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# WJEC A2 Biomechanics

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## Geraint Davies

on 10 November 2015

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#### Transcript of WJEC A2 Biomechanics

When levers are put into a diagram they are presented like this;
OCR
Biomechanics

Newtons 3 Laws of Motion
First Law
The law of inertia
An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
Second Law
Law of Acceleration
Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object).
Third Law
Law of Reaction
For every action there is an equal and opposite re-action.
Levers
Levers
Spot the lever
Spot the lever
Spot the lever
Thanks to
Sir Isaac Newton

Sir Isaac Newton was one of the greatest scientists and mathematicians that ever lived. He was born in England on December 25, 1643.
Newton had new ideas about motion, which he called his three laws of motion. He also had ideas about gravity, the diffraction of light, and forces. Newton's ideas were so good that Queen Anne knighted him in 1705. His accomplishments laid the foundations for modern science and revolutionized the world. Sir Isaac Newton died in 1727.
The laws that govern our planet and everything on it
Starter
Draw an image of a sprinter during the start phase of their race and then during the middle phase...
What forces are acting on the body?
How do these forces change during the race?
Planes of Movement
Impulse
Angular Motion
Fluid Mechanics
Watch the video and take any notes you wish to find out more.....
Learning Outcomes
Select a sporting action of your choice and then describe/explain how Newton’s Laws apply.
SOME: Discuss the relationship between each of Newton’s Laws and how this relationship influences sporting actions
MOST: Explain how each of Newton’s laws applies to sporting activity
ALL: Define Newton’s 3 laws of motion; identify an example of the existence of each law
L10
2004
2007
2013
2010
2001
How do Newton's Laws impact on canoeing?
Exam Question - 4 Marks
Force Lines
Lines that help us demonstrate the forces acting on a body and determine what will happen as a result
Putting it all together...
Lesson 12 - Thinking Time
L11
Newton's Laws and Force Lines
The canoe will stay still in the water until the paddle is put in the water and pulled through the water.
The
faster, deeper and stronger
the paddling, the faster the movement of the canoe
in the direction in which the canoe is pulled
(Left side paddling = move to right, right side paddling = move to left, paddling equally on both sides = move straight).
exerts a downwards
and
backwards force
on the water, which exerts an
equal and opposite
forwards and upwards force on the canoe to move it.
Newton’s First Law states that ‘a body will remain at rest or at a constant velocity in a straight line unless acted upon by an external force’. It means that any object that is not accelerating has no net force acting on it – the forces cancel out. This can be applied to any athlete is stationary or maintaining a constant speed in a fixed direction. For example, a 100m sprinter in the middle phase of the race (constant velocity) or in the blocks (stationary).
Newton’s Third Law states that ‘for every action, there is an equal and opposite reaction’. This means that whenever an object exerts a force on another, then it experiences an equal forced exerted back on it in the opposite direction. Reaction forces have many applications within sport including the sprint start, jumping and kicking a ball.

Candidates will use a range of examples and credit should be given for these. It is impossible to cover all sports within the mark scheme.
Newton’s Second Law states that ‘the acceleration of a body is proportional to the force causing it, and the acceleration takes place in the direction that the force acts’. The equation used is Force = mass x acceleration. The most common example used is a sprinter accelerating from his/her blocks.
Zero Net Force = all forces cancel out
So any object is either:
 Stationary or
 Moving at a constant speed and direction as both the horizontal and vertical forces cancel out

shown here as the opposite force lines are the same length
• it does not matter how large the forces are... constant speed means they all cancel out
Newton's 1st Law
Reaction Force
Friction
Weight
Air Resistance
Newton's 2nd Law
Reaction Force
Friction
Weight
Air Resistance
Net force acts upon an object
• net force forward =
acceleration (+ve)
• net force backwards =
deceleration (-ve acceleration)
• net force sideways =
change of direction
force = mass x acceleration F = m x a
• so the bigger the force the bigger the acceleration
• the bigger the mass the smaller the acceleration
Here there is a net force acting forwards as the amount of force applied is greater than the resistance to that force = acceleration
Newton's 3rd Law
Reaction Force
Friction
Weight
Air Resistance
TASK 4: Annotate the swimming picture. What is happening in the picture?
Two bodies exert forces upon each other
Action and reaction are equal and opposite in direction

Action of the jumper? Ground Reaction Force?

The more you push down, the more the ground pushes you up
TASK 5: Now draw and annotate examples of forces!

• Which forces do you need to include?
• What size?
• What effect?

