ocr examinations a level physical education a 7875 module 2565 : option b1 part 1

Module 2565 B1.1.1

OCR A2 Level Physical Education A 7875

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OCR ExaminationsA Level Physical Education

A 7875

Module 2565 : Option B1part 1

Biomechanical Analysis of Human Movement

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INDEX33 - REACTION - REACTION FORCES 34 - REACTION - REACTION FORCES EXAMPLES35 - REACTION - REACTION FORCES EXAMPLES36 - REACTION - INTERNAL FORCES37 - FRICTION38 - FRICTION - PROPERTIES OF FRICTION39 - FRICTION40 - FRICTION - FOOTWEAR AND SURFACE41 - AIR RESISTANCE / FLUID FRICTION (or DRAG) / FACTORS AFFECTING 42 - FLUID FRICTION LOW VALUES OF FLUID FRICTION43 - FLUID FRICTION HIGH VALUES OF FLUID FRICTION44 - FLUID FRICTION HIGH VALUES OF FLUID FRICTION 45 - FLUID FRICTION - LAMINAR FLOW 46 - UPTHRUST - A FLOTATION FLUID FORCE

Index

3 - MECHANICS OF MOTION - LINEAR / ANGULAR MOTION4 - FORCE5 - FORCE - DEFINITION OF THE NEWTON6 - PIN MEN - FREE BODY DIAGRAMS

SHAPE OF BODY / FORCES ACTING7 - PIN MEN - FREE BODY DIAGRAMS9 - NEWTON’S LAWS OF MOTION10 - NEWTON’s FIRST LAW11 - NEWTON’s FIRST LAW - EXAMPLES / THE EFFECT OF

FORCES12 - NEWTON’S SECOND LAW OF MOTION - FORMULA13 - NEWTON’S SECOND LAW OF MOTION - THE SPRINTER14 - NEWTON’s THIRD LAW OF MOTION15 - NEWTON’s THIRD LAW OF MOTION - APPLICATIONS16 - DISTANCE - DISPLACEMENT17 - POSITION18 - SPEED - VELOCITY - DISTANCE-TIME graph19 - ACCELERATION - DECELERATION / VELOCITY-TIME GRAPH20 - VECTORS - A VECTOR / SCALAR21 - VECTORS - ADDING VECTORS22 - MASS - INERTIA - WEIGHT and MASS are DIFFERENT 23 - The 100m SPRINT - VELOCITY - TIME GRAPH / THE START24 - The 100m SPRINT - MIDDLE OF RUN / END OF RUN25 - MOMENTUM26 - FORCE27 - FORCE - PROPERTIES OF FORCE / NET FORCE28 - FORCE - EXAMPLES - NET FORCES29 - FORCE EXAMPLE - NET FORCES - THE HIGH JUMPER AT TAKE

OFF30 - TYPES OF FORCE ACTING ON A SPORT PERFORMER31 - WEIGHT32 - WEIGHT AND MASS

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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

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

Mechanics of Motion

MECH AN I CS ofMOTI ONlinear angular

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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

• force changes the shape of an object

Newton’s Laws of Motion

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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

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

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PIN MEN - FREE BODY DIAGRAMS

SHAPE OF BODY• should be represented

approximately

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

DIAGRAM• shows force in black acting

downwards on the ground


• force in red acting upwards on the jumper’s foot

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DIAGRAM• shows four forces acting• 2 forces acting up on the foot and

down on the body

• 2 forces acting backwards on the body and forwards on the foot

• longer arrows mean greater 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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NEWTON’S LAWS OF MOTION


NEW TON 'S LAW S

1st LAWzero net force

acts- constantvelocity

2nd LAWa net force acts

F= m a- produces

acceleration

3rd LAWone body exertsforce on another

- reaction

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NEWTON’s FIRST LAW

Newton’s Laws of motion

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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NEWTON’s FIRST LAW

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


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

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NEWTON’S SECOND LAW OF MOTION

FORMULA• force = mass x acceleration• F = m x a

• hence the bigger the force the bigger the acceleration

• the bigger the mass, the smaller the acceleration


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

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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 no upward acceleration

• the sprinter runs horizontally

• therefore there is a net backwards force

• producing a negative acceleration• or deceleration

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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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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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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

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

Linear Motion - Measurements

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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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SPEED - VELOCITY

SPEED• = distance moved v = s unit

ms-1 time taken t

• = scalar (no direction)

VELOCITY • = speed in a given direction• = vector

DISTANCE / TIME graph• gradient of graph is velocity


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ACCELERATION

ACCELERATION • = change of velocity a = v - u unit ms-2

time taken to change t

• 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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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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VECTORS

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

• F2 = F12 + F2

2

= tan-1(F2/F1)

• is found by completing the rectangle

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MASS - INERTIA

MASS • the mass of a body or object is the

same everywhere 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, and also hard to stop it once it is moving

• measured in kilogrammes kg

WEIGHT and MASS are DIFFERENT

• 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


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The 100m SPRINT

VELOCITY - TIME GRAPH• steep slope for first part = large

acceleration• this corresponds with a large

forward net force applied at the start


THE START

• net force forwards (resultant) shown in black

• friction is large• provides forward acceleration

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The 100m SPRINT

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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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)

Linear Motion - Momentum

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FORCEFORCE• 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

Force

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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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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FORCEEXAMPLES - NET FORCES• sprinter accelerating• jumper taking off• projectile in flight• jumper landing

– as feet make contact with ground– net force backwards causes

deceleration

Force

EXAMPLES - ZERO NET FORCE• sprinter at full speed• swimmer at full speed

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FORCE

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 :

Force

• 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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TYPES OF FORCE ACTING ON A SPORT PERFORMER

Types of Force

TYPE OF FOR CE

W EI GHT

R EACTI ON

FR I CTI ONAI R R ESI STANCEFLUI D FR I CTI ON

M AGNUS EFFECT

UPTHR UST

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WEIGHTWEIGHT• is produced by the gravitational

force field acting on objects / bodies• it is a force which acts downwards

towards the centre of the Earth

Types of Force - Weight

• 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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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

WEIGHT AND 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

• measured in kilogrammes kg

Types of Force - Weight

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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

• weight lifter pulls up on weight, weight pulls down on lifter

Types of Force - Reaction

• jumper pushes down on the ground, ground pushes up on the jumper

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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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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

• the ground pushes forward on the rear wheel

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REACTIONINTERNAL 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

• 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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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

Types of Force - Friction

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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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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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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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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

Types of Force - Air-resistance / Fluid Friction

FLUI D FR I CTI ON

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)

shape size

speed stream lining

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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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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

• body shape / cross section and clothing (surface material to assist laminar flow)

• are adjusted to minimise fluid friction


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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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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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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

Types of Force

ocr examinations a level physical education a 7875 module 2565 : option b1 part 1

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