phys ed studies ATAR 12 - biomechanics

force

an interaction between two objects

external: gravity, friction, air or water resistance

internal: actions of tendons and muscles

newtons 1st law

a body will continue in its state of rest or motion unless acted upon by a force

law of inertia

inertia: the amount of resistance to change an objects state of motion

newtons 2nd law

the rate of change of acceleration to a body is proportional to the mass of the object

the greater the force applied the faster the acceleration

law of acceleration

newtons 3rd law

every action has an equal and opposite reaction

momentum

the amount of motion passed by a moving body

p=mv

an object can only have momentum if its moving

conservation of linear momentum

the total momentum of two objects before and after are both equal

imperfect elastic collision

not all momentum is conserved, some is lost

most applicable to sport

perfect elastic collision

all or most momentum is lost

no energy is lost to sound or frictions

the momentum of one object is transferred to another with no change in momentum

impulse

the application of force over time to change momentum

force x time

impulse-momentum relationship graphs

coefficient of restitution (COR)

the amount of energy that remains after an elastic collision

compares height of bounce and the original drop height (0-1)

COR equation - square root of height bounced over height dropped

an object loses energy through noise and friction

COR ratings

1 - represents a perfect elastic collision (rebounds to the same height)

0 - represents a perfect inelastic collision (stops when it hits the surface)

elastic

the property of an object to regains its original shape after impact

3 main factors that affects COR

temperature: as the temperature of the ball increases so does the COR

velocity of collision: when velocity increases the COR reduces because there is a greater compression of the ball - more energy is lost to the collision

equipment and surfaces: condition of the ball - new vs old

material of the ball - rubber is better than a netball

different surfaces - the harder the surface the higher the bounce

material of striking implement - wood causes a lower COR than aluminium

angular motion

all body parts turn on rotation around an axis

full or part circle

how to create angular motion

torque - the amount of eccentric/off centre force (increased force = increase turn)

distance from the centre

torque

a measure of the force that can cause an object to rotate

force x perpendicular distance

moment of inertia

the resistance of rotating an objet to change its state of motion

mass x radius of rotation

factors that contribute to moment of inertia

mass

moment arm - distance from mass to axis of rotation

examples of moment of inertia

normal hammer: the mass is distributed away from the axis of rotation (wrist) makes L higher and makes the hammer harder to rotate but produces more force

upside down hammer: the mass is closer to the axis of rotation which lowers L making it easier to rotate

angular velocity

the rate of rotation - how fast an object rotates (W)

factors that affect velocity

moment of inertia: depends on the mass distribution and axis of rotation

applied torque: increased toque increases the change in angular velocity

mass distribution: mass is distributed in relation to the axis of rotation - when mass is closer to the W it increases

initial angular velocity: starting velocity will influence its subsequent W when no additional forces are applied

angular momentum (L)

the measure of the amount of rotation an object possesses

relation to newton: a body will rotate on an axis unless acted upon by external forces

factors that relate to angular momentum

W - angular velocity - increases for angular momentum

L - moment of inertia - decrease for constant angular momentum

they are interchangeable