Starter
Have a go at any of the tasks on L12 hand out

They are designed to encourage you 'outside of the box'
Thinkers achieve more!
What do you think?
What do you wonder?
L29
Newton's Laws
Axis of Rotation
Welcome Back to Learning....
Starter
Work with a partner note down how Newton's 3 laws apply to a football being kicked
L12
Now Work as a 4 using flip chart, create a big cartoon poster to show this relationship...
use the cards to label the 3 axis and 3 planes of rotation/movement
Today it is hoped you will learn....
1. What
Newton's 3 Laws of Motion
Are
ALL...
2. An
applied example
for each of Newton's Laws
3. What the
3 axis of rotation
and
3 planes of movement
are
MOST...
1. How Newton's laws can be used in a
variety of sporting contexts
2. How a coach/performer would use knowledge of
planes and axis to influence their practice
SOME...
1. To
evaluate
sporting situations in relation to the planes and axis used, linking to Newton's Laws and
methods of practice
.....
Application
Using the images on page 2, identify and describe how the planes movement and axis of rotation apply to each sporting situation....
The Anatomical Position
Used to describe the human body and its movements...
then complete the table...
Build on it....
Complete the exam question as a method of reflection on today's and previous lessons
By this Friday submit 1st draft Discussion
A lever is a rigid bar that rotates around a fixed point and is used to apply force against a resistance.
Effort
Remember:
the Effort is the point where the
muscle is inserted
(all muscles insert below the joint,
except for the tricep muscle
, which inserts above the joint)
A diagram of a lever in the body;
Levers are classified according to what is in the middle of the lever (fulcrum, effort or resistance)
Three Classifications of Levers

Resistance (weight)

Fulcrum (knee)

Name and sketch the lever operating at the elbow – remember the tricep is the only muscle which inserts above the joint that it works

Resistance (weight)

Fulcrum (elbow)

Effort (tricep insertion point (which is above the elbow))
Task: Think of examples from sport of when a performer goes up on tip toes.
This is one of the few
2nd class levers
in the body.
Always write the words out in full – never use initials
Levers are usually a 3 mark question, marks are awarded for:
Correct terms used in diagram
Correct order of terms in diagram
Lever’s classification correctly identified
It’s what goes in the middle that matters!

Easy cheat:
Extension of the elbow = 1st Class
Plantar-flexion of the ankle = 2nd Class
All other levers = 3rd Class

Exam hints for levers
Effort Arm

Effort Arm
Name and sketch the lever operating at the knee
Effort in the middle = 3rd Class Lever
= 1st class lever
Levers in the body consist of a
muscle
, a

joint
and a
weight
being lifted

Main terms

Joint
- Fulcrum/Pivot

Muscle
- Effort

Weight
- Resistance
Resistance
Fulcrum
Effort
1

2

3
F

R

E
It’s a little rhyme!!!
Take off in high/long jump
Diving off the blocks in swimming
Start of 100m sprint –
These are all 2nd class levers!
Starter
What do these images have in common?
Which is the odd one out??
Name and sketch the lever operating at the ankle
Complete the table by drawing the levers and identifying them....
L16
resistance
Finisher
Mechanical
and
Mechanical
Effort Arm
Distance between the fulcrum and the effort (muscle insertion)
Resistance Arm
Distance between the fulcrum and the resistance
=
=
Resistance Arm
Class of Lever:
3rd
Therefore 3rd class levers have a
long RESISTANCE
arm but a
short EFFORT
arm
Resistance Arm
Effort Arm
Class of Lever:
2nd
Therefore 2nd class levers have a
long EFFORT
arm but a
short RESISTANCE
arm
Resistance Arm
L17
Forces in Flight
A projectile follows a
parabolic curve
when it is in flight
Projectile Motion
The
point of release then......

determine what factors influence how far the projectile travels.

3 factors determine how far a projectile can travel

Motion of a projectile has 2 components:
Components
which can be negligible
it is continually decreasing
E

D

C

B

A

This causes the observed parabolic flight and affects the motion components as follows:
Variations in vertical and horizontal components
Force
is not applied to objects instantaneously.
When we run, our feet are in contact with the ground for a period of time (milliseconds)
time
negative
force
positive
Small negative impulse

Large positive impulse

pos
neg

force

time
Middle of Race
Landing - negative impulse

positive
negative
force

time

End of Race
pos

neg

force

time

Exam Question
Uses familiar terms to linear motion (straight line)
Uses the word angular – meaning rotating or spinning around an axis
Key Terms
Angular momentum
= amount of motion a body has during rotation
Angular velocity
= rate of movement in rotation
Angular acceleration
= the rate of change of velocity
Moment of inertia
= resistance of body to a change of state when rotating

