Chapter Three : Kinetic Concepts of Human Movement Flashcards
Biomechanics
The science of studying living things from a mechanical perspective
What is biomechanics used for?
Using the principles of physics to help develop and refine human movement.
Structure and design of equipment
Movement techniques
Causes of overuse injuries
Improving movement for people with disabilities
Quantitative analysis (biomechanics)
Is based on measurement of kinetic (force) and kinematic (distance,speed,acceleration) variables. ie; Technology Video Gonimetry Optoelectronic Electromyography Accelerometers Light gates Timers Force platforms
Qualitative analysis (biomechanics)
Involves descriptions of the quality of the movement
ie; video analysis
Coaches/teachers/trainers analysis
Optoelectronic analysis
Force definition
A push or a pull acting on an object
How does force affect an object
- Change the shape of the object (stretching, squashing or twisting)
- Move the object (start moving, slowing down, changing direction)
Example of force
The force that is put on a pedal by a cyclist makes it move
When a muscle contracts and pulls on the bone
When a tennis ball hits a racquet the strings change shape temporarily
Force equation
Force = Mass X Acceleration
Unit of force is Newtons (N) which is the amount of force required to accelerate 1kg of mass at 1m/s2
Types of Force
Friction
Drag force ( Air and Water)
Gravitational force
Weight
Friction
A force that acts in the opposite direction to motion when 2 surfaces are in contact with one another
Example of increasing friction
Weightlifter uses magnesium chalk to increase friction between hands and bar
Sports shoes worn in volleyball have rubber on the soles to prevent slipping
Football boots have studs to increase friction between the pitch and the shoe to prevent slipping
Example of decreasing friction
Skiis have a flat surface at the bottom of the ski to decrease friction to allow skiier to slide faster
Ballroom dancers have highly polished shoes to decrease friction to allow them to slide to complete dance moves
Ice rinks are resurfaced to be made flat so that the ice skater can glide across the rink easier
Moving an object across a surface in terms of friction
Applying an increasingly greater force that will overcome the maximum static friction. Friction increases as force is applied so once a force becomes greater than friction an object will begin to move.
Maximum static friction definition
The maximum amount of friction that can be generated between 2 non-moving surfaces.
Drag force definiton
When an object or body moves through air or water it will experience an opposite force slowing the object down.
Factors affecting drag force
Air density
Cross sectional area of the body
Speed of the object
Maximising speed in terms of drag force
Reducing impact of factors other than speed through technique (body position) and clothing
Gravitational force definition
Force of attraction between 2 bodies or objects
Mass definition
Is a measure of the amount of matter an object is made up of. (kg)
Weight definition
Refers to the force exerted on the body by gravity. It is directly proportional to the mass of the body (newtons)
Acceleration due to gravity
9.8m/s
Weight calculation
Weight = Mass X Gravity (kg.m/s2)
Inertia definition
The tendency for a body/object to resist a change in its state of motion
Motion and inertia
Greater mass gives a greater inertia
Greater inertia makes it harder to change its state of motion
Example of inertia
It takes more force to move a 20kg dumbell than it does a 5kg
It takes more force to stop a 5 kg medicine ball than it does a tennis ball
When force < inertia
The object will not move as the force is not strong enough to over come the inertia
Momentum definition
The motion possessed by a moving body
Momentum equation
Momentum = Mass X Velocity (kg.m/s)
Examples of momentum
A non moving object would have zero momentum as it has zero velocity
A player at 90kg and moving at 6m/s will have a momentum of 540kg m/s
Rules of momentum
When 2 objects have the same mass but different velocities the one with greater velocity will produce more momentum
When 2 objects have the same velocity but different mass the one with higher mass will have the higher momentum
Collision and momentum
When 2 objects collide they move in the same direction of the greatest momentum, mass remains the same so only velocity changes.
