TOPIC 8:
BIOMECHANICS AND
SKILLED PERFORMANCE
8.1 Motion
8.2 Speed and Velocity
8.3 Summation of Force, Direction & Impact
8.4 Leverage
8.5 Newton’s Law of Motions
8.6 Centre of Mass, Balance & Stability
8.7 Equilibrium, Static and Dynamic
8.8 Improved Technology and Performance
8.1 Motion
What is Motion?
Motion is to do with movement, and to have movement certain factors must be present
a.
An object must change position, both in time and space
b.
Forces of some description must be applied.
Example: If looking just at the foot of the swimmer (diagram 1) diving into the pool it is evident that there has been a
change in position by the foot, both in space and time.
A reaction force as a result o the swimmer pushing down through the bocks propels the swimmer off the blocks and
through the air towards the water.
Hence motion has occurred, as there was a change in position of the swimmer in space and time (diagram 1) through
the application of a force (diagram 2).
Linear Motion
Liner motion is when all parts of the body describe parallel straight lines.
Question 1:
All parts of the body travel exactly the ……………………………………….. at the same …………… .
Curvilinear Motion
Curvilinear motion is when parts of the body describe parallel curved lines.
Source:
http://photography.nationalgeographic.com/staticfiles/NGS/Shared/StaticFile
s/Photography/Images/Content/blue-waterslide-stanfield-122233-lw.jpg
Source:
http://www.sportindustry.biz/resource/binary/cache/3e0a405167cab8ffd3adb3
85f3e899ff/568x300_bobsleigh_n.jpg
Angular Motion
Angular motion is when a body moves around an axis of rotation. There can be an internal axis and external axis.
Angular motion can also be described as “When a body moved along a rotational pathway so that all parts of the body
travel through the same angle, in the same direction, in the same time.”
Source:
http://www.theage.com.au/ffximage/2006/03/21/cycling2_gallery__47
0x364,0.jpg
Source:
http://images.beijing2008.cn/26/76/Img212017626.jpg
Question 2:
The cyclist has three major internal axis points operating – ca you highlight these on the diagram?
Question 3:
What other types of motion is occurring with the cyclist? ………………………………………………………………………………………………
External axis of Angular Motion
The axis may be outside the body
Source:
http://photos.upi.com/Olympics_2008/549f1eb4464b544e0fde82fee449f855/Womens-Olympic-Gymnastics-Beam-Final-in-Beijing_38.jpg
Internal axis of Angular Motion
The axis may pass through the body, usually at a joint.
Source:
http://nbcsportsmedia.msnbc.com/j/msnbc/Components/Photos/040823/040823_paulHammHighbar_hmed_2p.hmedium.jpg
Question 4:
On the diagram above, mark where the axis of rotation is located.
General (or Combinational) Motion
Projectile Motion
Principles of Projectile Motion – Student Worksheet
Use the vocabulary below to fill in the blanks throughout this worksheet.
You may use each of the words or phrases as many or as few times as you need.
Exercise A: Projectile Motion (Fill in the blanks).
A _____________________ is considered to be any object or body released into the air.
All projectiles have a _____________________ flight path. The flight path of a projectile
is known as the _____________________. The ____________________ of a projectile
consists of a ______________ and _________________ component. The
____________________ component gives the projectile _____________________. The
_________________ component gives the projectile __________________. For example, if
you throw a ball straight up into the air the trajectory has only a _________________
component. When you throw a ball to a friend that is standing 20 metres away from
you the trajectory has a __________________ component as well.
Exercise B: Projectile Motion (Label the diagram below).
horizontal higher initial vertical velocity rough
height length speed of release gravity
parabolic projectile height of release trajectory
less distance initial horizontal velocity vertical
length air resistance angle of release increases
decreases topspin surface to volume ratio backspin
Air pressure poorer
Exercise C: Factors affecting trajectory. (Fill in the blanks)
Regardless of the type of object that is being released, or by what means it is being
projected, the trajectory is affected by the same basic principles. These are:
1. __________________
2. __________________
3. __________________
4. __________________
5. __________________
6. __________________
1._________________ will affect a projectile as it will decrease the height the projectile
can obtain. The force of ________________ acts on the object to pull it back to earth,
limiting the __________________ component of the projectile.
2. As a projectile moves through the air it is slowed down by ____________________.
___________________ will decrease the _________________ component of the trajectory.
The effect of _____________________ is relatively small but needs to be considered. A
badminton shuttle has greater ____________________ than a golf ball as the holes in it
gives it a greater ________________________________. Objects with a ________________
surface will also have increased _____________________________. The speed of a
projectile also affects ________________________ as friction increases with velocity. The
smaller the __________________ of an object, the more air resistance will affect it. This is
evident when considering the difference between throwing a feather and a stone.
Extension: Because air resistance affects the horizontal component of a projectiles
trajectory, the effect of it can be minimized by lowering the _____________________
3. Speed or velocity is directly related to distance. The greater the
___________________________________, the
greater the distance covered in flight.
It is divided into two components:
a) _____________________________________
b) _____________________________________
Having a higher _____________________________
will increase the ________________ of the
trajectory, resulting in a longer flight path. This would be an advantage in sports which
require good height, such as tumbles in gymnastics, high jump and ski jumping (tricks).
Extension: give another example here_________________________________________.
Having a higher ______________________________ will increase the _______________ of
the flight time and therefore the distance covered. This would be an advantage in
sports which primarily require good distance, such as long jump, ski jumping
(distance), and vaults in gymnastics.
Extension: give another example here__________________________________________.
4. The __________________________ changes the relationship between the horizontal
and vertical components of a projectile. The ideal ______________________ is 45
degrees, assuming there is no _____________________ and the take off and landing
points are the same height.
If the _____________________ is greater or less than 45 degrees, the distance covered in
flight will be _____________.
Extension: In sporting situations the angle of release is often lower, around 35 degrees
to 45 degrees. This is because the _________________________ of the body and
because the takeoff point is usually higher than the landing point, e.g., long jump.
5. The higher the ___________________________, the greater the __________________
covered in flight. This is because the higher the projectile is released; the longer it will
be in the air. The ______________________ of the trajectory will be acting on the
projectile for longer. An example of this is throwing a javelin. In javelin, to gain more
______________________ athletes will hold the javelin up _____________________ to
create a greater______________________________.
There is a relationship between height of release and angle of release.
As the height of release__________________, the angle of release ____________________.
As the height of release _________________, the angle of release _____________________.
For example, when shooting, basketball players will have a lot lower angle of release
than shorter basketball players to shoot the ball at the same hoop height.
6. The amount and direction of ___________________ acting on a projectile will directly
affect the _____________________ a projectile will travel. The reason for this is the
________________________ acting on the ball.
Extension example: In a tennis shot, ___________________ gives poorer distance
compared to ___________________. A topspin shot creates a region of high pressure on
top of the ball, and a region of low pressure below. Air moves from a region of high to
low pressure and as a consequence the ball will dip suddenly, decreasing the vertical
component of the trajectory. The opposite is true for backspin.
8.2 Speed and Velocity
DEFINITION

