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Biomechanics
Chapter 15
Introduction
We have now looked at factors that can
influence our ability to perform at a high
level.
Chemicals we ingest, the equipment we
use, and the training practices we choose
Biomechanics will look at how physical
forces affect performance.
BIOMECHANICS
How physical forces affect human
performance.
The application of the principles of physics
to the analysis of movement.
Biomechanics and careers
Clinical practitioners of biomechanics examine
physical causes and corrective actions to deal
with serious physical injuries
Other practitioners use biomechanical principles
to design sport and office equipment that is
safer, more productive/ efficient and more
comfortable
Prosthetic devices and orthopedic footwear
Scientific models
These include theories and laws
These models reduce things to their essentials
and assist scientists with understanding how
things work in hopes of then using this
knowledge to predict how they will behave and
finally allowing them to influence and manipulate
these things to improve performance
Also creates a universal language and basis for
communication. E.g.. Anatomical position
Newton’s Model
Sir Isaac Newton created this model in
1687. “The Three Laws of Motion”
Explained how forces worked and became
the basis for modern physics and thus
biomechanics as well
Law of Inertia
Law of Acceleration
Law of Reaction
LAW OF INERTIA
An object in motion remains in motion
unless acted on by an external force.
LAW OF INERTIA…more
An object at rest remains at rest unless
acted on by an external force.
Law of Inertia
States that a body will remain at rest or in a state
of constant motion (equilibrium) unless acted
upon by an external force.
E.g. Human body ---remain standing unless
external force is applied (muscle contraction,
wind, someone else)
Why does a Javelin eventually hit the ground?
- Eternal forces acting on it (gravity, wind
etc.)
LAW OF ACCELERATION
Force = mass X acceleration (F = ma)
*Think* (15 = 3 x 5)
Law of Acceleration
F=ma
Force equals the product of mass and
acceleration
A force applied to a body causes an
acceleration of that body of a magnitude
proportional to the applied force and in the
direction of the applied force and inversely
proportional to the body’s mass ***( Thus,
a=F/m)
Newtons
Force is measured in Newtons (N)
1N = 1 (kg) (m) / (s2)
Gravity is a pulling force which is exerted
on us by the earth and it occurs at a rate
of 9.8 m/s2
Thus, something that is 102 grams or
0.102 kg would have a weight of 1 N on
earth. ( 0.102 x 9.8 = 1N)
***1000 grams = 1kg
Weight vs. Mass
Weight and Mass are not the same!
On the moon a person would have the same
mass as they do on earth but they would have
less weight. Weight is affected by the force of
Gravity and since there is more gravity on
earth as compared to the moon you would
weigh more on earth.
Mass= amount of stuff (molecules etc. that make
up an object). Mass is constant and unaffected
by gravity.
Types of motion
Linear motion
Movement in a
particular direction
Force acts through
the centre of mass
Angular Motion
Movement around an
axis
The force does not
act through the centre
of mass. Rather it is
off centre which
results in rotation
http://www.youtube.com/watch?v=MNDB5
QU5bBY
105 MPH !
Rotational/Angular Motion
Slightly different than Linear motion
- Instead of acceleration we have angular
acceleration
- Instead of Force we have a moment of
force (torque)
- Instead of mass we have a moment of
inertia.
Angular motion cont..
Just like Mass this is the resistance to
rotation/movement. The larger the
moment of inertia the larger the
moment of force required to spin or
stop spinning.
In other words, the further the mass is
from the axis, the greater the moment of
inertia and thus the harder it is to start or
stop spinning and vice versa.
Rotation principles
Figure skater pg 229. As the skater brings their
arms into the centre of their body their angular
acceleration increases because they have
reduced their moment of inertia.
Gymnastics---following a series of rapid
somersaults in mid air the athlete straitens out
their body. By opening up they increase their
moment of inertia and slow down as they
prepare to land. (i,e. the force stays the same
and there is now a larger moment of force thus
the body slows down
Figure skating
Law of Reaction
When a body exerts a force on a second body
the second body exerts a reactive force on the
first body that is equal to the magnitude of the
initial force but inn the opposite direction.
Every action has an equal and opposite reaction
As a person jumps up….there is a force exerted
by the quadriceps on the ground and there is an
equal and opposite force from the ground on the
person which causes them to elevate.
LAW OF REACTION
Every action has an equal and opposite
reaction.
LAW OF REACTION…more
Another example…
TYPES OF FORCES
Internal Forces – e.g. muscles pulling on
bones.
External Forces – e.g. gravity, contact with
ground, environment (wind), sport
equipment, opponent, etc.
KINEMATICS vs. KINETICS
Kinematics
– Study of space and time aspects of
movement, e.g. how far and how fast things
travel.
– Deals with time, displacement, velocity, and
acceleration.
– Deals with numbers.
KINEMATICS vs. KINETICS
Kinetics
– What causes the motion?
– Focuses on the various forces that are
associated with motion.
– The forces producing or resulting from the
movement.
– Descriptions of forces.
Homework
Read and make notes on Linear vs.
Rotational motion
Lever systems
– What type of lever is working when you kick a
soccer ball (knee)
– When you perform a lateral arm raise with a
10 pound weight
– Wheel barrow?