Transcript Biomechanics An overview  Biomechanics can be used to:      Refine technique Prevent injury Develop equipment Correct errors Whilst many biomechanical principles are inherent in each sport skill, it.

Biomechanics
An overview
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Biomechanics can be used to:
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Refine technique
Prevent injury
Develop equipment
Correct errors
Whilst many biomechanical principles are inherent in each sport
skill, it is important to discern the most influential principles in
your sport in order to look to optimising technique
Topics
 Motion
 Balance
and Stability
 Force Production
 Momentum
 Rotary Forces
 Levers
 Projectile Motion
 Fluid Mechanics
Motion
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To initiate motion, one must overcome inertia.
Once in motion, factors such as velocity and acceleration
become influential.
Motion can be curvilinear or rectilinear
Factors such as velocity and acceleration are variable amongst
athletes and can determine the effectiveness of one’s
performance.
Curvilinear motion
Rectilinear motion
Newton’s Laws of Motion
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Newton’s first law of motion states that a still object continues to
be still, and a moving object continues to move at its current
velocity, unless an external force acts on the object.
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His second law states that the sum of the force that moves an
object is equal to the object’s mass multiplied by the
acceleration. This law can be expressed as the following
equation:
Force = mass × acceleration
(F = ma)
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Newtons law of action reaction states that for every action there
is an equal and opposite reaction
Balance and Stability
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Every athlete must be able to maintain stability and balance.
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Failure to do so can result in loss of force and or accuracy.
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Balance can be dynamic or static.
Personal reflection:
Do you find balance easier
when you are moving or
stationary? How does this
affect your performance in
your current physical
activity?
Balance and Stability
Personal reflection:
Have you ever done
the stork stand
balance test? Did you
find it challenging?
Centre of gravity
Personal reflection:
Think of a time when you
were performing a dynamic
movement. When your
centre of gravity falls
outside of your body, what
is your natural movement
to try to correct it?
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The height of the centre of gravity can have a significant affect
on one’s stability.
Personal reflection:
Do you think your height
has an effect on your
stability?
Force
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Force is anything that causes or has the potential to cause the
movement, diversion or slowing of the object on which it acts.
All forces have four common properties. They have:
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magnitude (an amount, or how much is applied)
direction (the angle at which the force is applied)
a point of application (the specific point at which
the force is applied)
a line of action (represented by
a straight line through the point of
application in the direction that
the force is acting).
Force
Integration:
Consider the sport you are
currently studying. Describe
the forces required in terms of
the four properties listed on
the previous slide.
Force
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Force production: Most sports require an athlete to be able to
both generate and control forces.
Integration:
In your sport, can you
differentiate between the
skills that require maximum
force and those that require
control and accuracy?
Summation of Forces
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To obtain maximum force, it is necessary to combine or add up
the forces applied by different body parts. This concept is
known as the summation of forces.
The summation of force is influenced by the:
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number of body parts used in the movement
order and timing of their involvement
force and velocity generated
way in which the body and body parts are stabilised and
balanced.
The long jumper combines the
forces in his legs, abdominals and
arms to propel himself further
into the pit
Summation of Forces
Personal reflection:
Choose one physical
skill from your current
sport. Which body parts
do you use to produce
maximum force? In what
order?
Momentum
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Whether it is a sprinter running along a track or a bowling ball
rolling down an alley, it has a certain mass and a certain velocity.
The product of these is known as the momentum
Personal reflection:
When you sprint, how many
steps does it take you to come
to a complete stop? How does
this compare with your
classmates or competitors?
Why?
Momentum
In most sports, mass is
constant, so velocity
becomes the main factor
influencing momentum.
So, to increase momentum,
simply increase velocity.
Momentum
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In many sports, it is necessary for momentum to be transferred
to another object or body part. The greater the momentum an
object has, the greater its effect on other objects it collides with.
Personal reflection:
Have you ever played pool?
Why is that when the
white ball strikes another
ball straight on, the white
ball stops moving while the
ball that was struck moves
forward?
Momentum
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Stabilisation must occur for effective transfer of gained
momentum
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For example, in tennis it is common for athletes to brace (tense
up) their muscles just before the impact of a forehand. Stopping
the rotation of the body by bracing causes a whip-like effect on
the arm
Accuracy
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It is important in many sports to be accurate in the production of
sport in both direction and magnitude.
Application:
In the following sporting
situations, consider ways in which
the performer can increase their
directional accuracy.
1. Batting into space in softball
2. Digging to a setter in volleyball
3. Kicking a penalty goal in soccer
Rotary Forces
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Not all forces are produced in straight lines.
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Concentric forces are applied through the centre of an object and cause
motion in a straight line
Practical example:
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Eccentric forces are applied
off-centre and cause rotation
in the object to which the force
is applied.
