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Jan Roscoe Publications AQA Examinations AS and A Level Physical Education AS / A year 1 (A1) AS 7581 Section 3.1 Factors affecting participation in physical activity and sport 3.1.5 Biomechanical movement 3.1.5.1 Biomechanical principles INDEX 3.1.5 Biomechanical movement 3 4 7 8 11 15 21 22 23 24 25 26 29 31 33 34 index AQA AS / A1 Level Physical Education NEWTON’s LAWS OF MOTION NEWTON’s FIRST LAW OF MOTION NEWTON’s FIRST LAW OF MOTION - THE EFFECT OF FORCES NEWTON’s SECOND LAW OF MOTION NEWTON’s THIRD LAW OF MOTION EXAMPLES OF NEWTON’s THIRD LAW REACTION DISTANCE DISTANCE - DISPLACEMENT POSITION SPEED - VELOCITY CENTRE OF MASS (GRAVITY) BALANCE and TOPPLING BALANCE and TOPPLING - STABILITY and TOPPLING BALANCE and TOPPLING - FACTORS AFFECTING STABILITY BALANCE and TOPPLING previous next 3.1.5.1 biomechanical principles 2 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education NEWTON’s LAWS OF MOTION 1st LAW zero net force acts - constant velocity 2nd LAW a net force acts F=ma force produces acceleration NEWTON's LAWS 3rd LAW one body exerts force on another - reaction index previous next 3.1.5.1 biomechanical principles 3 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education NEWTON’s FIRST LAW 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 index previous next 3.1.5.1 biomechanical principles 4 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education NEWTON’s FIRST LAW OF MOTION NEWTON’S FIRST LAW • 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 or she travels at constant speed index previous next 3.1.5.1 biomechanical principles 5 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education NEWTON’s FIRST LAW OF MOTION 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 index previous next 3.1.5.1 biomechanical principles 6 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education NEWTON’s FIRST LAW OF MOTION 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 • • for the sprinter, vertical arrows are the same size and therefore cancel out horizontal forces are the same size and therefore also cancel out index previous next 3.1.5.1 biomechanical principles 7 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education 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 index previous next 3.1.5.1 biomechanical principles 8 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education NEWTON’s SECOND LAW OF MOTION NEWTON’S SECOND LAW FORMULA • force = mass x acceleration F = m x a index • hence the bigger the force the bigger the acceleration • the bigger the mass, the smaller the acceleration previous next 3.1.5.1 biomechanical principles 9 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education NEWTON’s SECOND LAW OF MOTION THE SPRINTER index previous next • four forces are acting • upwards force = downwards force • therefore there is no upward acceleration • the sprinter runs horizontally • net horizontal forces act backwards • there is a net backwards force • producing a negative acceleration • or deceleration 3.1.5.1 biomechanical principles 10 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education 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 Helen Roscoe Photography index previous next 3.1.5.1 biomechanical principles 11 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education NEWTON’s THIRD LAW OF MOTION NEWTON’S THIRD LAW • 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 index previous next 3.1.5.1 biomechanical principles 12 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education NEWTON’s THIRD LAW OF MOTION APPLICATIONS • at the swim start - the swimmer pushes back on the blocks as hard as possible • the blocks push forward - and provides forward acceleration - on the swimmer Helen Roscoe Photography index previous next 3.1.5.1 biomechanical principles 13 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education NEWTON’s THIRD LAW OF MOTION APPLICATIONS • a swimmer drives backwards on water with hands and feet (force in black) • index the water pushes the swimmer forward (force in red) previous next 3.1.5.1 biomechanical principles 14 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education EXAMPLES OF NEWTON’s THIRD LAW 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 index previous next 3.1.5.1 biomechanical principles 15 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education EXAMPLES OF NEWTON’s THIRD LAW 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 index previous next 3.1.5.1 biomechanical principles 16 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education EXAMPLES OF NEWTON’s THIRD LAW REACTION FORCES • swimmer pushes backwards on the water • index reaction force thrusts the swimmer forward previous next 3.1.5.1 biomechanical principles 17 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education EXAMPLES OF NEWTON’s THIRD LAW REACTION FORCES • canoeist pushes backwards on the water • index reaction force thrusts the canoe forward previous next 3.1.5.1 biomechanical principles 18 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education EXAMPLES OF NEWTON’s THIRD LAW REACTION FORCES • sprinter pushes back and down on the ground • index the ground pushes upwards and forwards on the sprinter previous next 3.1.5.1 biomechanical principles 19 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education EXAMPLES OF NEWTON’s THIRD LAW REACTION FORCES • in cycling, the tyre on the rear wheel pushes backward on the ground • the