Moment
= force x distance from pivot to line of action of force
Gymnasts try to reduce moment of inertia by tucking up tightly
Moment of inertia is dependent on the
mass of the object
and
how the mass is distributed from the fulcrum
Angular momentum
= amount of motion a body has during rotation (angular velocity x moment of inertia)
A body which is spinning / twisting / tumbling will keep its value of angular momentum once the movement has started
If the
mass moves closer to the axis
of rotation then the
moment of inertia decreases
If the moment of inertia decreases, angular velocity must increase to conserve momentum
Increased angular velocity = increased speed of rotation
DANCER - SPIN JUMP
The movement is initiated with arms held wide - highest possible MI
Once she has taken off, angular momentum is conserved
Flight shape has arms tucked across chest - lowest possible MI
Therefore highest possible rate of spin
To stop spin – arms out to reduce angular velocity and in crease MI

A bit more complicated…..
Exam question

(c)
1 (In air / during flight) angular momentum remains constant (may be shown as straight line on graph);
2 Because there are no net external forces acting;
3 Angular momentum = angular velocity x moment of inertia;
4 A change in moment of inertia results in a change in angular velolcity (may be shown on graph);
5 Tucked somersault has smaller moment of inertia than extended;
6 Hence rotation / angular velocity is quicker in tucked somersault;
7 The problem of somersaulting is the need to complete the movement quickly / lack of time – hence tucked somersault easier to do.
Any 5 for 5 marks

Impulse
Impulse Graph
Start of Race
Impulse
Starter
What lever do you see here
Why is it being used?
Where else might you see it?
nb: if you get bored have a go of TASK 5 or 6!
This means
ground reaction force
is applied over a period of time
Impulse
=
force
x
time
Impulse is also a
change in momentum
(mass x velocity)
Mass stays constant so equates to acceleration
Shown on force-time graphs
Starter
Positive impulse generated from push off
Negative impulse generated as footfall
The
bigger the area
.....
The bigger the
impulse
and the greater the
change of momentum
of the runner......
The greater the
acceleration

What is happening here? Refer to the net impulse and acceleration in your response....
Net impulse is positive – performer is accelerating (but not as fast as in a.
Push-off - positive impulse

What is happening here?
Positive = negative impulses
Zero impulse
No acceleration
Runner at constant velocity

What's happening here?
Net impulse is negative – performer is decelerating
Small positive impulse

Large negative impulse
b.
100m Race
Work through each of the 4 stages of a race.... Note what is happening and what the graph looks like (this one should help!)
In figure a, the area under the force–time curve is
above the horizontal axis
(and hence positive), which means the
force is acting forwards
on the runner. The force lasts for a
relatively long time
, therefore the i
mpulse is high
and positive and would cause large
forward acceleration
and
change of forward velocity
of the runner.
Explanation
AQA June 05 Question 2
(c) (i) As a sprinter accelerates along the track at the beginning of a race, they generate a large impulse. What do you understand by the term ‘impulse’? (2 marks)
(ii) Sketch and label a graph to show the typical impulse generated by the sprinter at this stage of a race (6 marks)
Jun 2005 Question 2
(c)
Impulse is force x time/force applied in unit of time;
Equates to change in momentum;
If mass constant equates to change in acceleration; max of 2 marks

