KNS 422 Linear Kinetics
What are Newtons 3 laws and their respective definitions?
1: Inertia: body will maintain in a state of rest or constant velocity unless acted upon by an external force(F=ma) 2: Acceleration: force applied to a body causes an acceleration of that body proportional to the force in the direction of the force, inversely proportional to the body's mass (a=F/m) 3: Reaction: For every force, there is an equal and opposite force
What is the relationship between the moment arm of a muscle and its attachment angle?
Although muscles produce linear forces, motions at joints are all rotary. The moment arm or mechanical advantage of the muscle is about the join's center or rotation. Mechanically, the is the distance from the muscles line of action to the joint's center of rotation.
What is impulse or momentum? what is the relationship btwn them? How is this principle between impulse and moment derived?
An impulse is an external force applied over a period of time -> I=F*t Momentum is at a specific point in time An external impulse will cause momentum to change(F*t=m(vf)-m(vi))
What is the biomechanical concept related to explosiveness in sports?
Explosiveness is related to v= r* omega v= linear vel r=meters omega=ang vel One has to be physically explosive to increase angular velocity, which is achieved through increased body coordination
Can you provide examples in sports where the inc/dec friction have on sport performance and injury prevention
Greater Coeff of Friction= greater trip hazard Smaller COF= greater slip hazard ACL injuries and "turf toe" occur because of too much friction due to turf Ice skaters want a lesser COF(Fresh ice) to skate more easily whereas a golfer wears a glove to increase COF and have a better grip on the handle ***Valiant suggest 0.8 COF PROVIDES SUFFICIENT TRACTION FOR ATHLETIC MOVEMENTS and any greater COF may be unsafe
Why is the kinetic friction smaller than the static friction?
Static friction is the friction that keeps an object in place. This friction must be overcome by energy to move the object. ->Because of a combo of surface irregularities and electral charges between the obj and surface, the energy required to initially move the static object is greater than the energy required to keep it in motion -> Because it takes more energy to move the static obj, physicists say that static friction is greater than kinetic --> The smoother the surface the smaller the diff between the amount of static and kinetic frictions
What are the 2 common units for GRF in biomechanics?
Newton/kg -> Body weights
How does one determine the coefficient of friction?
The Coefficient of friction is defined as the ratio of force of friction to the normal force u= F/N
What is potential energy
Potential energy is the energy possessed by a body by virtue of its position relative to others, stresses within itself, electric charge, and other factors.
What is power?
Power is the rate of doing work. It is the amount of energy consumed per unit time. Having no direction, it is a scalar quantity In the SI system, the unit of power is the joule per second(J/s) known as the WATT
****What are the characteristics of vertical and horizontal ground reaction force(GRF) curves in walking and running? What about the GRF curve in vertical jumping and landing from the jump?
Running A/P view is very similar to walking just shorter in duration(.25sec vs .70 sec)
****How can you measure/estimate one's vertical jump height? How can you estimate the jump height from the vertical GRF curve? Can you do so using the horiz GRF curve and why?
h= (V^2)/2g Vf^2= Vi^2 +2ad PE= -mgh
What is the conversion factor between pounds and newtons?
Multiply pounds by 4.4475 to get Newtons 1kg= 9.81 N
Can you use the discussed mechanical principles to describe the key performance related characteristics in a tennis serve
Increase angular momentum = serve speed -> The faster the racquet head accelerates and the more time it is given to accelerate, the greater the force and impulse on the ball. -> Serve windup the COG should be shifted toward the backleg to increase the distance of the moment arm and distance of racquet swing. Forces leg and back muscles to contract and store energy, increasing PE -> Rotation of the racquet arm, torso, and legs is significant to power. This produces a greater torque force and increases the angular acceleration and momentum of the racquet which inc power -> Tossing the ball further in front of the body shifts the COG forward in the follow through is effective. This allows the server to xfer energy and momentum from the mass into the serve which inc ball speed. -> End phase of kinetic chain is quite effective(Wrist flick) The wrist flick is the release of strain energy, and due to this flick it creates more power and vel on the ball.
What is kinetic energy?
