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CHAPTER 4
AN INTRODUCTION TO
BIOMECHANICS
Biomechanics
Biomechanics is the study of how and why the
human body moves.
 It investigates how the physical laws of
mechanics apply to the human body.
 Role of biomechanist: analyse an athletes
performance in order to improve technique,
improve equipment design and reduce injuries.
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– Quantitative Analysis: use of numbers (eg speed /
distance / time)
– Qualitative Analysis: description without numbers (eg
bend your knees
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Checkpoints: Page 95 – Q.1,3
Principles of Biomechanics
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CD-ROM:
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Overview
Inertia
Mass
Force
 Types of forces
– Newtons Laws of Motion
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Velocity: (page 98)
– What does velocity measure?
– What are its two important characteristics?
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Read: Reality PE Snapshots (Page 99)
– Radar equipment!
Principles (cont)
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CD-ROM:
– Impulse
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Checkpoints: (page 102)
– Questions: 1, 2, 4, 5
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Acceleration: (Newton’s 2nd law)
– What is acceleration?
– How do you calculate acceleration?
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Conservation of momentum: (Newtons 3rd law)
– What is this principle?
– Give an example of how this principle works?
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Elasticity:
– What does the term elasticity mean? Explain two ways in which
a tennis player can generate more velocity through elasticity.
Principles (cont)
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Summation of Momentum:
– Define summation of momentum?
– When does effective summation of
momentum take place?
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CD-ROM:
– Friction
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Checkpoints: (page 112)
– Questions 3, 5, 6
Balance and Stability
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Read pages 113-118
Define the terms Balance and Stability?
What factors affect balance and stability?
Explain the difference between static and
dynamic balances?
What is meant by the ‘centre of gravity’ and how
does it change when you change your body
position?
How does the mass of a person affect their
stability?
CD-ROM: Recap of balance using CD examples.
Basic movement patterns
Striking
Throwing
Running
Stopping
Basic movement patterns
Striking
Throwing
Running
Stopping
Tennis
Baseball
Athletics
Baseball
Golf
Basketball
Baseball
Netball
Volleyballl
Netball
Cricket
Athletics
Cricket
Athletics
Soccer
Cycling
Biomechanical principles associated with
basic movement patterns
Striking Golf
Newtons
laws (force)
levers
momentum
impact
stability
Throwing Baseball
projectile
Running Athletics
forces
Stopping Netball
forces
motion
(action/
acceleration
flattening the reaction)
and
arc
motion
deceleration
summation of (straight line) Newtons
momentum
momentum laws
accuracy
friction
friction
Tennis
Biomechanical principles associated
with tennis
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Forces
Levers
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Torque
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Velocity
Power
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Acceleration
Deceleration
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Accuracy
Mass
Inertia
Projectile motion
Momentum
Elasticity
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Motion
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Impulse
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Coefficient of restitution
Spin
Centre of gravity
Base of support
Tennis
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Force (Newtons N)
– A push or a pull
– What effect does a force have on an object?
Starts, stops, speeds up, slows down,
changes direction. It changes an objects
velocity

Velocity (ms-1)
– displacement / time

Mass (kg)
– Amount of matter in an object
– Weight is an indirect measure of mass

Acceleration (ms-2)
- change in velocity / time
- final velocity – initial velocity
time
Newtons laws
1.
A body continues in its state of rest or of
uniform motion in a straight line unless it is
compelled to change that state by forces
acting on it.
2.
The acceleration of an object is directly
proportional to the net force applied and
inversely proportional to its mass.
F = ma
For every action the is an equal and opposite
3.
reaction.
Momentum
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Momentum (kg ms-1)
- p = mv
- two objects travelling at the same
velocity, the one with the greater mass will
have the greater momentum and vice
versa, two objects of the same mass, the
one travelling at a greater velocity will
have a greater momentum.
- momentum is always conserved
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Impulse
– Change in momentum
– I =  p OR I = Ft
– Impulse can be increased by increasing the
force applied or increasing the time over
which the force is applied.
– When a mass is constant, a change in impulse
will result in a greater release velocity of the
object (ball)
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Summation of momentum
– Used to maximise the speed of the racquet
head
– Works when the larger slower body parts
begin the movement and move sequentially
through until the smaller and quicker finish
the movement.
– See laboratory
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Elasticity
– The ability of an object to return to its original
shape
– The more quickly an object does this the less
energy it looses
– Coefficient of restitution is a measure of an
objects elasticity
e = height bounced
height dropped
– String tension determines how much contact
time the ball has with the racquet
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Levers
– Classes of levers
– Factors that affect the use of external levers
 Length of levers
 Inertia of the lever
 Force
Compare and contrast techniques (elite
and novice)
 Evaluate performance using biomechanical
principles
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