Place your textbook on the
desk in front of you. Push
the book away from you
with two fingers, applying
the force through the centre
of the book. Now repeat
this, applying the force to
one side of centre. What do
you notice?
Rotation about an axis (Torque)
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More torque, and a greater rotation or twisting movement, will be
generated when more force is applied further from the centre of
an object.
Rotational Momentum
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A spinning object will have momentum that will allow it to
continue to spin until an external force is applied.
Practical example:
Sit on a swivel chair and clear a
space around the chair. Ask a
friend to gently spin the chair in
any direction. You can control
the speed at which you spin by
tucking your legs into your body
to speed up and extending them
out to slow down.
The velocity of the
spin is affected by
the distribution of
the weight from the
axis of the object.
Rotational Momentum
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When spinning on the ice, skaters can control the rate of spin by
moving their limbs closer to the axis of rotation (to rotate faster)
or extending their arms and legs (to rotate more slowly).
Centrifugal and centripetal forces
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Centripetal force is the force that causes rotating objects to move
towards the centre, or axis, of rotation.
Centrifugal force is the force that causes rotating objects to move
away from the centre, or axis, of rotation.
Levers
Three types:
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First class: fulcrum between the force
and the resistance e.g. oar on row
boat.
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Second class: resistance between the
force and the fulcrum
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Third class: force between the
resistance and the fulcrum
(e.g. baseball batter).
Levers
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Third class levers are the most
common in sport.
Sports using bats or racquets all use
third class levers.
The velocity of a lever is fastest at
the point furthest from the fulcrum.
By increasing the length of the bat,
the velocity is increased.
It is important to consider strength
and accuracy when looking at
levers.
It is not ideal to use a 4m long bat/
racquet even if a greater velocity
could to produced.
Maximising leverage
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Due to inertia, a shorter lever is easier
to move than a longer one.
To maximise the efficiency of a lever, it
is often better to begin a lever’s motion
by shortening the lever.
This can be achieved by bending the
relevant joint.
e.g. a soccer playing kicking a ball
starts with a bent knee, a javelin
thrower bends the elbow to bring the
javelin through and a tennis server
bends their elbow before extending to
hit the ball.
The ‘Sweet Spot’
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The sweet spot is the point that, when struck, causes no
backwards nor forwards rotation of the bat.
Personal reflection :
Have you ever felt the
effects of hitting a ball
outside the sweet
spot?
Projectile Motion
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Factors that influence flight
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Height of release
Angle of release
Speed of release
Gravity and air resistance
Angle of release
The optimal trajectory of a projectile is just less than 45 degrees
Height of release
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A projectile thrown from a height will travel further.
Personal reflection:
Do you think you have a
height advantage when
throwing?
The effects of spinning
The Magnus effect explains
how a spinning projectile,
such as a ball, curves in
flight.
Fluid Mechanics
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Fluid mechanics refers to forces that operate in both the water
and in air (gravity, resistance, propulsion, and bouyancy).
Buoyancy
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An object’s buoyancy determines whether or not it will float.
Buoyancy is influenced by density.
Density is a measure of mass in relation to volume.
The high density muscle
and bone in our legs
cause them to sink when
in the water whilst the low
density air and fat in our
chests, keep this body
part afloat.
Personal reflection:
Have you ever tried
floating on your back in
water? What happens
when you allow your
body to relax?
Centre of Buoyancy
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The centre of buoyancy of a
floating object is different to its
centre of gravity.
In swimmers, the centre of
buoyancy can change
depending on the position and
movement of a swimmer’s body,
particularly the legs, and how
much of the body is submerged.
A swimmers’ centre of
buoyancy is closer to their
heads due to the lower density
of the chest and core compared
to the legs.
Propulsion
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Swimmers are required to both push and pull themselves
through the water.
In this pushing and pulling action the forces of lift and drag are at
work.
Lift
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Lift force occurs due to the
factors involved in
Bernoulli’s Principle.
The difference in velocity of
the water travelling over the
surface of the hands
creates a pressure
difference that, when
applied correctly, creates
lift.
Drag
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Drag force opposes the forward
movement of a swimmer, providing
resistance.
Swimmers can minimise this effect
of drag by streamlining their bodies
and pitching the entry of their hands
to ensure the water surface is cut
cleanly.
Drag can also assist a swimmer. Lift
and drag can work together to
create propulsion
Water resistance
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Skin resistance is the resistance created by water ‘gripping’ the
skin as is passes through.
Turbulence resistance is created due to the high pressure
created at the front of the swimmer interacting with the low
pressure formed at the rear of the swimmer, creating a suction
effect.
Water resistance
Wave resistance is caused
by the wall of water that
builds up at the front of a
swimmer, blocking their
path.