SPEED

Distance covered in a time frame determines the
speed of an object.

VELOCITY
Distance divided by time.

Speed of an object and a direction.
How fast an object is travelling in a certain
directions.
EXAMPLE
100m covered in 10
seconds equates to
10m per sec or
10m/sec or
10ms-1
The runner was
travelling
North East at 10ms-1
Formulas
Distance Travelled (metres)
SPEED
Average Speed =
Time Taken (seconds)
Displacement (metres)
VELOCITY
Average Velocity =
Time Taken (seconds)
Displacement = change in position
Answer the following questions:
a.
What is the average speed of the man running in diagram 8.27? Show calculations.
b.
Now calculate the average velocity. Show calculations.
c.
Calculate the average speed of the following athletes:
Hichmam El Guerrouj
Asafa Powell
Florence Griffith-Joyner
Paula Radcliffe
d.
1500m
100m
100m
42km
3 mins 26 secs
9.77 secs
10.49 secs
2 hrs 15 mins 25 secs
Calculate the velocity of the following example:
“Fred runs 200m in 10 seconds to avoid being attacked by a vicious dog. To get to safety Fred runs
east in a straight line from point A to point B. What is Fred’s average speed and velocity?
Current World Records:
Asafa Powell (Jamaica) 9.77 secs for 100m in Switzerland in 2006
Florence Griffith-Joyner (USA) 10.49 secs for 100m in United States in 1988
8.3 Summation of Force, Direction & Impact
summation of forces: INVOLVE THE INDIVIDUAL FORCES THAT PRODUCE SUCCESSIVE
MOVEMENTS BEING ADDED TOGETHER TO CREATE A LARGER TOTAL FORCE.
FACTORS TO CONSIDER:
 It is important that there is no break in the transfer from one movement to the other.
 Each new movement should begin at the moment the last force ha reached its maximum or the point at
which it begins to fade.
 The final force and velocity of an object depends on the force of the last part of the body.
 Example B indicates more force than example A at the point of contact, the foot is achieving a high level
of force.
 The heavier and stronger parts move first (the upper leg) followed by the smaller and faster body parts
(lower leg and foot).
The trend of body movement is as follows:
Mass (kg)
Trunk
Shoulder or Hip
Upper arm or leg
Lower arm or leg
Hand or Foot
Decreasing
Increasing
Speed (m/sec)
SKILL ACQUISITION & BIOMECHANICS – BIOMECHANICS AND SKILLED PERFORMANCE

