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OCR A2 Level Physical Education A 7875
OCR Examinations
A Level Physical Education
A 7875
Module 2565 : Option B1
part 1
Biomechanical Analysis of Human Movement
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Module 2565 B1.1.1
INDEX
Index
OCR A2 Level Physical Education A 7875
3
4
5
6
- MECHANICS OF MOTION - LINEAR / ANGULAR MOTION
- FORCE
- FORCE - DEFINITION OF THE NEWTON
- PIN MEN - FREE BODY DIAGRAMS
SHAPE OF BODY / FORCES ACTING
7 - PIN MEN - FREE BODY DIAGRAMS
9 - NEWTON’S LAWS OF MOTION
10 - NEWTON’s FIRST LAW
11 - NEWTON’s FIRST LAW - EXAMPLES / THE EFFECT OF FORCES
12 - NEWTON’S SECOND LAW OF MOTION - FORMULA
13 - NEWTON’S SECOND LAW OF MOTION - THE SPRINTER
14 - NEWTON’s THIRD LAW OF MOTION
15 - NEWTON’s THIRD LAW OF MOTION - APPLICATIONS
16 - DISTANCE - DISPLACEMENT
17 - POSITION
18 - SPEED - VELOCITY - DISTANCE-TIME graph
19 - ACCELERATION - DECELERATION / VELOCITY-TIME GRAPH
20 - VECTORS - A VECTOR / SCALAR
21 - VECTORS - ADDING VECTORS
22 - MASS - INERTIA - WEIGHT and MASS are DIFFERENT
23 - The 100m SPRINT - VELOCITY - TIME GRAPH / THE START
24 - The 100m SPRINT - MIDDLE OF RUN / END OF RUN
25 - MOMENTUM
26 - FORCE
27 - FORCE - PROPERTIES OF FORCE / NET FORCE
28 - FORCE - EXAMPLES - NET FORCES
29 - FORCE
EXAMPLE - NET FORCES - THE HIGH JUMPER AT TAKE OFF
30 - TYPES OF FORCE ACTING ON A SPORT PERFORMER
31 - WEIGHT
32 - WEIGHT AND MASS
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33 - REACTION - REACTION FORCES
34 - REACTION - REACTION FORCES EXAMPLES
35 - REACTION - REACTION FORCES EXAMPLES
36 - REACTION - INTERNAL FORCES
37 - FRICTION
38 - FRICTION - PROPERTIES OF FRICTION
39 - FRICTION
40 - FRICTION - FOOTWEAR AND SURFACE
41 - AIR RESISTANCE / FLUID FRICTION
(or DRAG) / FACTORS AFFECTING
42 - FLUID FRICTION
LOW VALUES OF FLUID FRICTION
43 - FLUID FRICTION
HIGH VALUES OF FLUID FRICTION
44 - FLUID FRICTION
HIGH VALUES OF FLUID FRICTION
45 - FLUID FRICTION - LAMINAR FLOW
46 - UPTHRUST - A FLOTATION FLUID FORCE
Module 2565 B1.1.2
Mechanics of Motion
OCR A2 Level Physical Education A 7875
MECHANICS OF MOTION
linear
MECHANICS of
MOTION
LINEAR MOTION
• motion in a straight line
•
examples : the movement of the
body as a whole in :
– sprinting
– cycling
– swimming
– sports vehicles
•
any motion in which there is no
bulk rotation of the object or body
in motion
– projectiles in flight
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angular
ANGULAR MOTION
• motion in which there is a rotation
of the body :
– tumbling
– diving
– spinning skater
– turning during skiing
– spins and turns in dancing
• or part of the body :
– forearm rotating about the
elbow
– lower leg rotating about the
knee
• any twisting or turning motion
– wheels on a bike or vehicle
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Module 2565 B1.1.3
OCR A2 Level Physical Education A 7875
Newton’s Laws of Motion
FORCE
FORCE
• FORCE is push or pull
•
the unit is the NEWTON (10 N is approx
the weight of 1 kg)
•
force changes the state of motion of
an object
force causes acceleration or
deceleration or change of direction
the more force the bigger the
acceleration
•
•
•
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force changes the shape of an object
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Module 2565 B1.1.4
OCR A2 Level Physical Education A 7875
Newton’s Laws of Motion
FORCE
PROPERTIES OF FORCE
• force has direction and size
(value)
• and is therefore a vector
•
•
DEFINITION OF THE NEWTON
• one newton of force is the
force required :
– to produce an acceleration
of 1 ms-2
– in a mass of 1 kg
when describing a force it is
important to explain where the
force acts (the point of action)
as well as the direction
•
•
•
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this is related to the inertial
property of mass
the more force applied, the
more acceleration produced
see Newton’s second law
Module 2565 B1.1.5
OCR A2 Level Physical Education A 7875
Newton’s Laws of Motion
PIN MEN - FREE BODY DIAGRAMS
SHAPE OF BODY
• should be represented
approximately
DIAGRAM
• shows force in black acting downwards
on the ground
• force in red acting upwards on the
jumper’s foot
FORCES ACTING
• forces are represented by
arrows
• in the direction of the force
• the point of action of the
force should be shown where
the force acts
– at the foot
– on the body
– on the hand
• the length of the arrow
represents the size of the force
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Module 2565 B1.1.6
OCR A2 Level Physical Education A 7875
Newton’s Laws of Motion
PIN MEN - FREE BODY DIAGRAMS
FORCES ACTING
• forces are represented by
arrows
• in the direction of the force
• the point of action of the
force should be shown where
the force acts
– at the foot
– on the body
– on the hand
• the length of the arrow
represents the size of the force
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DIAGRAM
• shows four forces acting
