KIN 3309 1nd Edition Lecture 17 Outline of Last Lecture I. Newton’s Laws of MotionII. Momentum, Weight, COMIII. Contact ForcesIV. OutlineV. Free Body DiagramsVI. Effects of a Force at an Instant in TimeVII. FrictionVIII. Impulse: Force Applied over a Period of TimeIX. Work: Force Applied over a DistanceX. PowerXI. EnergyXII. Work-Energy TheoremXIII. Conservation of EnergyXIV. Energy Conversion during GaitXV. QuizOutline of Current Lecture I. Contact ForcesII. Free Body DiagramsThese 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.III. Effects of a Force at an Instant in TimeIV. Impulse: Force Applied over a Period of TimeV. OutlineVI. Work: Force Applied over a DistanceVII. PowerVIII. EnergyIX. Strain (Elastic Energy)X. Work-Energy TheoremXI. Conservation of EnergyXII. Energy Conversion during GaitXIII. Vectors and ScalarsXIV. Position, Displacement, DistanceXV. Velocity and AccelerationXVI. Types of AnglesXVII. Angular and Linear PositionXVIII. Angular and Linear VelocityXIX. Tangential AccelerationXX. Centripetal (Radial) AccelerationXXI. QuizCurrent LectureI. Contact Forcesa. Ground Reaction Force (GRF)i. Force exerted by the ground on a body in contact with itb. Joint Reaction Forcei. Force experienced at a jointc. Inertial Forcei. Force opposite in direction to an accelerating force acting on a bodyd. Muscle Forcei. Force when muscle fibers generate tensione. Elastic Forcei. The tendency of solid materials to return to their original shape after being deformedf. Friction Forcei. The force acting parallel to the interface of two contacting surfaces duringmotion or impending motionII. Free Body Diagramsa. Called a force diagrami. To analyze the forces (linear) and moments (angular) acting on a bodyii. Displays magnitude and direction of forcesIII. Effects of a Force at an Instant in Timea.IV. Impulse: Force Applied over a Period of Timea. An object with momentum can be stopped if a force is applied against it for a given amount of timeb. Force applied over a period of time: impulse = change in momentumc. Impulse is a vector quantity, the direction is the same as the direction of the forced. Symbolized as Ie. Units = kgm/s or NsV. Outlinea. Workb. Powerc. Energyd. Work-Energy Theoreme. Conservation of EnergyVI. Work: Force Applied over a Distancea. Work = force x distanceb. The scientific definition of work is: using force to move an object a distance (when both the force and the motion of the object are in the same direction)c. W = f x cos(theta) x s i. F = applied forceii. S = displacementiii. Theta = angle between the force vector and line of displacement (recall cos(0) = 1)d. Units of work are Joules (1 J = 1 Nm)e. Work is a scalar quantityf. Work is not a function of timeVII. Powera. Power is the rate at which work is doneb. Power = work/time c. Power = force x velocityd. Units of power are Watts (W = J/s)e. Power is a scalar quantityVIII. Energya. Energy is the capacity of a physical system to perform workb. Kinetic Energy (KE) results from motionc. Potential Energy (PR) results from position in gravitational fieldd. Units of energy are Joules (1 J = 1 Nm)e. Energy is a scalar quantityIX. Strain (Elastic Energy)a. Strain (elastic) energy (SE) is the capacity to do work due to deformation of a bodyX. Work-Energy Theorema. The work done by a resultant force is equal to the change in energy that it producesb. This is assuming that no work is done to deform the system (i.e., no strain energyis stored)c. This also assumes that no work is done to increase rotational kinetic energyXI. Conservation of Energya. The total energy of a closed system is constant since energy does not enter or leave a closed systemb. This only occurs in human movement when the object is a projectile and we neglect air resistancei. TE = PE + KEc. Note that gravity does not change the total energy of the system XII. Energy Conversion during Gaita. Walking and running are characterized by energy conversionsi. Walking1. Kinetic-potential energy conversionii. Running1. Kinetic and potential energy are converted to elastic, and vice-versaXIII. Vectors and Scalarsa. Scalarsi. Can be described by magnitudeii. E.g., mass, distance, speed, volumeb. Vectorsi. Have both magnitude and direction ii. E.g., velocity, force, accelerationiii. Vectors are represented by arrowsXIV. Position, Displacement, Distancea. Position WHERE?i. Location in space relative to some reference pointii. Linear and angular position (s, theta)b. Displacement & Distance HOW FAR?i. Displacement1. Final change in position 2. Vector quantityii. Distance1. Sum of all changes in position2. Scalar quantityXV. Velocity and Accelerationa. Velocity HOW FAST?i. Vector quantityb. Acceleration HOW QUICKLY IS VELOCITY CHANGINGi. Vector quantityii. Insight into forces/torquesXVI. Types of Anglesa. Absolute Anglesi. An absolute angle is measured from an external frame of referenceb. Relative Anglesi. A relative angle is the angle formed between two limb segmentsc. Joint Anglesi. Anatomical position is zero degreesd. Hip Anglei. Positive angle for flexion ii. Negative angle for extensione. Knee Anglei. Generally always positiveii. Negative angle indicates hyperextensionf. Ankle Anglei. The 90 degree is added to make the normal ankle angle (when standing) equal to 0 degreesii. Positive angle for dorsiflexioniii. Negative angle for plantar flexionXVII. Angular and Linear Positiona. The linear displacement can be determined when the length of the segment (radius) and the angular displacement are known i. r = distance from axis of rotation (radius)ii. theta = angular displacement (here, in degrees)XVIII. Angular and Linear Velocitya. The linear velocity can be determined when the length of the segment (radius) and the angular velocity are knowni. r = distance from axis of rotation (radius)ii. omega = angular velocity (here, in degrees)XIX. Tangential Accelerationa. Similarly, tangential accelerationi. r = distance from axis of rotation (radius)ii. alpha = angular acceleration (here, in degrees)XX. Centripetal (radial) Accelerationa. Even at constant angular velocities, the direction of the linear velocity changes when going around a curveb. Since velocity is changing, there must be accelerationc. This acceleration is towards the center of rotationi. Called centripetal acceleration XXI. Quiza. If the static coefficient of friction of a basketball shoe