Transcript Biomechanics - PE Studies Revision Seminars

3A/3B BIOMECHANICS
www.flickr.com/photos/8136496@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 Inertia
Define the term vector. Relate to
movement principles.
The principle of Force-Time: muscle
structure; mechanics of the musculoskeletal system; mechanical
characteristics of muscle (force-velocity;
force-length; force-time); Newton’s
Second Law of Motion. impulse –
momentum relationship.
2nd Law of motion
Impulse and momentum are related in
that a change in momentum results in a
proportional change in impulse.
1. muscle structure
2. mechanics of musculo skeletal
system
3. muscle characteristics
Identify possible models for analysis
e.g. Knudsen and Morrison – model for
qualitative analysis.
Models for biomechanical analysis.

Physical Education Studies Elaboration
Support Document, 2008
Movement principles and concepts
Unit: 3B
•Segmental Interaction i.e. Kinematic chain
The principle of Balance: torque
•Dynamical Systems Theory
(moment of force); angular inertia
•Balance
(moment of inertia); equilibrium; centre •Torque
of gravity.
•Angular Inertia (Rotational Inertia)
The principle of Spin: fluids; fluid forces •Centre of Gravity
(buoyancy, drag, lift-Bernoulli’s Principle, •Principle of Spin
the Magnus effect).
•Bernoulli’s Principle
The principle of Segmental Interaction: •Magnus Effect
kinematic chain; corrections in body
•Fluid forces.
positioning and timing; dynamical
•surface drag i.e. swim suits skins
systems theory.
•form drag i.e. golf balls
•wave drag
Physical Education Studies Elaboration
Support Document, 2008
STRUCTURE OF SKELETAL MUSCLE
• Skeletal Muscle surrounded by Epimysium
• Made up of bundles of muscle fibres (fascicles) surrounded by
Perimysium
• Each fascicle contains individual muscle fibres, surrounded by
Endomysium
• Fibres arranged into myofibrils, running parallel to each other &
the length of the muscle fibre.
• Myofibrils contain a chain of sarcomeres, which are composed of
actin and myosin filaments responsible for creating movement
IMPULSE – MOMENTUM RELATIONSHIP
FORCE
FORCE
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?
TIME
TIME
IMPULSE AND ACCURACY
• 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
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
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
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.
Large backswing ensures
maximum force is applied,
but over a short period of
time
Wides stance aims to
maximise impulse by ↑
contact time, however force
generated will be low
compared to the hit
www.flickr.com/photos/mark_fletcher/2325626998/sizes/s/
www.flickr.com/photos/stephanderson/2190910716
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
CONCENTRIC
ECCENTRIC
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
MECHANICAL CHARACTERISTICS OF
MUSCLE
FORCE
FORCE – VELOCITY
During isometric
contraction, force
generated does not result in
change of muscle length
During concentric muscle
contraction (shortening),
max force achieved during
minimum velocity
During eccentric muscle
contraction (lengthening) ,
max force achieved during
max velocity
LENGTHENING VELOCITY
0
SHORTENING VELOCITY
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
RESISTANCE
FORCE
EFFORT
FORCE
EFFORT
ARM
FULCRUM
RESISTANCE
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/
ANGULAR MOMENTUM – MOMENT OF INERTIA
(rotational inertia)
• 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.
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
high, moment of
inertia low
Angular velocity
low, moment of
inertia high
Angular
velocity
Angular
momentum
remains
constant
TIME
TURBULENT FLOW
Late boundary layer
separation
High pressure
at front of ball
Small turbulent
pocket (high
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
Early boundary
layer separation
High pressure at
front of ball
Large turbulent
pocket (low pressure)
at rear of 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
1. PREPARATION
Side on position to
allow for greater force
generation through
sequential summation
of force
2. EXECUTION
PHASE
Movement of big body parts
(legs) followed by rotation of
hips, shoulders, arms and then
wrists
Arms fully extend at point of
contact to ensure longest
possible lever at impact
STRIKING
3. FOLLOW
THROUGH
Follow through
towards the target to
prevent decceleration
of final segment and
ensure safe dissipation
of force