• 2 forces acting up on the foot and down on
the body
•
•
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2 forces acting backwards on the body and
forwards on the foot
longer arrows mean greater force
Module 2565 B1.1.7
OCR A2 Level Physical Education A 7875
Newton’s Laws of Motion
PIN MEN - FREE BODY DIAGRAMS
FORCES ACTING
• forces are represented by
arrows
• in the direction of the force
• the point of action of the
force should be shown where
the force acts
– at the foot
– on the body
– on the hand
• the length of the arrow
represents the size of the force
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DIAGRAM
• shows four forces acting
• 2 forces acting horizontally
• 2 forces acting vertically
• longer arrows mean greater force
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Module 2565 B1.1.8
OCR A2 Level Physical Education A 7875
Newton’s Laws of Motion
NEWTON’S LAWS OF MOTION
2nd LAW
a net force acts
F=ma
- produces
acceleration
1st LAW
zero net force
acts
- constant
velocity
NEWTON'S LAWS
3rd LAW
one body exerts
force on another
- reaction
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Module 2565 B1.1.9
Newton’s Laws of motion
OCR A2 Level Physical Education A 7875
NEWTON’s FIRST LAW
NEWTON’S FIRST LAW
• this law is used when zero net force is
applied to an object
• this doesn’t mean that zero force acts,
but that all forces must cancel out
•
with zero net force an object
– is stationary or
– moves at constant speed in the
same direction
•
for the sprinter, horizontal forces cancel
out
•
and vertical forces cancel out
•
hence he / she travels at constant speed
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Module 2565 B1.1.10
Newton’s Laws of motion
OCR A2 Level Physical Education A 7875
NEWTON’s FIRST LAW
NEWTON’S FIRST LAW
• examples :
– a sprinter running at constant speed
– a cyclist going at constant speed
– a swimmer swimming at constant speed
– any vehicle going at constant speed
– any sportsperson standing still
THE EFFECT OF FORCES
• this law does not mean that there are no
forces
• very large forces can act
• but if the object is going at constant
speed
• these forces MUST cancel out
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Module 2565 B1.1.11
Newton’s Laws of Motion
OCR A2 Level Physical Education A 7875
NEWTON’S SECOND LAW OF MOTION
NEWTON’S SECOND LAW
• this law is used when a NET FORCE acts
on an object
• net force forwards produces acceleration
- positive
• net force backwards produces
deceleration - negative
• net force sideways produces change of
direction
FORMULA
• force = mass x acceleration
•
F = m x a
•
•
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hence the bigger the force the bigger
the acceleration
the bigger the mass, the smaller the
acceleration
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Module 2565 B1.1.12
Newton’s Laws of Motion
OCR A2 Level Physical Education A 7875
NEWTON’S SECOND LAW OF MOTION
THE SPRINTER
• four forces are acting
• upwards force = downwards force
•
•
•
backwards force is bigger than
forwards force
•
therefore there is a net backwards
force
producing a negative acceleration
or deceleration
•
•
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therefore there is no upward
acceleration
the sprinter runs horizontally
Module 2565 B1.1.13
Newton’s Laws of motion
OCR A2 Level Physical Education A 7875
NEWTON’s THIRD LAW OF MOTION
NEWTON’S THIRD LAW
• this law is used when two bodies exert
forces on one another
• action and reaction are equal and
opposite in direction
•
action of jumper down on ground
(force in black)
•
= reaction of ground up on jumper
(force in red)
•
the harder you push down on the ground,
the more the ground pushes up on you
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Module 2565 B1.1.14
Newton’s Laws of motion
OCR A2 Level Physical Education A 7875
NEWTON’s THIRD LAW OF MOTION
APPLICATIONS
• at the sprint start - the athlete pushes back on
the blocks as hard as possible
• the blocks push forward - and provides
forward acceleration - on the athlete
•
a swimmer drives backwards on water with
hands and feet (force in black)
•
the water pushes the swimmer forward
(force in red)
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Module 2565 B1.1.15
Linear Motion - Measurements
OCR A2 Level Physical Education A 7875
DISTANCE - DISPLACEMENT
DISTANCE
• means the total path length moved
by a body
• example :
– a 10,000 m race is run round and
round the track
– 25 times 400 m, starting and
finishing POSITION are the same
– distance travelled is 10,000 m
• unit the metre m
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DISPLACEMENT
• this means the vector distance from a
fixed point (starting point or origin)
• the actual ‘as the crow flies’ distance
between start and finish (with direction
included)
• example :
– the start and finish of a long
distance race (Stage 5 of the Tours
de France)
– may be 190 km apart due West,
but the distance travelled may be
250 km!
