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KIN 365 test #3 STUDY GUIDE

by: Allie Newman

KIN 365 test #3 STUDY GUIDE KIN 365

Allie Newman
GPA 4.0

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all of test #3 notes
Applied Biomechanics
Mark Richardson
Study Guide
50 ?




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This 20 page Study Guide was uploaded by Allie Newman on Wednesday November 4, 2015. The Study Guide belongs to KIN 365 at University of Alabama - Tuscaloosa taught by Mark Richardson in Fall 2015. Since its upload, it has received 56 views. For similar materials see Applied Biomechanics in Kinesiology at University of Alabama - Tuscaloosa.


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Date Created: 11/04/15
KIN 365 Class Notes for Test #3!! 10-14-15 Center of Gravity:  Definition  A location whereby all of the mass of a body or object is evenly distributed around  Could be very center of object, but a lot of times it is not o Often located outside the body or object  No tendency to move, no rotation Work:  Work = Force x Distance  1 Nm = 1 Joule Internal and External Forces: Only an external force can cause a change in motion! o Earth pushing back  ground reaction force Quad is internal force … earth pushes back (external force) exactly as hard and exactly opposite in direction o Changes in every situation, you have to decide when internal and when external! o On earth, there is always opposing forces 4 Properties of a force: o Magnitude  Little force or big force?  representation of amount of force  ½ force means ½ magnitude o Direction  Force is exerted in a certain direction o Point of application  When hand touches football to be thrown, when a bat hits the ball, etc. o Line of action  Goes in both directions!  where object is headed and opposite (where coming from) Reaction Forces:  The environment delivers a reaction force in response to the force body segments exert on the environment  Newton’s Third Law of Motion: o For every force applied by one body on a second, the second body applies an equal and oppositely directed force on the first  “For every action, there is an equal and opposite reaction” 10-16-15 Class Notes!!! Friction Force: o Friction is the force created between two contacting surfaces that tend to rub or slide past each other o Friction Force = Normal force x Coefficient of Friction o Motion is impaired o Sanding wood: need a lot of friction: COARSE piece of sandpaper and press down HARD  The ROUGHER the surface  the higher coefficient of friction  Normal force  how hard you press o Zamboni on Ice Rink: decreases friction Centripetal and Centrifugal Forces: o Centripetal Force:  Responsible for continually forcing the rotation object to follow the circular path o Centrifugal Force:  Equal and opposite reaction force o Centripetal Force needed = Mass x (Speed) / radius of circle  Wider the turn  decreases the centripetal force needed  Narrower the turn  increases the centripetal force needed ~ Horizontal component of the Ground Reaction Force = Centripetal Force~ ~ On a wet rainy day, you want to make a SLOW, WIDE turn~ Elastic Force: o How readily will an object reform after being deformed? o Coefficient of Elasticity (e) o e = (entire square root of) height of rebound / height of drop o Something does NOT bounce higher than it is dropped (typically) o When it hits the ground, some of the energy goes off as heat Internal and External Forces: o The Effect of Internal Forces: ***he didn’t talk about these at all but they were on his paper** o The Effect of External Forces: Motive and Resistive Forces: o Motive = Force that CAUSES the motion o Resistive = Causes the OPPOSITE motion o Example: concentric bicep curls… Bicep = motive, Weight = resistive o BUT with eccentric bicep curls… Bicep = resistive, Weight = motive Power:  Power = (F x D)/T  Power = F x (D/T)  distance/time = velocity  Power = F x V  Power = Force x Speed of force application Energy: the ability to do work  Many forms… o Nuclear o Heat o Chemical o Electrical o MECHANICAL 1) Kinetic = energy of motion  KE = ½ mv  (mass)(velocity) 2) Gravitation potential energy  PE = w x h  (weight)(height above the ground) 3) Elastic potential energy: [springs are a great example]  Ability of a body or object to do work while it recoils (or reforms) after being stretched or compressed  Potential turns into Kinetic 10-19-15 Class Notes!!! Vector = a tool  Vector quantities = magnitude and direction o Examples  force, velocity, weight, etc.  Scalar quantities = magnitude only o Examples  mass, volume, and area Force Diagrams and Vectors: Vector Composition: o More than one external force applied to a system  Net effect (what is the result?) = determined by vector composition  The length of the vector (in the pic, the arrow) equals the magnitude of the force  Point of application, where the force is applied, where the vector starts, moving in a certain direction (direction the force is moving towards)  1 cm = 3 Newton’s  Represents the weight of the baseball Vector composition: o When you go from 2 to 1 o You want to know the result (resultant vector)  Where that ball is going and how much force it has o Where they cross is where you draw your vector!  