KIN 365 test #3 STUDY GUIDE
KIN 365 test #3 STUDY GUIDE KIN 365
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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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