• unit the metre m
Module 2565 B1.1.16
Linear Motion - Measurements
OCR A2 Level Physical Education A 7875
POSITION
POSITION
• a way of explaining where a point is relative to some
fixed point
•
position is usually expressed in terms of coordinates (x
and y) like a graph in maths
•
example :
– the centre forward takes a shot from a position 20
m out from the goal line, and 10m to the left of the
left hand post
– the left hand post is the fixed point or origin of
measurement
– 20 m and 10 m are the coordinates of the position
of the centre forward relative to that point.
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Module 2565 B1.1.17
Linear Motion - Measurements
OCR A2 Level Physical Education A 7875
SPEED - VELOCITY
SPEED
• = distance moved v = s
time taken
t
• = scalar (no direction)
unit ms-1
VELOCITY
• = speed in a given direction
• = vector
DISTANCE / TIME graph
• gradient of graph is velocity
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Module 2565 B1.1.18
Linear Motion - Measurements
OCR A2 Level Physical Education A 7875
ACCELERATION
ACCELERATION
• = change of velocity
time taken to change
a=v-u
t
unit ms-2
•
•
•
acceleration is in the same direction as net force
acceleration is a vector (has direction)
an object changing direction is accelerating, since the velocity
changes
• example :
– swerving rugby player
– direction of acceleration is along the radius of the curve
(path of player)
– this is a radial acceleration
DECELERATION
• is negative acceleration (slowing down)
VELOCITY / TIME graph
• gradient of graph is acceleration
• area under graph is distance travelled
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Module 2565 B1.1.19
Linear Motion - Measurements
OCR A2 Level Physical Education A 7875
VECTORS
A VECTOR
• has direction as well as size (magnitude or value)
•
•
•
•
a vector can be represented by a line on
a piece of paper (graph paper)
the length of the line represents the size
(say the value of a force in newtons)
the angle of the line to the horizontal
represents the direction
examples of vectors are :
– force, acceleration, velocity, weight,
momentum
A SCALAR
• has size (value) only
• examples of scalars are :
– mass, temperature, energy, speed, distance, volume,
pressure, power.
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Module 2565 B1.1.20
Linear Motion - Measurements
VECTORS
OCR A2 Level Physical Education A 7875
ADDING VECTORS
• is a process which involves finding the
size and direction of a resultant of 2
or more vectors
•
complete the parallelogram as
shown in the example
•
the resultant is the diagonal of the
parallelogram
•
the resultant of two vectors at right
angles
is found by completing the
rectangle
•
•

F2 = F12 + F22
q = tan-1(F2/F1)
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Module 2565 B1.1.21
Linear Motion - Measurements
OCR A2 Level Physical Education A 7875
MASS - INERTIA
MASS
• the mass of a body or object is the
same everywhere and is related to
amount of matter and inertia
WEIGHT and MASS are DIFFERENT
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
•
•
•
weight is produced by the
gravitational force field acting on
objects / bodies
it is a force which acts downwards
towards the centre of the Earth
measured in kilogrammes kg
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Module 2565 B1.1.22
Linear Motion - Measurements
The 100m SPRINT
OCR A2 Level Physical Education A 7875
VELOCITY - TIME GRAPH
• steep slope for first part = large
acceleration
• this corresponds with a large forward
net force applied at the start
THE START
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•
•
friction is large
provides forward acceleration
•
net force forwards (resultant) shown
in black
Module 2565 B1.1.23
Linear Motion - Measurements
The 100m SPRINT
OCR A2 Level Physical Education A 7875
MIDDLE OF RUN
• the velocity time graph is almost level
• which means that acceleration is almost
zero
• therefore forces cancel out
END OF RUN
• the velocity time graph has a small negative
slope
• which means that the sprinter decelerates
• therefore there is a net force backwards
shown in black
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Module 2565 B1.1.24
Linear Motion - Momentum
OCR A2 Level Physical Education A 7875
MOMENTUM
MOMENTUM
• a concept derived from Newton's second
law which says :
• force = rate of change of momentum
•
•
•
(Linear) momentum = mass x velocity
linear means in a straight line
momentum includes both mass and velocity
•
so an object which has a lot of momentum
requires a lot of force to stop it
which is a good argument for fast heavy
rugby players or American footballers
•
•
momentum is a vector (and therefore has
direction)
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Module 2565 B1.1.25
Force
FORCE
OCR A2 Level Physical Education A 7875
FORCE
• FORCE is push or pull
•
the unit is the NEWTON (10 N is approx the weight of 1 kg)
•
•
•
force changes the state of motion of an object
