3A/3B BIOMECHANICS N05/2562423599.
-
Upload
sophia-vaughn -
Category
Documents
-
view
218 -
download
0
Transcript of 3A/3B BIOMECHANICS N05/2562423599.
Movement principles and concepts
Unit: 3A
Scope & Sequence Elaboration
The principle of Inertia: Newton’s First Law of motion; mass; contact forces
Newton’s first law - Principle of InertiaDefine the term vector. Relate to movement principles.
The principle of Force-Time: muscle structure; mechanics of the musculo-skeletal system; mechanical characteristics of muscle (force-velocity; force-length; force-time); Newton’s Second Law of Motion. impulse – momentum relationship.
2nd Law of motionImpulse and momentum are related in that a change in momentum results in a proportional change in impulse.1. muscle structure2. mechanics of musculo skeletal
system3. muscle characteristics
Models for biomechanical analysis. Identify possible models for analysis e.g. Knudsen and Morrison – model for
qualitative analysis.
Physical Education Studies Elaboration Support Document, 2008
•Segmental Interaction i.e. Kinematic chain•Dynamical Systems Theory•Balance •Torque•Angular Inertia (Rotational Inertia)•Centre of Gravity•Principle of Spin•Bernoulli’s Principle•Magnus Effect•Fluid forces.
•surface drag i.e. swim suits skins•form drag i.e. golf balls•wave drag
The principle of Balance: torque (moment of force); angular inertia (moment of inertia); equilibrium; centre of gravity.The principle of Spin: fluids; fluid forces (buoyancy, drag, lift-Bernoulli’s Principle, the Magnus effect).The principle of Segmental Interaction: kinematic chain; corrections in body positioning and timing; dynamical systems theory.
Movement principles and concepts
Unit: 3B
Physical Education Studies Elaboration Support Document, 2008
TIME TIME
Which method would you prefer to use when catching a ball – a large force over a
short period of time or a smaller peak force over a longer period of time?
IMPULSE – MOMENTUM RELATIONSHIP
• FLATTENING THE SWING ARC– Good technique can↑ contact time with a ball during collision sports
• May provide opportunity for ↑ force application in desired direction (hockey drag flick)
• May also provide ↑ accuracy, however usually occurs with a ↓ in force application
IMPULSE AND ACCURACY
Flattening the arc increases the likelihood of application of
force to object in desired direction of travel by creating
a zone of flat line motion
A more curved arc reduces the likelihood of a successful outcome by reducing the
opportunity for application of force in the intended direction
of travel
Wides stance aims to maximise impulse by ↑
contact time, however force generated will be low compared to the hit
IMPULSE AND SPORT
• Because impulse is force * time, we can change either one to suit the demands of the situation
1. INCREASING MOMENTUM• In hockey a hit will place a large force, but over a small time. A
drag flick would use a smaller force over a longer period of time. Either way the ball will increase its momentum
• Ideally we look to maximise both force and time, however the human body rarely allows for this to happen.
www.flickr.com/photos/mark_fletcher/2325626998/sizes/s/ www.flickr.com/photos/stephanderson/2190910716
Large backswing ensures maximum force is applied, but over a short period of
time
IMPULSE AND SPORT
2. DECREASING MOMENTUM• A cricket ball is hit towards a fielder. The fielder wishes to stop
the ball (take momentum back to zero).– Would he apply a large force over a short period of time– Would he apply a small force over a longer period of time.
• Which method is likely to be more successful in catching the ball?• Therefore in stopping a force we usually increase the time
component so we can reduce the peak force!
MECHANICAL CHARACTERISTICS OF MUSCLE
FORCE – VELOCITY– Muscle can create ↑ force with a ↓ velocity of concentric contraction– Muscle can resist ↑ force with a ↑ velocity of eccentric contraction
Its easier to lift a heavy weight concentrically (upwards) slowly
than it is quickly!
Its easier to resist a heavy weight eccentrically
(lowering) quickly rather than slowly
CONCENTRIC ECCENTRIC
FORCE – VELOCITY
MECHANICAL CHARACTERISTICS OF MUSCLE
LENGTHENING VELOCITY SHORTENING VELOCITY0
During eccentric muscle contraction (lengthening) , max force achieved during
max velocity
During concentric muscle contraction (shortening),
max force achieved during minimum velocity
During isometric contraction, force
generated does not result in change of muscle length
LEVERS - ANATOMY
• Fulcrum – point around which the lever rotates• Effort Arm – The part of the lever that the effort force is applied to
(measured from the fulcrum to the point at which the force is applied)
• Resistance Arm – The part of the lever that applies the resistance force (measured from the fulcrum to the center of the resistance force)
• Input (Effort) Force – Force exerted ON the lever• Output (Resistance) Force – Force exerted BY the lever
FULCRUM
EFFORT FORCE
RESISTANCE FORCE
RESISTANCE ARM
EFFORT ARM
LEVERS - PRINCIPLES• Velocity is greatest at the distal end of a lever
– Longer the lever, greater the velocity at impact– E.g. Golf driver vs. 9 iron
• ↑ club length creates ↑ velocity and momentum at impact provided the athlete can control the longer lever – longer generally means↑ mass!
• Children often have difficulty with this and subsequently use shorter levers to gain better control – shorter cricket bat, tennis racquet etc
www.flickr.com/photos/flash716/2578346899/ www.flickr.com/photos/cwalker71/2455913000/
• If the body’s mass is close to the axis of rotation, rotation is easier to manipulate. This makes the moment of inertia smaller and results in an increase in angular velocity.
• Moving the mass away from the axis of rotation slows down angular velocity.
ANGULAR MOMENTUM – MOMENT OF INERTIA (rotational inertia)
Try this on a swivel chair – see which method will allow you to spin at a faster rate? Note what happens when you move from a tucked position (left) to a more open position (right).
CONSERVATION OF ANGULAR MOMENTUM
Angular momentum
Moment of inertia
Angular velocity
TIME
Angular velocity high, moment of
inertia low
Angular velocity low, moment of
inertia high
Angular momentum
remains constant
TURBULENT FLOW LAMINAR FLOW
High pressure at front of ball
High pressure at front of ball
Small turbulent pocket (high
pressure) at rear of ball
Large turbulent pocket (low pressure)
at rear of ball
Turbulent flow causes the boundary layer separation to take place later. This causes a smaller pressure differential between the front and back of the ball as their is only a small pocket of turbulent
wake at the rear of the ball
Laminar flow causes the boundary layer separation to take place earlier. This causes a larger pressure
differential between the front and rear of the ball as their is now a large pocket of turbulent wake at the
back of the ball
Late boundary layer separation
Early boundary layer separation