Result of gravity and result of crosswind (result of two effects)  From two vectors into one vector Another Vector Composition Example:  The net effect of two non-perpendicular forces applied to a soccer ball Another Vector Composition Example:  These two forces are co-linear: o Forces that are acting along the same line of action o Subtract smaller from the larger force Vector Resolution:  The reverse of the process of vector composition o Taking a vector and breaking it into vertical and horizontal components (or other components) o Going from 1 to 2 - (going from one force, to two forces) o Opposite of vector composition  The arrow in the above picture is a force vector representing the force of the bicep  Direction of the force = direction of force that bicep is pulling up  Length of arrow is magnitude of the force  Insertion of bicep = point of application (of force)  where all three arrows start (same point)  Rotary component will always be 90 degrees from the stabilizing component (see above pic for visual)  Rotary component has less magnitude than the force vector o (See how the force vector arrow is thicker than the rotary component arrow in above pic) 10-21-15 Vector Resolution:  The reverse of the process of vector composition o Taking a vector and breaking it into vertical and horizontal components (or other components)  It used to visualize the effects of muscle pull on the bone Rotary component Stabilizing component Torque:  When an external force acts on a system which is restricted to moving around an axis, the result is a rotary motion  Eccentric Force  off axis o Also must not pass through the axis  Force Arm  shortest distance from the axis of rotation to the line of action of the force o It is the only perpendicular (90 degrees) distance from the axis of rotation to the line of action of the force  Torque  turning effect on body produced by force (force times force arm) o The worlds strongest people have short force arm (what it means to be human) Properties of Torques:  Magnitude  Torque = Force times (perpendicular distance/force arm)  Direction  clockwise (-) and counterclockwise (+)  Point of Application  of the force  Line of Action  of the force Calculating Torque:  Torque = force times force arm  Torque is expressed in Newton meters (Nm)  Remember the distance from the axis must be perpendicular to the line of the force o When you do a bicep curl, the force arm changes through a full range of motion o That is why you feel strong at some joint angles, and not as strong at others  Can you ever have simultaneous linear and rotary (restricted to a fixed axis) motion? o Yes you can!!  Ball has rotation = rotary motion and also has certain direction of movement = linear 10-23-15 Biomechanics of the Musculoskeletal System:  The mechanical aspects of the bone-muscle arrangements results in producing segmental movements o These are accomplished by machinelike mechanisms  Four Functions of a Machine: o Balance two or more forces o To provide an advantage in force o To provide an advantage in range of linear motion and speed of movement o To change the effective direction of the applied motive force  Example  lat pull downs  Three Machine-Like Structures Used by the Body Include: o The lever o The wheel-axle o The pulley  Example  lat pull downs  Lever-Like Arrangements: o A lever system consists of an axis of rotation around which a rigid lever moves  Forces and torques applied to bones o Force vector representing the force of the gastrocnemius  “Gastrocnemius creates this amount of torque” – rotate the boney lever o The arrow represents how much force (magnitude) o Force line is always either the perpendicular line, or the shortest line  Which force produces more torque? (F1 or F2) o F1 has the longer force arm, therefore will produce more torque  (F1 and F2 have same amount of force, just different force arm)  It’s not all about force, but also the angle in which the muscle pulls at 10-26-15 Effect of net torque on a bone-lever system: o Remember  motive and resistive torques  Motive torque is the torque that causes the motion  Resistive torque is the torque that produces the opposite o To determine whether a segment will move:  The sum of the torques in each direction must be determined  Whichever one is greater, that is the motive torque, in which direction it will move  Net Torque = Large minus small Static Tension; isometric contraction  Net torque; concentric contraction  Eccentric Contraction Add up the torques, whichever one is bigger, that is the direction in which it will move Force vector representing the amount of force of the bicep:  our muscles are strong, but exertion of that strength is not easy (we have a disadvantage as humans)  force arm changes throughout the full range of motion!! (longest at 90 degree angle) 10-28-15  Analysis of the musculoskeletal lever system  Rotary and joint-stabilizing components  Evaluating several joint positions ▯ ▯ What is different at the 3 different joint positions?  