force causes acceleration or deceleration or change of direction
the more force the bigger the acceleration
•
force changes the shape of an object
DEFINITION OF THE NEWTON
• one newton of force is the force required :
– to produce an acceleration of 1 ms-2
– in a mass of 1 kg
•
•
•
this is related to the inertial property of mass
the more force applied, the more acceleration produced
see Newton’s second law, F = m x a
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Module 2565 B1.1.26
OCR A2 Level Physical Education A 7875
Force
FORCE
PROPERTIES OF FORCE
• force has direction and size (value)
• and is therefore a VECTOR
•
•
when describing a force it is important to explain
where the force acts (the point of action)
as well as the direction
NET FORCE
• net force is the result of all forces
added together taking the direction into
account (see VECTORS)
•
•
•
net force forwards produces
acceleration - positive
net force backwards produces
deceleration - negative
net force sideways produces change
of direction
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Module 2565 B1.1.27
Force
FORCE
OCR A2 Level Physical Education A 7875
EXAMPLES - NET FORCES
• sprinter accelerating
• jumper taking off
• projectile in flight
• jumper landing
– as feet make contact with ground
– net force backwards causes deceleration
EXAMPLES - ZERO NET FORCE
• sprinter at full speed
• swimmer at full speed
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Module 2565 B1.1.28
Force
FORCE
OCR A2 Level Physical Education A 7875
EXAMPLE - NET FORCES - THE HIGH JUMPER AT
TAKE OFF
• the net force is made up from a number of forces
which add together
• in the case of the high jumper taking off the following
forces act :
•
his weight (acting downwards)
•
the reaction force acting upwards
•
and a friction force acting backwards
•
these forces add up to a net force as shown
•
•
which will cause upward acceleration - for take-off
and forward rotation (over the bar)
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Module 2565 B1.1.29
Types of Force
OCR A2 Level Physical Education A 7875
TYPES OF FORCE ACTING ON A SPORT PERFORMER
WEIGHT
MAGNUS EFFECT
REACTION
TYPE OF FORCE
AIR RESISTANCE
FLUID FRICTION
FRICTION
UPTHRUST
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Module 2565 B1.1.30
Types of Force - Weight
WEIGHT
OCR A2 Level Physical Education A 7875
WEIGHT
• is produced by the gravitational force
field acting on objects / bodies
• it is a force which acts downwards
towards the centre of the Earth
•
•
•
•
•
weight is the predominant force
experienced by objects moving freely
through air
flight of thrown object is a parabola if
no air resistance
your weight would be approximately the
same everywhere on the Earth’s
surface
value g = the gravitational field
strength = 10 Newtons per kilogramme
variations occur between poles and
equator, and at altitude
– less weight at altitude means slightly
further jumps and throws
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Module 2565 B1.1.31
Types of Force - Weight
OCR A2 Level Physical Education A 7875
WEIGHT AND MASS
WEIGHT and MASS are DIFFERENT
WEIGHT
• is a force
• depends on gravity
– therefore zero in outer space
– one sixth of Earth value on the
moon
• measured in newtons N
• calculated using W = m x g
• g = 10 newtons per kg mass
MASS
• mass is the same everywhere in
the universe regardless of gravity
• and is related to amount of matter
• and inertia
• inertia is the property of mass which
means that it is
– hard to get a massive body
moving
– also hard to stop it once it is
moving
•
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measured in kilogrammes kg
Module 2565 B1.1.32
Types of Force - Reaction
OCR A2 Level Physical Education A 7875
REACTION
REACTION FORCES
• are forces acting via Newton’s Third Law
•
when one object pushes on another, the first object experiences
a force equal but opposite in direction to the second
•
jumper pushes down on the ground,
ground pushes up on the jumper
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•
weight lifter pulls up on weight,
weight pulls down on lifter
Module 2565 B1.1.33
Types of Force - Reaction
OCR A2 Level Physical Education A 7875
REACTION
REACTION FORCES
• swimmer pushes
backwards on the water
•
reaction force thrusts the
swimmer forward
•
canoeist pushes
backwards on the water
•
reaction force thrusts the
canoe forward
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Module 2565 B1.1.34
Types of Force - Reaction
OCR A2 Level Physical Education A 7875
REACTION
REACTION FORCES
• sprinter pushes back and down
on the ground
•
the ground pushes upwards and
forwards on the sprinter
REACTION FORCES
• in cycling, the tyre on the rear
wheel pushes backward on the
ground
•
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the ground pushes forward on
the rear wheel
Module 2565 B1.1.35
Types of Force - Reaction
OCR A2 Level Physical Education A 7875
REACTION
INTERNAL FORCES
• are exerted on both origin and insertion of
a muscle.
