Biomechanics
The study of forces and their effects on the human body
Year 11
Achievement Standard 1.2
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Linear motion
Motion that occurs is a straight line. All parts of the body
move in the same direction and at the same speed (e.g.
jumping up in the air to catch a ball or travelling in a car).
Line out jumper in Rugby Union
Drag Racing
Characteristics of motion
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Angular motion
Motion that occurs around an axis. This axis can be
internal (e.g. body parts rotating around a joint) or
external (e.g. spinning a ball on your finger).
Spinning a ball on your finger
Spinning figure skater
Characteristics of motion
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General Motion
A combination of linear and angular motion. This is the
most common of all movements, as most human
movement requires the rotation of body parts around joints
(e.g. cycling, swimming and running).
Characteristics of motion
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1.
2.
3.
4.
5.
6.
Apply your knowledge!
Classify the following physical activities as linear motion or
angular motion or general motion.
Sprinting
Rebounding a basketball
Driving a car
Tossing a underhand ball in basketball
Horse riding
Lawn bowls
Characteristics of motion

Centre of gravity can be defined as “the
single point at which all parts of an object are
equally balanced”.

For a ‘normal’ human being standing upright, their centre of
gravity lies around the area of their navel.

A persons centre of gravity can change depending on their
body position because as mentioned before, the centre of
gravity is the exact point where all parts of an object are
equally balanced.

The centre of gravity can also lie outside an object, especially
if the object is bent over or leaning in a certain direction
Centre of gravity
Centre of gravity for a “normal person”
= Centre of gravity
Centre of gravity
Centre of gravity for a person whose hands a stretched in the
air
= Centre of gravity
Centre of gravity
Centre of gravity outside of a persons body
= Centre of gravity
Centre of gravity

Line of gravity is the vertical line that passes
through the centre of gravity to the ground.

If the line of gravity falls within the object’s base of support
(i.e. its contact with the ground), the object is relatively
stable.

If the line of gravity falls outside the object’s base of
support (i.e. its contact with the ground), the object is
relatively unstable.
Line of gravity
- The line of gravity is important
when determining the stability of an object.
Line of gravity
Line of gravity
Centre of
gravity
Centre of
gravity
STABLE
Line of gravity
UNSTABLE

BOS is the area within an objects point of contact with the
ground. The larger the area the base of support covers,
the more stable an object will be.
Wide BOS
BOS
Base of support –
Narrow BOS
BOS
The object on the left is
more stable because of its relatively larger BOS

The line of gravity (LOG) must go outside the base of support to initiate or continue
movement.

The direction that the line of gravity takes relative to the BOS will be the direction of
the resulting movement.

The further away the LOG is from the BOS, the greater the tendency the body has to
move in that direction. E.g. Evasive running.
Line of gravity
Top of body moves
towards LOG
Direction of movement
Leg pushes against the ground
Base of support
Line of gravity, BOS in relation to movement
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Apply your knowledge!
Label the following images with the COG, LOG and BOS.
Is the performer stable?
Centre of gravity, Line of gravity, Base
of support and Physical activity
1. Name 3 ways to ensure you are stable (use
biomechanical terms)
2. In relation to stability, what is one
advantage of being shorter? (use
biomechanical terms)
3. When you do a right handed lay up, what
movement is occurring at your right hip?
4. What is the agonist muscle causing this
movement?
5. What is the antagonist muscle during this
movement?
5 Quick Questions

What is a force?
◦ A push, pull or twist that causes movement of
an object
◦ Force = Mass x Acceleration
◦ Levers are used to apply a force
Force

Consist of a pivot point (fulcrum) and a lever arm
(connecting the pivot point to the resistance).
Downward Pressure
Resistance
Fulcrum (pivot point)
Lever arm
Levers – are used to apply force

The amount of leverage a person processes is dependent
on the length of their body, in particular the length of
their arms and legs.

Longer levers result in greater speed at the end of the
lever arms – this is beneficial for throwing and striking
objects.

Short levers can be moved with less force and at greater
speeds – this is beneficial for moving body parts quickly
and applying strength for pushing, pulling and lifting
objects.

Question: From this information, what can you assume
about a shorter person in comparison to a taller person?
Levers

In the human body, levers are made up of the joints
(fulcrum) and the bones that connect them to the objects
being moved.

Levers in the human body can be manipulated to improve
speed and apply large forces at the same time

Example: Running – lifting your foot and knee up will
create a shorter lever, therefore you can run faster
Using Levers in Sport

When exploring the area of biomechanics
and human movement, it is useful to look
at motion through the observations made
by Sir Isaac Newton.

Newton was a famous seventeenthcentury scientist who developed the three
laws that govern all motion.
Newton’s Laws
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‘A body continues in its state of rest
or uniform motion unless an
unbalanced force acts upon it.’
In other words, a body will remain at rest or in motion
unless acted upon by a force. In order to get a body
moving, a force must overcome the body’s tendency to
remain at rest or inertia. The amount of inertia a body
has depends on its mass.
Newton’s 1st Law – The law of
inertia.

This soccer ball will remain at rest, until a
force acts on it
Newton’s 1st Law – The law of inertia
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‘The acceleration of an object is directly
proportional to the force causing it, is in the
same direction as the force, and is inversely
proportional to the mass of the object’.
When a force is applied to an object it will move in the direction
the force was applied, and, depending on the size of the force
and the size of the object, the object will accelerate accordingly.
A smaller object will move faster than a larger object.
 A greater force will move an object faster than a smaller force.
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Newton’s 2nd Law – Mass, force & acceleration
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Classroom experiment

Using the equipment you have been
given, answer the questions in the
workbook as a group
Newton’s 2nd Law – mass, force & acceleration

‘Whenever a force is applied there is
an equal and opposite reaction.’

If an athlete exerts a force onto the ground in order to
push off, the ground will exert an equal and opposite force
on the athlete, pushing them up into the air.

The first force of the athlete pushing into the ground is
called an action force. The second force is called the
reaction force (when the second body applies an opposing
force back).
Newton’s 3rd Law – action & reaction
Newton’s 3rd Law – action & reaction

To give an object momentum in activities such as throwing,
kicking or striking an object, the amount of momentum
given to the object is determined by ‘the sum of all forces
generated by each body part’ (i.e. Force summation).

To gain maximum momentum, the force needs to be
generated by:
1.
2.
3.
4.
Using as many segments of the body as possible.
In the correct sequence, using large muscles first
and then the smallest muscles last but fastest.
With correct timing.
Through the greatest range of motion.
Force summation

In order to maximise power and efficiency of the
shot, the whole body is used.

Your body does not move all at once.

The shot begins with the movement of the legs,
pushing into the ground.

The force is then returned back up the legs, up
to the shoulders, down the forearms right to the
release of the ball at the fingertips.
Application of force summation – free-throw
shot technique
Application of force summation – free-throw
shot technique

As soon as an object is thrown it becomes a
projectile.

A projectile is influenced by the principles that
govern projectile motion – gravity, air resistance,
speed height, and angle of release.
Projectile motion
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Different angles of release affect the distance travelled and the height
attained by an object.

When a ball is released from ground level, the optimal angle for release
for maximum distance is about 45 degrees
Angle of release
90 degrees
45 degrees
0 degrees

The height of release is important when propelling an object anywhere
higher than ground level. If an object needs to clear something higher
than ground level (e.g. The cross bar on a goal post), the angle needs to
be greater then 45 degrees.
Speed, height & angle of release
The height an object is released with
determine the distance the object travels
 e.g.

Height of release