Rotary component vs. stabilizing component o 1 vector  2 (vector resolution) o stabilizing is longer than rotary o more force is shoving knee together (stabilizing) than moving leg (only rotary component causes movement) st  1 joint position: o rotary and stabilizing components  2nd joint position: o at 90 degree angle of pull, all the force causes motion o all rotary component ▯ rd  3 joint position: o dislocating and rotary A comparison of 3 elbow flexors: ▯ ▯  Rotary component of brachioradialis is very small ▯  Biceps brachii has the best biomechanical advantage because it has the greatest rotary component ▯ ▯ Mechanical advantages:  The muscles of the body are at a mechanical disadvantage in force  Muscles’ lines of action run very close to the axes of rotation for the joint movements o Thus, they have small force arms o Biceps attachment are so close to line of action (child sitting too close to the middle of the teeter totter)  Mechanical advantage = Resistive force/ motive force  Mechanical advantage = motive force arm/ resistive force arm  What good is it to have strong muscles?? If we are at a mechanical disadvantage? 11-2-15 11-2-15  We do have a mechanical advantage in range of motion and speed of movement!!! o But, we are at a mechanical disadvantage in force  The musculoskeletal level system does have a mechanical advantage when it comes to: o Range of motion o Speed of movement  Mechanical Advantage  motive force arm / resistive force arm o Mechanical advantage means little input, for a large output ▯  Dorsiflex (moving the foot upwards, pointing towards the sky)  Arrows pointing down in pic represent the force vector which represents the weight  Motive force vs. resistive force o Which one moved further?  resistive force moves further! (larger distance)  This is an advantage in range of motion (we got it to move far, and we did not have to move very far  large output, for little input) o Did they move in the same amount of time?  Yes, both forces moved different distances in the same amount of time o Which one was going faster?  Resistive force moves faster (because it moved further/more distance in the same amount of time that motive force was)  This is an advantage in speed of movement o We can move things fast and far, but it better be light (must not weigh much, not be heavy) o Resistive gets longer force arm (over motive force) o Axis is in between the motive and resistive forces 3 Classes of Levers:  Levers are classified according to: o The relative positions of the axis o The motive force o The resistive force First Class Levers: o The axis is located between the motive force and the resistive force o First class levers are rare in the human body o Examples:  Teeter totter  Concentric contraction (pulling arm up, curling arm)  Triceps  Posterior calf muscles Second Class Levers: o When the rotary component of the resistive force is located between the rotary component of the motive force and the axis  “When the resistive force is located between the motive force and the axis” o During an eccentric contraction (of a typical joint), the resistive force is in between the axis and the motive force  this is a second class lever**  Third Class Levers: o When the rotary component of the motive force is located between the axis and the rotary component of the resistive force  When the motive force is located between the axis and the resistive force o Most musculoskeletal lever arrangements are of the third class when the muscle is the motive force Wheel and Axle-Like Arrangements:  Mechanical Advantage (in force when the motive force is applied to the wheel) = o radius of the wheel / radius of the axle  Mechanical Advantage = force on the axle / force on the wheel  Examples  can openers, automobiles, etc. 11-4-15 Pulley-Like Arrangements:  Example  medial and lateral malleolus Pulleys can change the effective direction of the applied motive force o You pull down, and the weight goes up o Do we use pulleys as a mechanical advantage in force?  no!  What about other machines? Levers? Axles?  no!  Human Body = built for speed and range of motion  We use pulleys NOT to gain mechanical advantage in force o We use it to change the effect direction of the applied motive force Review: Rotary Component:  Only component that is actually causing movement  It is always at a 90 degree angle o 90 degree angle means largest force arm Centripetal Force:  Horizontal component of ground reaction force  Inward directive force o The force that keeps something rotating Centrifugal Force:  Outward directive force o Example  when turning in car, and your body falls to the side Example  Riding Bike on Wet Rainy Day  Had to go slower, because you have less centripetal force o Because it was wet, so you can’t apply as much force on the earth, and therefore the ground can’t push back as much either o Must slow down, and make a big wide turn Force Needed = mass x speed squared (^2) / radius of circle Elasticity (e) = square root of (height of rebound / height of drop)  The larger the rebound, the higher the elasticity (i.e. tennis ball will be more elastic than a bowling ball)


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