Kinetic energy is the energy possessed by an object due to its motion. An object must be moving to possess kinetic energy. The amount of kinetic energy possessed by a moving obj is dependent on mass and speed
Example of Newtons 3rd law in sports
Law of Reaction(When 1 body exerts a force on a second body, the 2nd body exerts a reaction force that is equal in magnitude and opposite in direction) Ex: Shooting a basketball and it hits the backboard -> When it hits the backboard it bounces back. This is because the backboard exerts a reaction force that is equal in magnitude and opposite direction to the force of the basketball
Example of Newtons 2nd law in sports
Law of acceleration(force applied to body causes acceleration of body that is proportional to the force, in the direction of the force and inversely proportional to the bodys mass) Ex: lifting a barbell during deadlift ->As you extend your legs through the lift, the force of this motion allows the barbell to acceleration proportionately to the force being applied in a positive direction
Example of Newtons 1st law in sports
Law of inertia(tendency to resist change in motion) Ex: ice skating -> You have to stop yourself with the blades of your skate or else you will hit the rink
What are the properties of force?
Magnitude: amount of force exerted Force line of action: straight line passing through the point of application and is parallel to the direction of the force, muscle attachments, moment arm Point of application: where the force is applied Direction: the way the force is applied along the action line
What is the condition for conservation of mechanical energy?
Mechanical energy is the sum of the potential and kinetic energies in a system. The principle of conservation of mechanical energy states that the sum of the potential and kinetic energies remains constant as long as the only forces acting are conservative forces
Can you use the discussed mechanical principles to describe the key performance related characteristics in a Soccer Kick
The approach: Common for players to ensure they have 2-4 step arc run up w/ 45 deg starting angle. Power in the kick is generated during this phase w/ players increasing momentum and the xfer of that end on the length of the final step into planting the foot.(Greater the step the greater the power xferred onto the ball as a produce from the velocity produced by the leg) Contact Phase: The event in which players have placed their plant foot and are beginning forward motion of kicking leg onto the impact on the ball. During this, players have support leg flexion at foot-ground contact of 26 deg at the knee. Increases to 42 deg when the kicking leg begins to contact the ball. This motion in the support leg is required for the deceleration of body movement and allows continued velocity of the kicking leg which is free from deceleration due to the angle of the hip and pelvis to allow the swing through Follow through phase: Phase when players make contact w/ ball and kicking leg follows through. The follow through phase has a decrease in the distance between kicking leg and opposite elbow. THis puts forth the motion that the follow through phase relies on the kicking foot being above the hip and having the landing on the kicking leg. BIOMECHANICAL PRINCIPLES THAT INFLUENCE A SOCCER PLAYERS ABILITY TO ACHIEVE MAX VELOCITY INSTEP KICK ---> Angular vel of lower limbs, Coeff of restitution, and Ground Reaction Force
What is the condition for conservation of momentum?
The law of momentum conservation states that for a collision occurring between obj 1 and obj 2 in an isolated system, the total momentum of the 2 objs before the collision is equal to the total momentum of the objs after the collision FRICTION MUST=0 FOR THIS TO APPLY
Can you use the discussed mechanical principles to describe the key performance related characteristics in a Volleyball Spike
The running approach to the spike is important to give the player maximum momentum for the height of jump. -> The components that relate directly to momentum are the velocity of approach and the mass of the player. During the approach, body momentum builds up KE --> The goal is to xfer this energy through keeping the body moving -> The relationship btwn KE and Newtons 3rd law is what created a greater jump height. The power of the jump comes from the very force generated from the foot plant and leg push off, WHile the xfer of momentum is due to the direction of the plant foot and use of the arm swing. AKA SUMMATION OF FORCES -> The arm swing is one of the most important factors that contributes to spike jump height. The arm is initially hyperextended to prepare for the best forward position when they are swung upward, forward and downward. --> When the arms are in upward accel, they push against the inferior parts of the body to inc downward force that acts upon the floor. Therefore, generating greater amounts of vert momentum will inc the height of COM at take off. -> The arm momentum and position, along w/ trunk rotation and flexion also play a part in the ball velocity.
How do you determine the coefficient of elasticity of a soccer ball?
Under a direct impact, one can calculate the coeff of restitution. This is the ratio of difference of the velocities before and after impact e= (V1-V2)/(u1-u2) The coeff of a soccerball is roughly .76 because for most impacts 0<e<1
What is the work and energy relationship/principle
Whenever a force is applied to an object, causing the object to move, work is done by the force. If a force is applied but the object doesnt move, no work is done If a force is applied and the object moves a distance(d) in a direction other than the direction of the force, less work is done than if the object moves in the direction of the force.
What is work?
Work is equal to Force(N) times distance(meters)
