Principles of
Biomechanical
Analysis
PSE4U
Mr. MacMillan
Review of Biomechanics
 The



Laws of Motion
1st – Law of Inertia
2nd – Law of Acceleration
3rd – Law of Reaction
 Types

of Motion
Linear
 Movement
in a particular direction
 Sprinter accelerating down a track

Rotational
 Movement
about an axis
 What are the three axis’?

Longitudinal, anterio-posterior, horizontal
 Ice
skater spinning or a gymnastic somersault
 Linear


Motion
Acceleration in a straight line
Force as a vector
 Force
as a pull or push of a certain
magnitude in a certain direction
 Rotational




Motion
Is comparable to linear motion but the
object spins around an axis
Acceleration is angular
Torque is measured rather than force
Moment of inertia
 Resistance
to rotation
 Larger the moment of inertia, the
larger the moment of force needed
to maintain the same angular
acceleration
Linear and Rotational Motion
Linear Motion
Rotational Motion
Displacement
Angular Displacement
Velocity
Angular Velocity
Acceleration
Angular Acceleration
Force
Moment of Force (torque)
Mass
Moment of Inertia
Ice Skating
The ice-skater begins to spin with
arms spread apart then suddenly
brings them closer to the body.
The end result of tightening up is
that the skater’s spin (angular
velocity) increases, seemingly
miraculously
Gymnastics
Following a series of rapid
somersaults in a tight position, the
gymnast does a forward flip with
the body positioned more or less
straight. By opening up, the
gymnast increases the moment
of inertia, thereby resulting in a
decrease in angular velocity
Diving
After leaving the high diving
board, the diver curls tightly
and then opens up just before
entering the water. By opening
up before entry, the diver
increases the moment of
inertia, thereby slowing down
the angular velocity and
hopefully ensuring a smooth
and safe entry.
The Lever Systems
 Class
I Lever
 Class II Lever
 Class III Lever
 The
fulcrum (axis)
is located
between the
force (effort) and
the resistance
(load)
Class I Lever
(e.g. teeter-totter)
 The
resistance is
between the
fulcrum and the
resistance
Class II Lever
(e.g. wheelbarrow)
 The
force is
between the
fulcrum and the
resistance
Class III Lever
(e.g. snow shovel)
Seven Principles of
Biomechanical Analysis
1.
2.
3.
4.
5.
6.
7.
Stability
Maximum force
Maximum velocity
Impulse
Reaction
Torque
Angular momentum
Principle 1:
 The
lower the centre of
mass, the larger the base of
support, the closer the
centre of mass to the base
of support and the greater
the mass, the more stability
increases.
Principle 2:
 The
production of maximum force
requires the use of all possible joint
movements that contribute to the task’s
objective
Principle 3:
 The
production of maximum velocity
requires the use of joints in order – from
largest to smallest
Principle 4:
 The
greater the applied impulse, the
greater the increase in velocity
Principle 5:
 Movement
usually occurs in the direction
opposite that of the applied force
Principle 6:
 Angular
motion is produced by
application of force acting at some
distance from an axis, that is, by torque
Principle 7:
 Angular
momentum is constant when an
athlete or object is free in the air.
Free Body Diagrams



Free body diagrams, are a tool for solving problems with
multiple forces acting on a single body.
The purpose of a free body diagram is to reduce the
complexity of situation for easy analysis. The diagram is used
as a starting point to develop a mathematical model of the
forces acting on an object.
Below is a picture of a flying jet.

Force = m a



M = mass
A = acceleration
Acceleration

= (v – u) / t




Momentum = m v



M = mass
V = velocity
Impulse (N/s)

= Ft = m Δv



V = final velocity
U = starting velocity
T = time
M = mass
Δ v = average velocity
Change in Momentum

= m (V2 – v1)



M = mass
V2 = final velocity
V1 = initial velocity
Biomechanical
Formulae
Your Task!
 Read
pages 230 – 234
 Answer Questions on Handout on course
website