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This 11 page Study Guide was uploaded by Logan Harker on Friday February 5, 2016. The Study Guide belongs to PE 3060 at Southern Utah University taught by Dr. Thomas in Winter 2016. Since its upload, it has received 30 views. For similar materials see Biomechanics in Physical Education at Southern Utah University.
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Date Created: 02/05/16
Vocab INTRODUCTION TO BIOMECHANICS Biomechanics: The study of forces and their effects on living systems or organism. You study biomechanics so you can help someone (1) improve their performance or (2) reduce their risk of injury. 1) Improve Performance a) Technique improvement b) Equipment improvement c) Training improvement 2) Decrease Injury Mechanopathology: The mechanics that result in an injury Pathomechanics: The mechanics that are a result of an injury Environment and other external factors can also be potentially injurious a) Techniques to Reduce Injury (i.e. changing landing strategies) b) Equipment designs to reduce injury (football helmets) Principles Governing Biomechanics Mechanics is the analysis of forces and their effects, to study the anatomical and functional aspects of living organisms. Mechanics Dynamics: deals with things that are moving. in accelerated motion (speed up, slow down, change direction). all forces are unbalanced. Kinematics: study of motion. size, sequencing, and timing of movements. Kinetics: study of causes of that motion. force. Statics: deals with loads that are not movingobjects at rest or at a constant velocity. all forces acting on the body are balanced (equilibrium). Exhibit none or constant motion. Loads Response to loads All motion, including motions of the human body and its parts, is the result of the application of forces and is subject to the laws and principles that govern force and motion. LANGUAGE OF BIOMECHANICS UNITS OF MEASURE Quantity Symbol SI Unit Abbreviation Other SI Units English Units for SI Unit Time t second s millisecond minute, hour, day, week, year Length l meter m millimeter, inch, foot, yard, centimeter, kilometer mile Mass m kilogram kg gram slug Temperature K Kelvin K Fahrenheit, Celsius, Rankine KINDS OF MOTION Motion is the act or process of changing place or position with respect to some reference object. Relative Motion Depends on reference, global or local. ● A body is an object of analysis – it could be a whole person, a part of a person, or an inanimate object. ● A system is an object of analysis that is made up of two more bodies. ● A frame of reference is the perspective from which the movement is described. ● The origin is the place where the frame of reference begins. ● Direction is pointing toward something determined by its orientation. Positive direction runs from left to right, down to up, and forward, and negative direction runs right to left, up to down, and backward. ● Orientation is a particular reference line. ● An axis is a straight line running through the origin specifying a direction from the origin. ● The sagittal plane – an anteriorposterior plane formed by the x and yaxes that divides medially/laterally or right/left ● The transverse plane – a horizontal plane formed by the x and zaxes that divides the body superiorly/inferiorly. ● The frontal plane – a sidetoside plane formed by the y and zaxes that divides the body anteriorly/posteriorly. ● Mediolateral axis (FRONTAL) is perpendicular to the sagittal plane. ● Anterioposterior axis (SAGITTAL) is perpendicular to the frontal plane. ● Longtitudinal axis (VERTICAL) is perpendicular to the transverse plane. Relative motion is defined in relation to the specific reference object or point. ex. Two joggers at same speed look at rest relative to eachother even though they are moving relative to the earth. A faster jogger would be jogging 2km/hr faster to the slower jogger and 10km/hr to the earth. Causes of Motion Each cause of motion is a form of force. Inertia: A resistance to change in motion, specifically a resistance to change in a body's velocity. Kinds of Motion Linear (translatory) movement: object is translated as a whole from one location to another All points are moving the same distance, the same direction, at the same time Rectilinear: straightline progression of an object as a whole. uniform rate of speed. Curvilinear: curved translatory movement/curved pathway. Angular (Rotary) Movement Object acting as a radius moves about a fixed point (axis of rotation) Movements of most human body segments (ex. cyclist) Other Movement Patterns A combination of rotary and translatory movement General motion: combination of rotary and translatory movement Relationship between linear and angular motion Kinds of