Transcript BIOMECHANICS

BIOMECHANICS
Biomechanics is the study of
the internal and external
forces which act on the body,
and the effects produced by
those forces.
• Biomechanics is a very useful science in
the study of human performance
especially in the area of perfecting
technique.
• Biomechanics forces may be either
• a) static – which is concerned with bodies
at rest, or
• b) dynamic – which is concerned with
forces producing movement
MOTION
• TRANSLATORY – this is when all parts of the body
follow parallel lines. There are two types:
• Linear – all parts of the body move in straight
parallel lines
• Curvilinear – all parts of the body move in curved
parallel lines.
• ANGULAR, or ROTARY – This when a body moves
about an axis. There are two types:
• Internal Axis – the axis is within the body
• External Axis – the whole body travels around an
axis that is outside the body
GENERAL MOTION
• Most motion is in fact a
combination of both
angular and linear and we
describe this as GENERAL
motion.
• For example a cyclist has
angular motion with the
wheels, the pedals, and his
limbs, but the bike frame
and his trunk experiences
linear motion.
PROJECTILE
MOTION
What is a projectile?
Any body released into the air is a projectile.
This means that once it is in the air it has no
extra propulsion. A body can be released
into the air by either –
Throwing – eg. Discus,
Striking – eg. tennis
Projecting the body itself – eg. High jump
The TRAJECTORY
(path of a projectile)
is influenced by two sets of
factors
 Propelling factors
(ie factors at its
release)
 Speed of release
 Height of release
 Angle of release
 Factors in the air
 Gravity
 Air resistance
 Spin
 Aerodynamics
Effects of Air Resistance and
Aerodynamics
 A - No air Resistance
 B – Air resistance
http://www.walterfendt.de/ph11e/projectile.htm
 We can draw some conclusions
 Speed of release - The greater the speed of
release, the greater the horizontal distance
 Height of release – the greater the height of
release, the greater the horizontal distance
 Angle of release – There is an optimum angle
of release for each object, but that will depend
on a number of factors including aerodynamics
of the object and height of release eg. In
Volleyball, what advantage is there in a jump
serve?
 What
happens
when we
have
different
angle of
release?
Angle of release
look at the requirements
for different activities
 Activity
 Angle (degrees)
 Tennis Serve
 -3 to 15
 Volleyball float serve  13 to 20
 Long jump
 17 to 22
 Discus
 35 to 39
 High jump
 40 to 50
 Standing back
 75
somersault
What are the different objectives for our
projectiles?
And, what do we need to do to maximise our
chances of success?
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Height eg high jump, pole vault
Maximum possible speed of release
Maximum possible angle of release
Distance eg discus, long jump
Maximum possible speed of release
Correct angle of release for activity
Application of spin in some cases
Speed eg rugby pass
Maximum possible speed of release
Lowest possible angle of release
Accuracy eg archery, netball
LEVERS
Biomechanics and Levers
• A lever is a mechanism made up of a lever arm (with 2
forces acting on it) and a pivot point. It has three parts
• The Fulcrum or Pivot point - The point about which
the lever works
• Load or Resistance - The force being overcome by
the lever system
• Effort or Force - The force being applied to overcome
the load
• There are three classes of levers • 1. First class
- See-saw and Crowbar
• 2. Second class
- Wheelbarrow
• 3. Third class
- The boom of a crane
1st Class Lever
The
fulcrum lies
between the
effort and
the load
nd
2
Class Levers
 The fulcrum
lies at one
end of the
lever arm with
the Effort
being applied
at the other
end
rd
3
Class Lever
 The fulcrum
lies at one
end of the
lever arm with
the effort
being applied
between it
and the load
3 classes of levers
INERTIA
• Inertia is a bodies resistance to change in
motion.
• Inertia is described in Newton’s First Law
• “A body continues in it’s state of motion or rest
unless acted on by a force”
• Inertia is related to mass well as shape and
friction
• http://www.physicsclassroom.com/Class/newtla
ws/U2L1b.html
Inertia in Action
• Inertia is easily observed if you think about
being in a vehicle. When it brakes hard,
you are thrown forward. This is because
you have your own moving inertia. When
the vehicle alters its own inertia you still
continue with yours until a force works on
you
NEWTON’S THIRD LAW
• http://www.physicsclassroom.com/Class/newtla
ws/U2L4b.html
• Newton’s 3rd law relates to Action / Reaction
• “For each and every action, there is an equal
and opposite reaction”
FORCE SUMMATION
• The velocity of
a projectile
depends on the
speed of the
last part of the
body at the
time of contact
or release
FORCE SUMMATION
• If you wish to achieve
maximum velocity, it is
important that each body
part is used in the correct
sequence.
• You use the strongest,
heaviest muscles first,
before using the smaller,
faster muscles last.
• This overcomes inertia
TIMING
• The timing of the application
of the forces is vital
• A body part should begin to
move when the previous
body part is exerting
maximum force / speed
• Eg. In a well-timed
Volleyball spike; the forearm
begins to extend at the
elbow just as the upper arm
begins to deccelerate