Sport Biomechanics (SB).docx

Applied Sport Mechanics 2 Chapter 4: Linear Motion in Sport ✓ 2 Chapter 5: Linear Kinetics in Sport ✓ 3 Chapter 6: Angular Motion in Sport ✓ 4 Chapter 7: Angular Kinetics in Sport ✓ 5 Chapter 9: Sport Kinetics 6 Lectures 7 Kinematics 7 Kinetics 7 Kinetics, work & power 8 Sport Mechanical Prin...

Applied Sport Mechanics 2 Chapter 4: Linear Motion in Sport ✓ 2 Chapter 5: Linear Kinetics in Sport ✓ 3 Chapter 6: Angular Motion in Sport ✓ 4 Chapter 7: Angular Kinetics in Sport ✓ 5 Chapter 9: Sport Kinetics 6 Lectures 7 Kinematics 7 Kinetics 7 Kinetics, work & power 8 Sport Mechanical Principles of Common Type of Sports Movements 8 Applied Sport Mechanics Chapter 4: Linear Motion in Sport ✓ Linear motion = constant motion Speed and velocity indicate how fast an object is traveling, but they differ when the traveling is matched to a time: Speed = defined by measuring the length/distance that is moved in a certain time, but it does not determine the direction of the movement. Velocity = change in position divided by time (starting to ending point in one straight line) → to calculate the linear motion, measure the distance and time variables Difference: velocity has a direction (shown as a vector), while speed does not (it only has a magnitude/size) Note: velocity and speed can be the same when the direction of movement is in a straight and consistent line. Also note that if you walk in a circle (in which your starting and ending point are the same), velocity is 0. Acceleration/deceleration = the rate at which the velocity (or speed) changes. A force (= push/pull) is needed to hold an object stationary or make it move. Force vector = the combination of the direction and amount of the applied force Head = the direction of the force Length = the amount of force being applied A force that consist of a vertical and a horizontal force component is influenced by gravity (only the vertical force component) Key factors that influence linear motion: Angle of release Straight up → flight path is a straight line up and down Gravity decelerates the object on the way up and accelerates on the way down < 45° → distance > height > 45° →height > distance Speed of release Higher speed of release → higher apex (highest point of flight path) and further travel Height of release No air resistance: 45° produces the greatest distance for objects projected from ground level < 45° produces the greatest distance when the object is projected from above ground level Interrelated components are; velocity, height and angle of takeoff/release (altering one causes changes in the others) Chapter 5: Linear Kinetics in Sport ✓ Newton’s Laws of motion: Inertia = the ‘desire’ of an object to continue doing what it’s doing (staying still, moving at a certain speed, etc) Greater the mass → more inertia (more resistance to change) Once on the move, objects want to move in a straight line (push/pull → curved pathway) Acceleration F = m x a (mass x acceleration) More body mass → more muscular force is needed (proportional to period in which the force is applied) Weight = the earth’s gravity pulling on the athlete’s body Action-Reaction For every action, there is an equal and opposite reaction If there were no opposite forces, any movement would continue indefinitely Momentum = the quantity of motion that occurs Combination of mass and velocity (so a person with a higher mass doesn’t always generate greater momentum) → M = m x v Impulse = the applied force over a certain period of time. Extending the movement (for example leaning backwards)→ extended time (for applying force) → higher impulse In landing: extending the time in which the body receives/absorbs force from the ground → less force athletes enlarge the area of impact to distribute the force Measure linear kinetics in gait: Running velocity = stride length x stride rate Stride length = distance between 2 following points of initial contact of the same foot Step length = distance between the point of contact of one foot and the other Stride rate = frequency/cadence of leg swings Walking/running stages: Stance phase (foot makes contact with the ground); usually 60% of walking cycle Swing phase (foot is swinging in the air); usually 40% of walking cycle Chapter 6: Angular Motion in Sport ✓ Angular motion = an object/athlete rotates around an axis. Angular velocity = the rate of spin of an athlete/object (measured in degrees per second) Instead of linear velocity that describes the rate of movement in a linear direction, angular velocity describes the rate of movement in an angular direction. Angular velocity depends on speed and length to the turning point (= axis) The further the mass is from the axis, the higher is the speed, even though the velocity is the same if both (body)parts ‘arrive’ at the ending point at the same time. Inertia = the resistance to changing the state of motion ⤷ centripetal force pulls/pushes object toward the axis of rotation → curved/circular pathway Centrifugal force = inertia in disguise (fictitious force) Rotation → interplay between inertia, centripetal force, centrifugal force Rotary inertia = the tendency of all objects/athletes to initially resist rotation, until the turning effect of the torque had been applied against