Motion Experienced by the Body Mostly angular Sometimes translatory Rectilinear is acted on by the forces of gravity Rotary Curvilinear Reciprocating (swinging) Factors that determine type of motion Depends on the kind of motion permitted in that particular kind of object Lever: angular Freely movable: translatory or rotary Depends on center of gravity, pathways or movement available to object, and presence/absence of additional external factors that modify motion Factors modifying motion Friction Air resistance Water resistance Help or Hindrance Internal factors: anatomical factorstension and joint capsules LINEAR KINEMATICS Kinematics: The study of motion without considering what is causing the motion. Relates to change in position, velocity, and acceleration Linear motiontranslation Scalar: A quantity that only has magnitude Vector: A quantity that has both a magnitude and spatial direction Frames of Reference 1. What is moving? 2. What is it moving in relation to? Quantities of Linear Kinematics Position: Location in a reference frame. vector. Location on axis and which side of origin (+,) Displacement: A change in position. vector. Distance: How far a body has traveled. scalar. Speed and Velocity Rate: How quickly a value is increasing or decreasing with time. Speed: How fast a body is moving Velocity: How fast something is moving in a particular direction Instantaneous: The value of a quantity at a particular moment in time. Use smaller increments of time. Instead of velocity position being final and initial, you use two close data points that occurred during the entire displacement. Obtain more detailed information this way Could find resultant instantaneous velocity, or the components x and y that make up the displacement Acceleration: How rapidly something is changing velocity (speeding up or slowing down). vector. Could also be a change in direction. Constant Acceleration: velocity changing by a constant amount each second +: speeding up positive, slowing down negative : slowing down positive, speeding up negative EXAMPLE OF LINEAR KINEMATICS: ONE DIRECTION 100m dash Position vs. Time: points are position at that particular moment, slope is velocity (steeper slope greater velocity) Velocity vs. Time: points show the velocity at that particular moment, slope is acceleration Acceleration vs. Time Why someone won the race: ● Top speed (instantaneous speed) ● The time it takes them to get to the top speed (acceleration) ● The duration they hold their top speed ● The difference between the top speed and final speed EXAMPLE OF LINEAR KINEMATICS: TWO DIRECTIONS Shuttle Run The axis The magnitude of the change in position The direction of the change in position Can have a net displacement of 0 if the starting position is the same as the final even if distance was covered The sign of the velocity is always in the direction of the displacement. If the total displacement is zero then the average velocity is also zero Average velocity over give displacement. In reality velocity is constantly changing throughout run A negative velocity does not mean a body is slowing down, only that it is moving with a certain speed in a negative direction. Zero velocity on a curve indicates that either a body is not moving, or it changed direction. A change from a positive direction to a negative one (and vice versa) will always require the velocity to be zero during the transition – however brief. Acceleration represents a change in the magnitude of velocity, the direction of the velocity vector, or both. Whenever the velocity starts at zero and ends at zero, the average acceleration must be zero. Small time periods=approx. instantaneous measurement Peak velocity=zero acceleration Asymmetric Acceleration Profiles Projectile: An object in the air that is only subject to the force of gravity and wind resistance after it leaves the ground. LINEAR KINEMATICS IN TWO DIMENSIONS Planes: A smooth flat space defined by two axes Resultants and Components Resultant: A vector that is equivalent to the combined effect of two or more vectors. Components: Parts of a resultant vector, two or more vectors that are acting in different directions. Net Values Net: The total value after summing all of the individual values. A warning here: Do not think that you need to know the resultant and angle! It is only the velocity in the x direction that determines how long it takes her to go 50 meters in the x direction. The only thing the y velocity affects is how far she goes in the y direction in the same amount of time. PROJECTILE MOTION Trajectory: The path of a projectile. Influenced by gravity Force of Gravity: The mutual attraction between the earth and an object. The force is always directed vertically downward toward the center