• the force on the insertion is a reaction to
the force on the origin
•
•
•
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force on origin pulls bone H to the right
force on insertion pulls bone U to the left
the two forces are equal in size but
opposite in direction
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Module 2565 B1.1.36
Types of Force - Friction
OCR A2 Level Physical Education A 7875
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 acts forwards on the feet of an
accelerating runner
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Module 2565 B1.1.37
Types of Force - Friction
OCR A2 Level Physical Education A 7875
FRICTION
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
•
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
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Module 2565 B1.1.38
Types of Force - Friction
OCR A2 Level Physical Education A 7875
FRICTION
FRICTION
• enables swerving by games players
– rugby
– soccer
– hockey
– tennis
•
•
the friction force then acts
sideways to the direction of motion
and changes the direction of
motion
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Module 2565 B1.1.39
Types of Force - Friction
OCR A2 Level Physical Education A 7875
FRICTION
FOOTWEAR AND SURFACE
• studs, spikes increase friction to enable better
swerving and accelerating and decelerating in games
or track situations
• this applies to soft or wet surfaces
•
•
for dry hard surfaces
solid smooth rubber soles can give better friction
– discus / hammer shoes
– rock climbing shoes
– tennis shoes for concrete surfaces
•
in snow and ice, long slender footwear (skates /
skis)
– forward friction is low
– sideways friction is high
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Module 2565 B1.1.40
OCR A2 Level Physical Education A 7875
Types of Force - Air-resistance / Fluid Friction
AIR RESISTANCE / 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
FLUID FRICTION FORCE DEPENDS ON
• 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
– use of lycra clothing
– shape of sports vehicles (cars /
bikes)
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shape
size
FLUID FRICTION
speed
streamlining
Module 2565 B1.1.41
OCR A2 Level Physical Education A 7875
Types of Force - Air-resistance / Fluid Friction
FLUID FRICTION
LOW VALUES OF FLUID FRICTION
• low values compared with other forces
•
•
•
•
•
•
any sprinter or game player
air resistance is usually much less
than friction effects and weight
therefore streamlining is seen as less
important
shot / hammer in flight
air resistance much less than weight
therefore angle of release should be
around 45o
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Module 2565 B1.1.42
OCR A2 Level Physical Education A 7875
Types of Force - Air-resistance / Fluid Friction
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
•
•
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body shape / cross section and clothing
(surface material to assist laminar flow)
are adjusted to minimise fluid friction
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Module 2565 B1.1.43
OCR A2 Level Physical Education A 7875
Types of Force - Air-resistance / Fluid Friction
FLUID FRICTION
HIGH VALUES OF FLUID FRICTION
• a cyclist travels much faster than a runner therefore has
high fluid friction
• he / she crouches low to reduce forward cross section
• the helmet is designed to minimise turbulent flow
• clothing / wheel profile are designed to assist
streamlining
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Module 2565 B1.1.44
OCR A2 Level Physical Education A 7875
Types of Force - Air-resistance / Fluid Friction
FLUID FRICTION
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
•
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)
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Module 2565 B1.1.45
OCR A2 Level Physical Education A 7875
Types of Force
UPTHRUST - A FLOTATION FLUID FORCE
UPTHRUST
• is a force acting upwards on any object immersed or
partially immersed in water (or any fluid)
• this is the force which enables objects to float
•
•
•
it is caused by displacement of fluid
the fluid is pushed aside by the floating object
the fluid (as a reaction force) pushes upwards on
the floating object
•
all swimmers and sports boats experience this force
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Module 2565 B1.1.46