KIN 3309 1nd Edition Lecture 15 Outline of Last Lecture I II III IV V VI VII VIII IX X XI XII XIII XIV Angular Kinematics Types of Angles Calculating Absolute Angles Calculating Relative Angles Angular Position Distance Displacement Angular Motion Vectors Angular and Linear Motion Angular and Linear Velocity Tangential Velocity Maximize Linear Velocity Tangential Acceleration Centripetal radial Acceleration Angle Angle Diagrams Quiz Outline of Current Lecture I Outline II Kinematics vs Kinetics III Sources of Forces Affecting Human Movement IV Force V Composition and Resolution of Forces VI Newton s Laws of Motion VII Newton s 1st Law Law of Inertia VIII Newton s 2nd Law Law of Acceleration IX Newton s 3rd Law Law of Action Reaction 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 X Momentum XI Center of Mass XII Gravity Noncontact Force XIII Weight XIV Contact Forces XV Ground Reaction Force GRF XVI Center of Pressure COP XVII Linear Kinetics of Locomotion XVIII Joint Reaction Force JRF XIX Inertial Force XX Muscle Force XXI Elastic Force XXII Quiz Current Lecture I Outline a Force i External internal inertia b Newton s laws of motion c Momentum d Center of Mass e Gravity f Weight g Types of contract forces in human movement i Ground joint reaction force inertial force muscle force elastic force friction II Kinematics vs Kinetics a Kinematics i Examines spatial space and temporal time characteristics of motion 1 Position displacement velocity and acceleration ii The forces causing the motion are not considered b Kinetics i Deals with the cause of motion force ii The concept of force is the basis for understanding linear kinetics iii Linear kinetics deals with the causes of translator motion III Sources of Forces Affecting Human Movement a External environmental i Gravity ii Impacts collisions iii Ground object contact reactions normal shear iv Fluid air water etc Pressure Viscosity b Internal Biological i Muscle contraction ii Biomaterial properties strength elasticity inertia iii Fluid air pressure c Inertia i The resistance of any physical object to any change in its state of motion including changes to its speed and direction IV Force a Forces alter the motion and or change the shape of an object b Forces have both magnitude and direction i Vector c Forces have points of application and lines of action d Force has units of Newtons N which is kg x m s2 V Composition and Resolution of Forces a VI Newton s Laws of Motion a Published 1687 b Basis for most analyses in biomechanics c Laws demonstrate how and when a force creates motion VII Newton s 1st Law Law of Inertia a A body tends to stay at rest or in uniform motion unless acted upon by an unbalanced external force b Overcoming inertia requires a net external force greater than the objects inertia c To initiate movement the external force must positively accelerate the object d To stop movement external force must negatively accelerate the object e Greater mass greater inertia requiring larger external forces VIII Newton s 2nd Law Law of Acceleration a The change of motion of a body is proportional to the force impressed and is made in the direction of the straight line in which that force is impressed b Force mass x acceleration IX Newton s 3rd Law Law of Action Reaction a For every action there is an equal and opposite reaction on different objects i The mutual actions of two bodies upon each other are always equal and directed to contrary parts X Momentum a Inertia in motion or mass in motion b Carries the notion of both mass inertia and velocity motion i tendency of an object to remain in motion ii An object with momentum is going to be hard to stop iii To stop an object with momentum it is necessary to apply a force against its motion for a given period of time impulse c Momentum mass x velocity i Momentum is in the same direction as the velocity ii Momentum is a vector iii Momentum is the quality of motion of an object iv Symbolized as p v Units kgm s or Ns vi Therefore with constant mass to change momentum an external force must be applied d Conservation of Momentum i In a system of bodies that exert forces on each other the total momentum in any direction remains constant unless some external force acts on the system in that direction XI Center of Mass a The center of mass is the mean location of all the mass in a system b The ground reaction force vector acts through the center of mass of the body XII Gravity Noncontact Force a The force of gravity is inversely proportional to the square of the distance between attracting objects and proportional to the product of their masses i Two small objects gravitational attraction extremely small neglect ii However the Earth s mass is considerable iii The force of gravity causes an object to accelerate towards earth at 9 81 m s2 XIII Weight a Weight is the force produced by the acceleration of gravity on an object b Weight DOES NOT equal mass c Weight is a vector quantity i Line of action straight down and point of application CoM XIV Contact Forces a Contact forces result from the interaction of two objects b Contact forces i Ground reaction force GRF ii Joint reaction force iii Inertial force iv Muscle force v Elastic force vi Friction vii Fluid Resistance 1 Viscosity and density XV Ground Reaction Force GRF a If you push against the ground the ground pushes back with a force equal in magnitude but opposite direction Newton s 3rd Law b GRF is commonly measured using a force platform XVI Center of Pressure COP a In biomechanics COP is the term given to the point of application of the GRF vector XVII Linear Kinetics of Locomotion a Initial peak rises above BW as weight bearing takes place b 2nd peak active push against ground to move into the next step c XVIII Joint Reaction Force JRF a The force experienced at a joint b A common biomechanical analysis is a link segment analysis i Each segment is considered separately c The net force acting across the joint can be determined from the kinematic and kinetic analyses XIX Inertial Force a Force opposite in direction to an accelerating force acting on a body b In many instances in human movement one segment can exert a force on another segment c Movement not caused by muscular action d Generally proximal distal e E G ankle motion during running i Ankle angle at take off and touch down ii Leg swing exerts inertia force on foot