of the earth, thus, causing a constant acceleration of 9.82 m/s2 The Influence of Gravity ● The force of gravity produces a constant acceleration of 9.81 2 on bodies near the surface of the earth. ● The pattern of change in the vertical velocity of a projectile is symmetrical about the apex. ○ The vertical velocity at the apex is zero. ● Vertical velocity decreases as the ball rises and increases as the ball falls due to the influence of gravitational force. Vertical velocity will decrease as the object travels upward; and increase as the object travels downward. Horizontal velocity will not change. At the top of the path, or the apex, vertical velocity is zero. An object taking off at the same level that it lands will have the same angle at takeoff as at landing, and the resultant velocity will be the same at takeoff as landing. Replacing a with ag and rearranging the preceding equation, you get: Change in position due to gravity: Notice that gravity will alter the path of the projectile by The magnitude of the alteration is not constant: As time increases, there will be a greater change in the trajectory of the projectile. This relation is not a linear one: Doubling the time will lead to a fourfold change in position because of the time term in the equation is squared. Relative height of TakeOff/Release Relative Height: The difference between the vertical position at takeoff and the vertical position at landing. Apex: The highest point of a trajectory. Increasing the height of takeoff/release will increase the time in flight. Increasing the height of takeoff/release will increase the horizontal displacement. Angle at TakeOff/Release Trig Parabola: A type of plane curve. The horizontal velocity is constant, but the vertical velocity is not; it starts at the takeoff velocity and decreases at a constant rate of 9.81 m/2. At the apex, the vertical velocity is zero. ■ Vertical velocity will decrease as the object travels upward and increase as the object travels downward. ○ Horizontal velocity will not change. ○ At the top of the path, or the apex, vertical velocity is zero. ● The parabola is symmetric about the apex. ○ An object taking off at the same level that it lands will have the same angle at takeoff as at landing, and the resultant velocity will be the same at takeoff as landing. Velocity at TakeOff/Release Resultant velocity: divided into vertical and horizontal components How far did the object travel? affected by horizontal velocity and time in air also by velocity of takeoff and the angle of takeoff Ultimately, the range of a projectile depends on three things: 1. The maximal velocity at takeoff 2. The optimal angle of takeoff 3. An increased relative height How high did the object travel? How long in flight vf, is the final vertical velocity is the vertical velocity at apex, which is zero. How fast at release *Most influential factor is velocity* ANGULAR KINEMATICS Angle: The amount of turn between two straight lines that have a common end point (the vertex) Angular position refers to the orientation of a line with another line or plane. Absolute angular position: the angular orientation of a body segment with respect to a fixed line of reference (e.g., vertical or horizontal). Relative angular position: the angle between two moveable lines and/or planes. Angular distance: sum of all angular changes undergone a rotating body. Angular displacement: The change in orientation of a rigid body in reference to some axis. Angular speed: How fast a body is rotating. Angular velocity: How fast a body is rotating in a particular direction. Angular acceleration: How quickly a body is speeding up or slowing down its rotation in a particular direction. Angular acceleration may be positive, negative, or zero. ● Zero = angular velocity is constant ● Positive = increasing angular velocity in the positive direction OR decreasing angular velocity in the negative direction. ● Negative = decreasing velocity in the positive direction OR increasing angular velocity in the negative direction. RELATIONSHIP BETWEEN LINEAR AND ANGULAR MOTION Angular displacement in radians where, = arc length, Δθ = angle measured in radians, and r = radius. ***WARNING** must be expressed in the units of radians for this expression to be valid. The relationship between linear displacement and radius is easily seen in this figure. From this, the following relationship can be established: where r = radius and d = displacement (or chord length). Deriving Relationship L=A Dividing both sides by the time it takes to rotate through the displacement gives us At an instant in time, this relationship becomes Tangential Acceleration (needs to be in radians) Radial Acceleration
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