Linear Kinematics - notes for biomechanics with examples of formulas and definitions PDF

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notes for biomechanics with examples of formulas and definitions ...

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Linear Kinematics September 12, 2019 Kinematics:  Is the study of bodies in motion without regard for the causes of that motion o Position o Distance o Speed / velocity o Acceleration o Jerk  Most human movement is general motion o A complex combination of linear and angular motion in 3D space  Planar motion o Motion that occurs within a single plane (2D) Linear Kinematics  Pure linear motion involves uniform motion with all parts moving in the same direction at the same speed o This motion occurs along a line Angular Kinematics:  Angular or rotational motion occurs when particles within a body have rotated with respect to the center of that body or reference frame o All parts may not be moving in the same direction or at the same speed Position:  Position (S) is the location of a body in space o We use the cartesian coordinate and Newtonian reference system to describe this location o The position is always relative to some origin Displacement:  Displacement (d) is the term used to describe the straight line that connects a points position from one point in time to another d=ΔS=Sf –Si Distance:  Distance (d) quantifies the total movement of any object along a path

Velocity & Speed:  Velocity (v) is the rate of change in position or displacement over time V = ΔS = Sf - Si = d Δt tf - ti = Δt

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Speed (s) is the rate of change in distance over time

Constant Velocity:  When net force on a body is zero, that body will continue to move with a constant linear velocity o If velocity, initial position and line of motion are known; one can determine that body's position and displacement at any point in time until a non zero resultant force is applied Sf = Si + viΔt d= viΔt Velocity & Direction:  The sign of a velocity value indicates the direction of travel o Vx = 1m/s → moving at a rate of 1m/s to the right o Vx = - 1m/s → moving at a rate of 1m/s to the left o Vy = 1m/s → moving at a rate of 1m/s up o Vy = - 1m/s → moving at a rate of 1m/s down Acceleration:  Acceleration (a) is the rate of change in velocity a = Δv = vf - vi Δt = tf - ti 

Jerk (j) is the rate is change in acceleration j= Δa = af - ai Δt tf - ti

Acceleration & Direction:  The direction of acceleration does not indicate the direction of travel  There are 6 cases of acceleration and direction 1) Speed up in positive direction = positive acceleration 2) 3) 4) 5) 6)

Slow down in positive direction = negative acceleration Speed up in negative direction = negative acceleration Slow down in negative direction = positive acceleration Reverse directions from positive to negative = negative acceleration Reverse directions from negative to positive = positive acceleration

Constant Acceleration:  Constant linear acceleration occurs when the net force acting on a body is constant o If the acceleration, initial velocity and initial position are known; one can determine the position and velocity of a body at any point in time until the applied force changes...