v/t- Positiono Where something is at a certain point in timeo Position 1, position 2, etc.- Linear displacement & distanceo Linear displacement (a vector), is the straight line change in position, from initial position to final positiono linear distance (a scalar) is measured along the actually path of motiono distance can be greater than the magnitude of the displacement- displacement & distanceo both have dimensions of length metric (SI): meter, kilometer, cm English: inch, foot, yard, mileo Linear distance Scalar quanitity: no direction specifiedo Linear displacement Vector quantity: length & direction required E.g. left, right, up & down, north, south, east, & west, positive &
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