Kinematics Variables Time: temporal characteristics of a performance, either of the total skill or its phases Displacement: length and direction of the path an athlete takes from start to finish Angular Displacement: direction of, and smallest angular change between, the rotating body’s initial and final position Velocity: displacement per unit of time Angular Velocity: angular displacement per unit of time Acceleration: rate of change of velocity Angular Acceleration: angular velocity per unit of time Sport Books Publisher

Kinetics Study of Motion Focuses on the various forces that are associated with a movement Internal Forces: generated by muscles pulling via their tendons on bones, and to bone-on-bone forces exerted across joint surfaces External Forces: acting from without, such as the force of gravity or the force from any body contact with the ground, environment, sport equipment, or opponent Sport Books Publisher

Human Body Models Particle Model: Used when the object of interest (the human body or an object) is airborne after being thrown, struck, or kicked Stick Figure Model: Used when the object is in contact with its environment Rigid Segment Model: Used for more sophisticated quantitative analyses Sport Books Publisher

Three models used to represent the diver Particle Model Rigid Segment Model Stick Figure Model Sport Books Publisher

Types of Motion Angular motion General motion Linear motion Sport Books Publisher

Linear Motion When all parts of the body move the same distance, in the same direction, at the same time Translation refers to movement of the body as a unit without individual segment parts of the body moving relative to one another Rectilinear motion occurs when movement follows a straight line Curvilinear motion occurs when the movement path is curved Sport Books Publisher

Angular and General Motion Angular Motion (rotation) Occurs when a body moves along a circular path, through the same angle, in the same direction, and at the same time The axis of rotation is the point about which movement occurs All joint motions are angular motions General Motion A combination of linear and angular motion Includes most athletic and many everyday activities Sport Books Publisher

Causes of motion The only cause of motion of the human body is the application of an external force Force is any action, a push or pull, which tends to cause an object to change its state of motion by experiencing an acceleration Constant Velocity occurs when an object is not accelerating Linear Motion is caused by forces which act through a body’s centre of mass Angular motion is caused by forces that do not go through the centre of mass Sport Books Publisher

Linear motion results when the forces are applied through the centre of mass Angular motion results when the forces are applied away from the centre of mass

Scalar and Vector Quantities Scalar quantities have only magnitude (time) Vector quantities have magnitude and direction (force) - vectors are straight-line segments with one end defined as the tail and the arrow tip defined as the head. tail head Sport Books Publisher

Adding of Vectors a b + b a = Resultant Resultant The head of a vector points in the direction of the quantity the vector represents Vectors can be added together using the head to tail method - to add vector B to vector A, an identical vector is drawn (same length and direction) as vector B beginning at the head of vector A - the resultant vector is directed from the tail of vector A to the head of vector B a b + b a = Resultant Resultant Sport Books Publisher

Levers Simple machines that augment the amount of work done by an applied force A rigid body (i.e., long bone) that rotates about a fixed point (i.e., joint) called a fulcrum (F) Acting on the lever is a resistive force (R, i.e weight of a limb segment) an an applied force (AF, i.e., muscle contraction). Three classes of levers: a. first class (teeter-totter) b. second class (wheelbarrow) c. third class (screen door with a spring closing) Sport Books Publisher

Sport Books Publisher

Factors affecting the moment of force D A. Balanced teeter-totter B. Increasing the moment arm by leaning backwards C. Increasing the applied force by adding a friend

Calculating net external force using free body diagrams