KIN 3309 1nd Edition Lecture 16 Outline of Last 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 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 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 XIX Inertial Force XX Muscle Force XXI Elastic Force XXII Quiz Outline of Current Lecture I Newton s Laws of Motion II Momentum Weight COM III Contact Forces IV Outline V Free Body Diagrams VI Effects of a Force at an Instant in Time VII Friction VIII Impulse Force Applied over a Period of Time IX Work Force Applied over a Distance X Power XI Energy XII Work Energy Theorem XIII Conservation of Energy XIV Energy Conversion during Gait XV Quiz Current Lecture I Newton s Laws of Motion a 1st Law Law of Inertia i A body tends to stay at rest or in uniform motion unless acted upon by an unbalanced external force b 2nd Law Law of Acceleration i Force mass x acceleration rd c 3 Law Law of Action Reaction i For every action there is an equal and opposite reaction on different objects II Momentum Weight COM a Momentum i Inertia in motion or mass in motion ii The quantity of motion of an object b Weight i Weight is the force produced by the acceleration of gravity on an object weight does not equal mass c Center of Mass COM i The mean location of all the mass in a system III Contact Forces a Ground Reaction Force GRF i Force exerted by the ground on a body in contact with it b Joint Reaction Force i Force experienced at a joint c Inertial Force i Force opposite in direction to an accelerating force acting on a body d Muscle Force i Force when muscle fibers generate tension e Elastic Force i The tendency of solid materials to return to their original shape after being deformed IV Outline a Free body diagram a k a force diagram b Effects of a force at an instant in time c Types of contact forces in human movement i Friction d Impulse e Work f Power g Energy h Work Energy Theorem i Conservation of Energy V Free Body Diagrams a Called a force diagram i To analyze the forces linear and moments angular acting on a body ii Display magnitude and direction of forces VI Effects of a Force at an Instant in Time a If acceleration is zero biomechanical study of the human is referred to as a static analysis b If acceleration is not zero and is significant biomechanical study of the human is referred to as a dynamic analysis c Static Analysis i Systems at rest or constant velocity d Dynamic Analysis i Systems in motion accelerating or decelerating VII Friction a Friction is the force acting parallel to the interface of two contacting surfaces during motion or impending motion i The normal force is important b The normal force is the force acting perpendicular normal to the surface i Newton s 3rd Law La w of Action Reaction ii Often simply the weight of the object in the direction c The coefficient of friction is greater when an object is not moving d Friction for a given object is not affected by the surface area in contact VIII Impulse Force Applied over a Period of Time a An object with momentum can be stopped if a force is applied against it for a given amount of time b Force applied over a period of time impulse change in momentum c Impulse is vector quantity the direction is the same as the direction of the force d Symbolized as I e Units kgm s or Ns IX Work Force Applied over a Distance a Work Force x Distance b The scientific definition of work is using a force to move an object a distance when both the force and the motion of the object are in the same direction c Units of work are Joules 1 J 1 Nxm d Work is a scalar quantity e Work is not a function of time X Power a Power is the rate at which work is done b c d e Power work time Also power force x velocity Units of power are Watts W J s Power is a scalar quantity XI Energy a Energy is the capacity of a physical system to perform work b Kinetic Energy KE results from motion c Potential Energy PE results from position in gravitational field d Units of energy are Joules J e Energy is a scalar quantity f Strain elastic energy SE is the capacity to do work due to deformation of a body XII Work Energy Theorem a The work done by a resultant force is equal to the change in energy that it produces b This is assuming that no work is done to deform the system i e no strain energy is stored c This also assumes that no work is done to increase rotational kinetic energy XIII Conservation of Energy a The total energy of a closed system is constant since energy does not enter or leave a closed system b This only occurs in human movement when the object is a projectile and we neglect air resistance i TE PE KE c Note that gravity does not change the total energy of the system Energy Conversion during Gait a Walking and running are characterized by energy conversions i Walking 1 Kinetic potential energy conversion ii Running 1 Kinetic and potential energy are converted to elastic and viceversa XIV XV Quiz a If the static coefficient of friction of a basketball show on a particular playing surface is 0 58 and the normal force is 911 N what horizontal force is necessary to cause the shoe to slide i 528 38N b The limiting fiction between the 25 kg bag and the cart is 50 N You need to slide the bag to the side of the cart If you apply 50 N horizontally on the bag i The bag will remain motionless ii The bag will begin to slide iii The bag will rise off the cart iv Need more info to calculate v Friction force is 50 N you are applying the same exact amount of force Quiz 2 Chapter 8 10 is 98 of the quiz Definitions o Kinetics kinematics angular velocity relative angle joint angles and that impulse is change in momentum etc Example 5 Dynamic Analysis Questions will be on the quiz