biomechanics

what is momentum

a measure of the amount of motion possessed by a moving body, mass x velocity

• only have momentum if moving

• greater the momentum, the more force need to stop or slow

what is impulse

the application of force over a period of time to change the momentum of an object, force x time

how to increase momentum

• increase both force and time components

• force is increased through effective summation of force and improved strength

• time is increased through technique and equipment modifications

how to decrease momentum

• increase time component

• e.g. bringing arms down with ball when catching

what is coefficient of restitution

measures the elasticity between an object and a given surface

• measures how much energy remains in the object after collision

• 1= perfectly elastic collision

• 0= perfectly inelastic collision

factors affecting COR

1. equipment and surfaces

   • condition of balls (new (high) old (low))

   • type of equipment being used (wood (low) or metal (high))

   • type and condition of playing surface (clay court (high) grass court (low))

2. temperature of balls

   • increase in temp, increases COR

3. velocity of collision

   • increased velocity = decreased COR

what does a high or low COR mean

• a high COR means the object regains it shape quickly, resulting in little energy being lost upon collision with the surface

• a low COR means the object regains it shape slowly, resulting in lots of energy being lost upon collision with the surface

what does angular momentum mean and the components

• angular momentum: the quantity of angular motion possessed by a rotating body, m.o.i x angular velocity

• moment of inertia: the resistance of a rotating object to change its state of motion

• angular velocity: the rate of change in angular position of a body

when can m.o.i change

• mass distributed close to axis, the m.o.i is small and easy to rotate

• mass is further away from axis of rotation, m.o.i increases and rotation is harder

equation for m.o.i and meaning

• m.o.i = mass of object x radius of rotation

• mass of object: mass

• radius of rotation: how the objects mass is distributed about the axis of rotation

what is the conservation of angular momentum

indicates a rotating body will continue to rotate indefinitely unless an external force acts on it

• can be controlled by expanding body or decreasing body

what is a third class lever

the axis is located at one end, with the application of the force in the middle and resistance applied at opposite end

• most common type in human body

how can a third class lever be a speed multiplier

• when one end of the lever travels a greater displacement over the same period, the velocity at the distal end is greatest creating a speed mulitplier

what are the acronyms for three types of levers and example

• 1st: R A F - neck

• 2nd: F R A - ankle (gastrocnemius)

• 3rd: R F A - bicep

what is fluid mechanics and the forces of interest

the natural science of fluids (liquids and gasses) in motion

• drag (impacts horizontally)

• lift (impacts vertically)

what is a boundary layer and it can be…

a thin layer of air surrounding or ‘attached’ to the ball

• laminar: a type of fluid flow in which fluid moves smoothly in individual layers or streams

• turbulent: flow in which the velocity at any point varies erratically

what is boundary layer separation

where the boundary layer breaks away from the ball

• the earlier, the greater the pressure gradient between front and back of ball, leads to increased drag

factors that affect boundary layer separation

• velocity

• surface roughness

• shape

what is fluid resistance

as an object moves through a fluid (air/water) it disturbs it. the greater the disturbance, the greater the transfer of energy

fluid resistance can be affected by…

1. density (air): denser, more disturbed, greater resistance

2. viscosity (liquid): more viscous, more disturbed, greater resistance

types of drag

• form drag

• surface drag

• wave drag

what is surface drag

the friction produces between fluid and the surface of a moving object

what factors can affect surface drag

• relative velocity of moving object

• relative roughness of object

• viscosity of the fluid

• surface area of object

what is pressure drag/form drag

the resistance created by the pressure differential between the front and back of an object moving through a fluid

factors affecting form drag

• the cross sectional area of the object presented to the fluid

• velocity of object

• surface roughness

• shape of object

what is wave drag

the creation of waves forms resistance at the point where air and water interact

OR

when a body moves through the water, it causes waves to be generates, causing resistance to movement

factors affecting wave drag

• relative velocity of the wave

• technique

• open water vs closed water

factors affecting drag

• drag coefficient

• mass

• velocity

• surface roughness

• cross sectional area

• shape

lift

the component of force that acts perpendicular to the direction of flow

• only occurs in objects that are spinning and not perfectly symmetrical

• created by pressure differentials

bernoulli’s principle

relates to the pressure created from a moving fluid over an object, whereby fast flowing fluid produces a low pressure area and slow moving fluid produces a high pressure area

how does a car stick to the ground

• a high pressure zone above the car

• low pressure zone below the car

• downward pressure causing stick

magnus effect

the term used to describe the effect of rotation on an objects path as it moves through a fluid

• explains the effect spin has on trajectory or flight path

what is an example of the magnus effect

• when ball is struck with eccentric force

• the rotating ball interacts with oncoming air, and the curve is magnus effect

topspin

• causes ball to drop or dip and travel shorter in flight

• the ball can be hit with more velocity impacting opponents time to return the shot

backspin

• causes ball to rise higher and travel further, applies for activities achieving maximal distance

• can be used to keep ball in play/ give player time to get back

sidespin

• cause ball to curve left or right depending on force application

• can be used to curve ball away from opponents reach/ around and obstacle

balance

the ability to neutralise forces that disturb equilibrium

factors that effect balance

1. size of base of support

2. height of centre of gravity above the base of support

3. position of line of gravity relative to base of support

4. mass of object

segmental interaction and what two factors is it centred around

force acting between the segments of a body can transfer energy between segments

1. power: more segments used, forces sequentially summated

2. accuracy: less segments used, forces simultaneously summated

simultaneous summation

• where all body parts move at the same time to produce a force

• produce accuracy

• e.g putt golf

sequential summation

• sequential combination of force produces by different parts of the body, acting together to maximise force

• e.g. baseball pitcher

6 steps to sequentially produce maximal force

1. the stronger and larger muscles of the thighs and trunk are moved first, followed by smaller and faster muscles

2. sequentially accelerate each body so optimum momentum passes from on body part to the next

3. each body part should be stable so that the next body part accelerates around a stable base to transfer momentum

4. use as many body parts as possible to apply force over the maximum possible time

5. follow through is important to prevent deceleration of the last segment and ensure safe force dissipation

6. ensure all forces are directed towards the target

optimal projection

the relationship between the angle, velocity and height of release/landing height to attain the athlete goal

how can athletes maximise distance

• maximise velocity; through biomechanical principles

• maximise height of release; without sacrificing velocity of release or stability

• angle of release; 40-43 degrees to max distance