(d) positive clearly larger than negative;
x axis – time;
y axis - force;
units of force shown as Newtons;
units of time shown as milliseconds/less than 1 second
time intersecting at zero on force axes;
positive and negative force axes labelled;
shape of graph - negative and positive components of force shown with negative first;
negative and positive components of force labelled; max of 6 marks
Mark Scheme
L30
Projectiles
A Somersault
Newton's Laws
Conservation of Angular Momentum
Principles of Moments
The Body in Rotation
Re-Starter
Vectors & Scalars
Moments tend to
turn a lever arm
: clockwise or anticlockwise
To keep the lever balanced the clockwise + anticlockwise
forces must be equal
The muscle must generate enough force to
overcome the moment of inertia
(mass x distance from resistance to fulcrum)
The further from the fulcrum, the greater force required to overcome the moment of inertia
Vertical Component is Affected by?
GRAVITY
Horizontal Component is Affected by?
FRICTION
Vertical component
The upward motion of the object
Horizontal component
The horizontal motion of the object
1.
Select a sport where projectiles are used
2.
Consider the technical considerations that must be taken into account by the athlete for effective performance
E.g. Angular velocity or angular momentum
What causes her to spin?
Will she spin forever?
Why?
What questions do you have?
How is she going to stop spinning?
Momentum
Velocity
Acceleration
Force
What happens if she changes shape?
Starter
In your group consider the following:
Draw a graph
of a ball when it is in flight
Explain why
it comes back down to earth in the shape you have drawn
A ball is thrown 25m
from point A to point E
The
further the mass from the fulcrum
, the greater the moment of inertia and therefore the greater the force required to make an
object spin
or
stop spinning
Many sports require performers to attempt the
conservation of angular momentum
and minimize impact of external forces
A rotating body will continue to turn about its axis with constant angular momentum unless an external force acts upon it (Air resistance, friction and gravity)
If Moment of Inertia changes by changing body shape:
Have a go of
Have a go at any of the Exam Q's
What does this mean for a shot putter?
What do gymnasts do the help them spin?
Expert TASK: using the concept of momentum describe each of Newton's 3 laws
1.
2.
A rotating body will accelerate in proportion to the moment of force that is applied and in the direction in which the force is applied
3.
For every action there is an equal and opposite reaction
TASK 6: Note what happens if MI changes by changing body shape
Then angular velocity must also change
to keep angular momentum the same
If MI increases (body spread out more) then angular velocity must decrease (rate of spin gets less)
Jun 2002 Qu 1
(c) Figure 1 shows a diver performing a tucked backward one-and-one–half somersault.

Figure 1

Use figure 1 to explain why performing this dive in a tucked position is easier than performing it in an extended position (5 marks)

Magnus Effect and Bernoulli Principle
L31
L32
Apply what you have learned so far….
PROPERTIES OF FRICTION
friction depends on the force pressing the surfaces together
but not on the area of contact
FRICTION
a ball with back spin will have increased backwards friction with the ground which will cause the ball to bounce backwards form its normal path

As a ball bounces there is friction between the lowest point of the ball and the ground
BOUNCING BALLS WITH SPIN
to make the ball
spin
, it must be hit so that the contact force acts
to one side
of the centre of mass
Before a ball is hit, the predominant force acting is its
weight
- which acts through the
centre of mass
of the ball
SPINNING BALLS - HOW TO MAKE A BALL SPIN
LIFT FORCES
These forces are caused by bulk displacement of fluid and are similar to air resistance when a wing shaped object moves through the air
- discus
- ski jumper
FLIGHT AND LIFT

FLUID FRICTION (or DRAG)
this depends on laminar flow, the smooth flowing of air or water past an object
laminar means flowing in layers streamlining assists laminar flow
FLUID FRICTION
HIGH VALUES OF FLUID FRICTION
any sportsperson or vehicle moving through water will have high values of fluid friction
therefore fluid friction is the critical factor governing swimming speed
FLUID FRICTION
FRICTION
is a force which acts sideways between two surfaces which tend to slide past one another

this force enables sportspeople to accelerate, slow down, swerve, walk, run grip of footwear on floor surface

FRICTION
INERTIA
is the property of mass which means that it is hard to get a massive body moving, and also hard to stop it once it is moving

inertia is related to Newton’s First Law
once an object is moving at constant velocity it will continue to do so until a force acts on it

measured in kilogrammes kg

Using the images below, identify and describe the difference between MASS, WEIGHT and INERTIA
a ball with top spin will have friction driving forwards on the ball - making the ball travel forward of its normal path
back spin - soar
top spin - dip
side spin - slice and hook
soccer free-kicks - swerving
the direction of swerve of spinning ball is therefore in the same sense as the direction of spin
Therefore there is a reduction in pressure on this side of the ball this causes the Magnus effect force as shown
This is the Bernoulli effect applied to spinning (swerving) balls
The Magnus Effect Spin
this causes reduced pressure under the wing and hence a downward force
As layers of air flow past the wing the layers under the wing flow further and therefore faster than those over the top of the wing
FLIGHT - THE BERNOULLI PRINCIPLE
FLUID FRICTION (or DRAG)
when vortices are formed the fluid doesn’t flow smoothly
bits of fluid are flung randomly sideways
which causes drag
because bits of fluid are dragged along with the moving object (cycle helmet)
CROSS SECTIONAL AREA