ground pushes forward on the rear wheel index previous next 3.1.5.1 biomechanical principles 20 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education 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 • • • 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 index previous next 3.1.5.1 biomechanical principles 21 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education DISTANCE 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 • index unit the metre m previous next 3.1.5.1 biomechanical principles 22 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education DISTANCE - DISPLACEMENT 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! • index previous unit the metre m next 3.1.5.1 biomechanical principles 23 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education POSITION POSITION • a way of explaining where a point is relative to some fixed point index • 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. previous next 3.1.5.1 biomechanical principles 24 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education SPEED - VELOCITY SPEED • = distance moved v = s unit ms-1 time taken t • = scalar (no direction) • = distance moved in 1 second VELOCITY • = speed in a given direction • = vector DISTANCE / TIME graph • gradient of graph is velocity index previous next 3.1.5.1 biomechanical principles 25 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education CENTRE OF MASS (GRAVITY) CENTRE of MASS (CoM) • this is the scientific term for centre of gravity since the concept is not dependent on gravity • CoM is the single point in a body which represents all the spread out mass of a body • index the weight acts at the CoM since gravity acts on mass to produce weight previous next 3.1.5.1 biomechanical principles 26 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education CENTRE OF MASS (GRAVITY) WHERE IS THE CENTRE OF MASS? • position of centre of mass depends on shape of body • this is how the high jumper can have his CoM pass under the bar • but he could still clear the bar index previous next 3.1.5.1 biomechanical principles 27 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education CENTRE OF MASS (GRAVITY) WHERE IS THE CENTRE OF MASS? • note the position of this person’s centre of mass (red dot) Helen Roscoe Photography index previous next 3.1.5.1 biomechanical principles 28 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education BALANCE and TOPPLING BALANCE • to keep on balance the CoM must be over the base of support index previous next 3.1.5.1 biomechanical principles 29 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education BALANCE and TOPPLING TOPPLING • the CoM must be over the base of support if a person is to be on balance • toppling would be caused by the weight acting at the CoM creating a moment about the near edge of the base of support • this can be used by divers or gymnasts to initiate a controlled spinning (twisting) fall and lead into somersaults or twists index previous next 3.1.5.1 biomechanical principles 30 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education BALANCE and TOPPLING STABILITY and TOPPLING • the CoM must be over the base of support if a person is to be on balance • so a person holding a balance is said to be in equilibrium • like a person holding a handstand • this is an unstable equilibrium because a very small force could cause the CoM to move enough to topple the person Helen Roscoe Photography index previous next 3.1.5.1 biomechanical principles 31 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education BALANCE and TOPPLING STABILITY and TOPPLING • the CoM must be over the base of support if a person is to be on balance • • so a ball sitting on the floor can be said to be in equilibrium – in this case neutral equilibrium – since a small sideways force will cause the ball to move, but remain in equilibrium – still stable to toppling as is a gymnast lying on the floor! index previous next 3.1.5.1 biomechanical principles 32 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education BALANCE and TOPPLING FACTORS AFFECTING STABILITY • the CoM must be over the base of support if a person is to be stable • hence the bigger the area of the base of support, the further the CoM would have to be moved to make the situation unstable (would topple) • so for a rugby player receiving a tackle, he would be more stable if his / her feet were as wide apart as possible • also, the higher the CoM, the less stable a person would be, so the rugby player would crouch low to lower his / her CoM to make his / her situation more stable index previous next 3.1.5.1 biomechanical principles 33 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education BALANCE and TOPPLING STABILITY and TOPPLING • the CoM must be over the base of support if a person is to be on balance • so a beam gymnast will need careful control of the position of her CoM if she is not to fall off index previous next 3.1.5.1 biomechanical principles 34 3.1.5 Biomechanical movement AQA AS / A1 Level Physical Education BALANCE and TOPPLING TOPPLING • during a swim start, the swimmer topples forward • by adjusting the line of action of the weight acting through the CoM so that it falls in front of his / her feet • and then allows the toppling to tip him / her forwards into the water • • when the body is almost horizontal, he / she drives hard with the legs on the start platform to propel him / her forward into the race index previous next 3.1.5.1 biomechanical principles 35