Summation of Forces
summation of forces: INVOLVE THE INDIVIDUAL FORCES THAT PRODUCE SUCCESSIVE
MOVEMENTS BEING ADDED TOGETHER TO CREATE A LARGER TOTAL FORCE.
FACTORS TO CONSIDER:
 It is important that there is no break in the transfer from one movement to the other.
 Each new movement should begin at the moment the last force ha reached its maximum or the point at
which it begins to fade.
_________________________________________________________________________________________________
_________________________________________________________________________________________________
_________________________________________________________________________________________________
___________________
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
______________________________
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
______________________________
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
______________________________
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
______________________________
8.4 Leverage


Levers are ‘simple machines’ that make work possible and easier in most cases.
A lever consists of 3 basic components:
EFFORT (or FORCE):
Some degree of effort needs to be applied to ensure
movement. In the human body this effort comes from
contracting muscles and associated tendons.
LOAD (or RESISTANCE or WEIGHT)
Load is the resistance that the effort attempts to
overcome
FULCRUM (or AXIS or PIVOT)
Each lever needs a pivot point to enable the effort and
load arm to rotate.
First Class Lever:
Load
Fulcrum
Examples include
Effort
Seated dumbbell triceps extension
See-saw
Crowbar
Scissors
Second Class Lever:
Standing heel lift
Fulcrum
Examples include
Third Class Lever:
Load
Effort
Nutcracker
Wheelbarrow
Canoe paddle
Fulcrum
Effort
Examples include
Load
Seated bicep curls
Most bodily movements
Shovel
Fishing rod
Force Multiplier & Speed Multiplier:

Speed Multiplier – First and Third Class Levers
Increasing Speed – is generated with longer levers. More speed can be generated if the point of impact
(force) is further away from the fulcrum, therefore the faster speed will create a higher impact causing the
load (a ball) to travel faster and further.
Sporting examples include:
Golf
Baseball
Cricket
Adam Gilchrist holds hit bat further down the grip to extend his bat. However there are laws and rules in all
sports surrounding the length of equipment

Force Multiplier – First and Second Class Levers
Increasing Force: is also generated with longer levers. Moving the fulcrum closer to the load, therefore
extending the effort arm, can generate more force. This will increase the distance the effort arm can be
pushed down.
Tricks to remember the Class of Levers:
Remember the acronym ‘F L E’!
F (fulcrum) is in the middle of a first class lever.
L (load) is in the middle of a second class lever.
E (effort) is in the middle of a third class lever.
8.5 Newton’s Law of Motions
1st Law: Law of Inertia
A body continues in its state of rest (or uniform motion) unle
When things are motionless, they stay that way unless something forces them to move. Similarly, when things are in motion, t
something makes them slow down or stop (drag, friction, a wall etc.). This idea of objects wanting to stay in a state of motion
We know it is harder to get something moving if it has greater mass – it is harder to push a truck than a car. Similarly, it is hard
greater mass – try stopping a Rugby Union player running down the wing. Therefore, the greater the mass, the greater the for
change direction.
2nd Law: Force and Acceleration
A force applied to an object in any particular direction will cause an accelera
the applied force, and inversely proportional to
When a force is applied to an object, provided the force is big enough to overcome the objects inertia, the force will cause the
The path of a kicked football in Australian Rules is curved. It fails to remain in a straight-line once it leaves the boot because o
football which is at rest, and it begins to move. Hence the force (kicking) causes movement, and since it wasn’t moving previo
acceleration.
At the same time, the mass of the object you are trying to move also affects acceleration. A heavier object will accelerate mu
applied.
3rd Law: Action and Reaction
For every given action force there will be an equal a
When a force is applied to an object (I push against a wall with my hands), the thing applying the force will experience the sam
pushes back on my hands with the same force).
Apply this force to a sprint start and you begin to see how the direction of the force is important. As the runner straightens th
turn push the foot upwards. The direction of the reaction force has allowed the runner to move forward and up out of the blo
down, then the movement in the horizontal plane (movement forwards) is zero. If the angle at which they push is directly acro
too great, as the centre of gravity is well forward from the base of support and the runner simply falls over.
8.6 Centre of Mass, Balance & Stability
Centre of Mass: Balance and Stability
Centre of Gravity (or Mass)