Principle of Conservation of Momentum
The total momentum of the system before the collision is equal to the total momentum after the collision
Example of Conservation of Momentum
When hockey ball is on the ground the momentum is zero because velocity is zero. Because the ball has zero momentum the momentum before the collision is only equal to the movement of the hockey stick, hitting the ball. After the ball is hit the stick slows to a zero velocity but the ball continues at a velocity that gives the same momentum as before the ball was hit
Summation of momentum
The sequential and coordinated movement of each body segment to produce maximum velocity.
Generating maximum velocity (summation of momentum)
Is generated in a sequential manner, from the body parts closest to the centre of gravity to those further away
Example of summation of momentum
When throwing, the momentum generated in the lower body is transferred to the hips and trunk then to shoulders, elbow and finally to the wrist. Larger body parts generate the most force as they have more energy that is transferred to the wrist for throwing
Impulse definition
The product of a force and the time period over which it is applied, which is equal to the change in momentum of an object
Impulse equation
Impulse = Force X Time (Nxs)
Different impulses
Applying a large force over a long period of time
Applying a large force over a short period of time
Applying a small force over a long period of time
Applying a small force over a short period of time
Examples of impulse
Golfers applying a large force over a short time
Shot putters applying a large force over a long time
Lawn bowlers applying a small force over a short time
Catching a table tennis ball is applying a small force over a short time
Manipulating impulse for reducing injury risk
Giving when catching the ball increases the time at which the force is applied and stops the force causing injury
Newtons first law of motion
Law of Inertia
A body will remain at rest or in uniform motion in a straight line unless acted upon by an external force
Examples of Newtons first law of motion
A soccer ball won’t be moved unless kicked
A tennis ball will keep going up until gravity acts upon it
Newtons second law of motion
Law of Acceleration
A force applied to an object will produce a change in motion (acceleration) in the direction of the applied that is directly propotional to the size of the force
Acceleration in terms of force and mass
Acceleration is proportional to force
Acceleration is inversely proportional to mass
Acceleration definition
The change in speed with respect to time, measure as m/s/s or m/s^2
Examples of Newtons second law in motion
In soccer when kicking the ball to a player far away maximum force is to be applied by applying maximum acceleration to the mass to move it as far as possible.
Newtons third law of motion
Law of action-reaction
For every action, there is an equal and opposite reaction
Examples of Newtons third law of motion
When a ball hits a racquet the racquet applies a force to the ball to move it forward but the ball also applies a force onto the racquet which pushes the string back
When running the ground and the weight of our body pushes against it and the ground pushes back up with an equal force
Newtons first law of angular motion
A body has a reluctance to change the state of angular motion unless acted upon by a torque
Newtons second law of angular motion
A torque applied to an object will produce a change in angular motion (acceleration) in the direction of an applied torque that is directly proportional to the size of the torque and inversely proportional to the moment of inertia od the object
Newtons third law of angular motion
For every torque there is an equal and opposite torque
Torque definition
The turning effect caused by an eccentric force
Angular momentum definition
The quantity of angular motion of an object
Moment of inertia definition
The resistance of an object to change its angular motion
Angular momentum equation
Angular momentum = Moment of inertia X Angular Velocity
Moment of inertia equation
Moment of inertia = Mass X Radius^2 (kgm^2)
What impacts the difficulty to change angular motion?
Moment of inertia - a larger moment of inertia takes more force to move
How does the position of mass impact on the moment of inertia?
An object whose mass is located closer to the axis of rotation is much easier to rotate than one whose mass is distributed further away
Examples of decreasing moment of inertia
Children have lighter bats to decrease moment of inertia as the bat has less mass and a smaller radius of rotation which makes it easier for children to handle
Conservation of angular momentum
Angular momentum is conserved duting flight
When angular momentum is conserved their must be a trade off between angular velocity and moment of inertia.
Somersault example of conservation of momentum
At the beginning of the flip the moment of inertia is high as the radius of rotation is high. The angular velocity is low as the individual is not moving very fast. As the turn begins the moment of inertia is decreased as the radius of rotation is decreased and the angular velocity increases as they can move faster as MOI is low. When landing the person straightens out increasing radius of rotation and moment of inertia therefore slowing down the angular velocity to allow individual to land.