them, and then wanting to continue rotating when a centripetal force makes them follow a circular pathway (Newton’s 1st law) ⤷ depends on amount of mass and distribution of mass More massive →more resistant to changing the state of rotation Distribution of mass = how the mass is positioned relative to its axis of rotation Mass further from the axis → greater radius of gyration → greater rotary inertia (slower spin) Rotary interna of a spinning object is proportional to the square of the radius: Doubling the radius → rotary inertia increases 4fold = 1 → ¼ Halve the radius → rotary inertia decreases 4fold = 1 → 4 Doubling/Halving the mass of the object → doubles/halves its rotary inertia Perfect angular velocity in sport: movement is smooth and effortless. Each segment of velocity (plotted against time) follows a similar curved pattern → angular velocity is 0 at the start and the end of the movement and peaks somewhere in between. Kinetic link principle: Chapter 7: Angular Kinetics in Sport ✓ Angular kinetics = rotation and the forces experienced when rotating. The fundamental principle of angular kinetics = gravity: Higher distance → more time to accelerate on the way down A falling athlete is being accelerated by a velocity of 9.8 m/s2 (g) 1 sec into the fall: 9,8 m/s → 2 sec into the fall: 19.6 m/s → 3 sec into the fall: 29,4 m/s etc…) Balance point = the point at which the weight force is equal on either side (add up all the parts of the object) → this is the center of gravity Doesn’t always lay in the exact middle (for example in humans) because of the density of different substances More body mass in upper body → higher CG, more body mass in lower body → lower CG CG can also shift is you change the body’s position: Shift of CG relates to the amount of mass and the moved distance (→ moving legs causes greater shift in CGM because they have more mass) Angular momentum = the quantity of motion that a rotating object/body possesses mass x (angular) velocity Components: Mass How mass is positioned relative to the axis Rate of rotation/swing Ways to increase angular momentum: Increase mass (not possible in practice) Shift as much mass as fas from axis as possible Increase angular velocity (rate of spin) Principle of conservation of angular momentum = rotary equivalent of Newton’s 1st law of inertia (spinning mass wants to continue spinning as long as it’s not stopped) No large mass to push against (because you’re in the air)→ any muscular action causes an equal and opposite reaction elsewhere in the body For example: you flex your hips and raise your legs, your trunk will lean forward (action-reaction) Chapter 9: Sport Kinetics Fundamental mechanical concepts that are involved in movement: Work: the force an object/athlete has applied over a distance (it moves) Impulse = change in momentum (= change is velocity for equal mass) Work and impulse are related when a resistance is moved over a certain distance Power: the work that had been done over a certain period Energy: how much work can we do Forms of mechanical energy: Kinetic energy Gravitational potential energy Strain energy Rebound: the spring back after hitting/colliding with something Friction: the resistance to movement Lectures Kinematics Kinematics describes everything that is moving. Linear → position velocity Angular (rotations) → position velocity acceleration Linear kinematics Different definitions of quantities: Scalar quantities (point, a number) = speed Vector quantities (arrow) = velocity Difference between speed and velocity: Difference between distance and displacement: Distance = the distance covered to go from point A to point B. Displacement = shortest distance between point A and B. Distance is very high in comparison to the displacement → movement is not efficient (for example when a subject has a wide step during gait/running) Calculating jump height: h = 1/2at2 Angular kinematics Most injuries occur at the point of maximum acceleration (which is when the angle of the joint is almost at a maximum). Kinetics Kinetics describe the causes of motion. Force → linear movement Torque → angular movement Kinetics, work & power Acceleration down Acceleration up Newton’s Laws of motion: 1st law of motion: Inertia = The desire of an object to continue doing whatever it’s doing (motionless → remain motionless, slowly moving → continue slowly moving, moving fast → continue moving fast) Inertia = the resistance to change movement 2nd law of motion: Acceleration = To change an object’s state of motion, a force is needed to accelerate it Force = m x a (mass x acceleration) Momentum = the quantity of motion ⤷ M = m x v (mass x velocity) → heavier object = more momentum 3th law of motion: Action-Reaction = For every action, there is an equal and opposite reaction Ground reaction force (GRF) is proportionate to acceleration (if the acceleration goes down, the GRF is smaller (than the force of gravity), if the acceleration goes up, the GRF is bigger). ! Activity of a muscle group (EMG) does not mean the muscle is loaded. Sport Mechanical Principles of Common Type of Sports Movements The load is lower when you have more time to reach a certain force. Momentum at stationary point = 0. Only perpendicular forces will produce movement in a torque.