Centre of Gravity (or Mass) is a ‘theoretical point’ through which gravity acts on the object.

An object is balanced when the CENTRE OF GRAVITY is located above the objects BASE OF
SUPPORT.

Provided the CENTRE OF GRAVITY is within the BASE OF SUPPORT, the object is balanced.
Centre of
Gravity
Base of
Support
1.
Why doesn’t the following shape fall over?
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
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TOPIC 8: Biomechanics and Skilled Performance
……………………………………………………………………………………………
2.
When an object is lifted to this position, it still fails to
completely tip to the right, why?
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
Stability
For an object to be considered “STABLE” two factors must be present:
1.
The CENTRE OF GRAVITY must be situated over the BASE OF SUPPORT.
2.
Movement of the object must require the CENTRE OF GRAVITY to be raised. The more work
needed, the more stable the object.
For an object to be considered “UNSTABLE” two factors must be present:
1.
2.
When displacement causes the CENTRE OF GRAVITY to be lowered.
The CENTRE OF GRAVITY falls outside the BASE OF SUPPORT.
In relation to CENTRE OF GRAVITY and BASE OF SUPPORT, which of the following three diagrams best
illustrates stability? Rank each glass from least stable to most stable. Explain why using specific
terminology.
15
TOPIC 8: Biomechanics and Skilled Performance
Champagne Glass
Wine Glass
Cocktail Glass
……………………………………………………………………………………………………………………………..……………………………………
……………………………………………………………………………………………………………..……………………………………..………………
…………………………………………………………………………………………..………………………………………………………………………
……………………………………………………………………………..……………………………………………………………………………………
……………………………………………………………..……………………………………………………………………………………………………
…………………………………………..……………………....
8.7 Equilibrium, Static and Dynamic
If forces acting on an object are…
UNBALANCED
BALANCED
Then the object will experience linear or
rotational motion, depending where the
unbalanced force was applied in relation to its
centre of gravity.
Then the object is at rest or in a state of
EQUILIBRIUM.
EQUILIBRIUM depends on:
 The position of the centre of gravity in relation to its base of support.
 The larger the base of support the easier it is to maintain balance.
 Raising the centre of gravity in relation to the base of support results in a less stable position and less
chance of maintaining balance.
 Moving a limb away from the body will drag the centre of gravity towards the limb, making the body
less stable.
STATIC EQUILIBRIUM occurs:
 When a body is static or stationary. e.g. Held positions in gymnastics.
DYNAMIC EQUILIBRIUM occurs:
 When a body is alternating between being balanced and unbalanced.
example, running is an example of dynamic stability as the processes
involves alternating balancing and unbalancing of the body.
 Rotating movement increases the stability of an object.
e.g. spinning top
For
16
TOPIC 8: Biomechanics and Skilled Performance
 Surface friction will influence stability.
e.g. running on ice and sand.
 Additional mass will affect the position of the centre of gravity and impact balance.
QUESTION 1:
When a footballer is about to be bumped by an on coming opponent, they lower their body and lean
towards the oncoming player. Why do these strategies increase the footballer’s chances of remaining on
their feet after the collision?
QUESTION 2:
Explain the advantages of a windsurfer bending his or her knees and lowering the hips rather than
standing up straight when attempting to lift or control the sail?
8.8 Improved Technology and Performance