This is the area of the moving object as viewed from the front
The smaller the better to reduce drag
crouching down, keep elbows in!
HIGH VALUES OF FLUID FRICTION
A cyclist travels much faster than a runner therefore has high fluid friction he or she crouches low to reduce forward cross section
The helmet is designed to minimise turbulent flow
Clothing and wheel profiles are designed to assist streamlining
use of lycra clothing
shape of sports vehicles (cars or bikes)
Wikimedia commons/Frank Steele

FLUID FRICTION FORCE DEPENDS ON:
AIR RESISTANCE or FLUID FRICTION
FLUID FRICTION (or DRAG)
this is a term applying to objects moving through fluids (gases or liquids)
the force acts in the opposite direction to the direction of motion
TASK 2: Explain what technique a mountain biker should use when cycling up hill and why.
PROPERTIES OF FRICTION
friction depends on the force pressing the surfaces together but not on the area of contact

example:
inverted wings on racing cars to increase down force on wheels this increases cornering friction between the wheels and the ground

FRICTION
weight is the predominant force experienced by objects moving freely through air flight of thrown object is a parabola if there is no air resistance

WEIGHT
is produced by the gravitational force field acting on objects or bodies it is a force which acts downwards towards the centre of the Earth

WEIGHT
WEIGHT
and
MASS
are DIFFERENT

- weight is a force produced by the gravitational force field acting on objects or bodies
- it is a force which acts downwards towards the centre of the Earth

MASS

the mass of a body or object is the same everywhere and is related to amount of matter and inertia
MASS - INERTIA
and causes the ball to
spin
this is an
eccentric force
it does not act in the
same line
as the weight

this forms a
couple
which causes a twisting torque on the ball

and creates a lift force
As it moves forward and falls through the air, it pushes aside the air creating a higher pressure underneath the object and a lower pressure over the top of the object
shot or hammer in flight
air resistance much less than weight
therefore angle of release should be around 45o
LOW VALUES OF FLUID FRICTION
low values compared with other forces (fluid friction shown in red in diagrams)
FLUID FRICTION
Fluid Mechanics
Wikimedia commons/MorganaF1

Mass - Weight - Inertia
Friction
Starter
Starter
Please share your homework with someone who was not here last lesson....
What is the difference between
mass
and
weight
?
What is inertia?
Describe the influence of
friction
and
fluid friction
on performance?
The spin takes more layers of air the long way round the ball
This means that the air travels faster round this part of the ball
Complete the blanks using the word bank
TASK 2: In your group bounce a ball with either backspin or top spin
Note:

What does the ball do when it hits the ground?

Why?

How does the Magnus Effect apply here?
if the ball is spinning, this friction can be increased or reduced
Observe the video and note what you learn.....
You are going to share your learning after the video has finished....
Now explain the Bernoulli Principle to your partner
What is meant by the terms
mass
,
inertia
and
momentum
, and their relevance to
sporting performance
‘Everything in the universe is
lazy
; so lazy that
force
is necessary to get it on the move, when
it then travels in a
straight line
with
constant
speed; so lazy that,
once in motion
, further
force
must be applied to slow it down, stop it,
speed it up or change its direction.’
Record thoughts on page 4 of Handout
We can use a ruler to help work out the order....
Even though the examination question may ask you what lever is operating at the
ankle
, the
fulcrum is the joint at the toes
, the
effort the gastrocnemius
causing the plantar-flexion to occur and the
resistance is the weight of the body through the middle of the foot
or
Have a go at
Learning Outcomes
ALL: Define impulse and describe how it relates to momentum and acceleration; Draw accurately force time graphs for a 100m sprint
MOST: Explain the relevance of impulse and force time graphs to sporting performance
SOME: Use impulse and force time graphs in a variety of sporting situations, relating to both momentum and acceleration
Impulse
Have you ever wondered why some people go faster down hill on their bike than you do?!
Why do some people make 'big hits' in rugby?
Why aren't all skiers massive?!
Finisher
Select one of the remaining tasks or go back to...
the
shape
and
size
of the moving object
the
speed
of the moving object
the
streamlining effect
, hence:
body position and shape for swimmer
shape of helmets for cyclists
example:
when riding a mountain bike up a steep hill
you should sit back over the rear wheel
to increase downward force on rear wheel
so that there is more friction between the rear wheel and the ground
any sprinter or game player
air resistance is usually much less than friction effects and weight
therefore streamlining is seen as less important
Body shape, cross section and clothing (surface material to assist laminar flow)
are adjusted to minimise fluid friction
Based on a key principle.....
High Velocity = Low Air Pressure
Low Velocity = High Air Pressure
Full transcript