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Biomechanics
The study of cause and effect
FORM 6 PED
Why study Biomechanics?
 To understand how people can move.
1. To enhance skill performance
 elite athletes
 physical challenges
Why study Biomechanics?
2. To lower the risk for injury
 Exercise equipment & technique
 shoes & surfaces
 braces & orthotics
 Automobiles
 collisions
Why study Biomechanics?
Can a
cow
really
jump
over the
moon?
Define a Force
1. Forces and Levers
A force is a push or pull.
When a force acts upon a body (object) it can
produce 3 types of movement.
 Translation – Moves from A to B.
e.g. A golf shot starts on the tee and finishes
on the fairway.
 Rotation – If force not applied through the centre
of gravity the object will rotate e.g. putting spin
on a volleyball serve.
 Deformation – The object loses shape on
impact e.g. a squash ball being hit
The main force acting on all parts of the body is gravity.
Centre of gravity (COG) can therefore be defined as the
point at which all parts of the body are in balance.
In men, the COG is about 57% of standing height, in
women 55%. Women have more mass concentrated
around the hips and below and this gives them an
advantage in balance related activities.
When we produce rotation as a consequence of a force
being applied, the body rotates about the COG.
These are known as the AXIS OF ROTATION
The body rotates around
three different axes.
1. Longitudinal
E.g. Pirouette in
dance, twist in
diving, spinning in
ice skating
2. Transverse
e.g. forward / backward
roll/ somersault
3. Sagital
e.g. cartwheel, cricket
delivery,
Levers

A lever is basically a rigid structure, hinged at
some part and to which forces are applied at
two other points.

1.
2.
3.
Levers consists of three parts.
Resistance
Effort
Falcrum or pivot
The point of support, or axis, about which a lever
may be made to rotate
FUNCTIONS OF A LEVER
Levers perform two main functions:
1. To increase the resistance that can be moved
with a given effort, eg. Crowbar.
2. To increase the velocity at which an object
will move with a given force, eg. Golf club
There are three classes of lever.
Levers-First Class
 In a first class lever
the fulcrum is in the
middle and the load
and effort is on either
side
 Think of a see-saw
Levers-Second Class
 In a second class
lever the fulcrum is at
the end, with the load
in the middle
 Think of a
wheelbarrow
Levers-Third Class
 In a third class lever
the fulcrum is again
at the end, but the
effort is in the middle
 Think of a pair of
tweezers
Newton’s Laws of Motion
Sir Isaac Newton (16421727) developed 3 laws
to explain relationship
between the forces
acting on a body and the
motion of a body.
Law 1
“An object at rest
tends to remain at
rest unless acted
upon by some
external force”
This is known as
Inertia. High level of
inertia can be
advantageous and
disadvantageous in
different sports.
Law 2
“When a force acts upon a
mass, the result is
acceleration of that mass”
 The greater the force, the
greater the acceleration
 The smaller the mass, the
greater the acceleration
 The mass will accelerate in the
direction the force is applied
Force = mass x acceleration
(F=MA)
Law 3
“For every action,
there is an equal
and opposite
reaction”
These 2 forces always
work in pairs
1. action force
2. reaction force
The big question..
Analysing the Overhead Serve
in Volleyball
Try analysing the volleyball serve.
Ask yourself “ How is the biomechanical
principle – Newton’s Laws of Motion
being applied to the overhead serve
in volleyball? Where can I see this
being applied?
This will help you to explain how they
contribute to the performance of the
serve.
Principles of Balance and
Stability
Stability
Stability is defined as the ability to hold or
maintain a position in space.
Stability
The two main elements in maintaining stability
are:
1. The position of the COG with respect to the
base of support.
2. The direction of the forces involved.
Principle 1
The closer the line of gravity is to the
centre of the base of support, the greater
the probability of maintaining balance.
Principle 2
The broader the base of
support, the greater
the probability of
maintaining balance.
Principle 3
The probability of
maintaining balance
is increased when
the COG is lowered
in relation to the
base of support.
Principle 4
The further the body part moves
away from the line of gravity, the
probability of maintaining
balance decreases unless
another body part moves to
compensate for it.
Types of Motion
There are 4 main types of motion;
A) Linear Motion
When parts of the
body move in
straight parallel
lines. Quite rare in
sporting situations.
e.g. tobogganing down
a hill, dropping a
ball, sliding into first
base
B) Curvilinear Motion
When points in the
body move in curved
parallel lines.
e.g. free fall skydiving,
path of an arrow
If the path of two points on a body follow straight parallel
lines, the motion is linear. If the path is curved, the motion
is curvilinear.
C) Angular Motion
Rotation about an axis that can be
internal (axis inside the body) or external
(axis outside the body). E.g. swinging on
a high bar, a forward roll, hammer
throwing, pole vault over bar, softball
pitch, fosbury flop.
D) General Motion
Linear motion of the
body as a result of
angular motion of
other parts of the
body.
e.g. cycling,
swimming, using a
wheelchair
Torque ?
Torque is a turning force.
Eccentric force produces spin.
It depends on how far the mass is
from the axis and the size of the
mass.
How do we produce topspin or
backspin ?
Where do we hit the ball ?
How can we generate more spin ?
Momentum
Momentum is moving inertia. We can rewrite
Newton’s 1st law to include momentum.
“An object that is moving will continue to move in
the direction the force was applied until another
force is applied”
The greater the momentum the greater the force
required to stop it e.g. small /large snowball.
Momentum (kgms) = mass (kg) x velocity (ms)
 Momentum can act when an object is
translating. This is linear momentum.
 Momentum can act on an object when it
is rotating. This is angular momentum.
Conservation of
Momentum
When objects collide, momentum is
conserved throughout.
Momentum before impact = momentum after
impact.
MOMENTUM = MASS X VELOCITY
kgms
kg
ms
Use the information on Conservation of Momentum and steps below to
calculate the speed of the golf ball after impact.
A golfer swings a 0.35kg club at 30m/s to hit a 0.004kg golf ball off the tee.
After impact his club speed drops to 25m/s.
Remember
Momentum before impact = Momentum after impact. (M = m x v)
Club Momentum
Ball Momentum
Total Momentum
Ball Momentum
Total Momentum
Before Impact
Club Momentum
After Impact
What is the Ball Velocity?
Momentum = mass x velocity
Velocity = momentum
mass
Use the information on Conservation of Momentum and steps below to
calculate the speed of the hockey stick after impact.
A ice hockey player uses their stick to strike a 500 gram (0.5kg) puck
moving at 2m/s toward their opponent’s goal. The stick has a mass of
2kg and possesses stick head velocity of 25m/s before impact. After
impact, the stick head velocity decreases to 17m/s.
Remember
Momentum before impact = Momentum after impact. (M = m x v)
Stick Momentum
Puck Momentum
Total Momentum
Puck Momentum
Total Momentum
Before Impact
Stick Momentum
After Impact