A 2 Revision Mechanics of movement 1 Biomechanics

A 2 Revision Mechanics of movement 1

Biomechanics Terms: • Displacement; • Velocity; • Acceleration 2

Displacement or Distance Length of journey in meters = distance B A Straight line from start to finish in meters = displacement 3

Displacement and velocity • Velocity displacement divided by time • Displacement and velocity have direction 4

Velocity/time graphs – 100 -m Velocity changes Velocity Time 5

Change in velocity • Average velocity changes • Change in velocity over a period of time is called acceleration Acceleration = final velocity – initial velocity time taken 6

On a velocity-time graph acceleration is shown by the steepness (gradient) of the line Velocity Time 7

deceleration? Velocity zero acceleration? Highest acceleration? Time 8

Vectors and scalars • Displacement, velocity and acceleration have direction as well as magnitude = vectors • Temperature, time, speed, etc do not have direction = scalars 9

Typical Question Explain, in terms of the player moving towards a ball, the difference between velocity and acceleration. (3 marks)

Answer 1. Velocity = rate of change of displacement/displacement ÷ time; 2. How fast/quickly player moves towards ball; 3. Acceleration (not speed) = rate of change of velocity/change in velocity ÷ time (taken to change)/[Vf - Vi] ÷ time/a = � v ÷ t; 4. Push off ground to accelerate (not speed)/change velocity; 5. (Both) have direction/are vectors.

Forces cause movement ; A force is a push or a pull “A force is that which alters or tends to alter state or of of rest a body’s uniform motionin a straight line. ” If a body changes hasforce been applied or direction , a velocity 12

Forces affecting motion • • Action/muscular forces Reaction forces Gravity Air resistance/friction 13

Forces acting on a sprinter Air resistance Gravity Friction Action force of muscular contraction Equal and opposite Ground Reaction Force 14

Forces applied - runner • • • Muscularforces applied to ground Reaction force from ground Gravity Frictionbetween ground and foot Air resistance to forward motion 15

Typical question What forces act on a player when they are running during a game? (3 marks)

Answer 1. 2. 3. 4. 5. Gravity; Friction; Air resistance; Action force/muscular forces; Reaction forces/ground reaction force;

Newton’s Laws • 1 st Law – Law of inertia • A body will remain in its state of motion / restuntil affected by a force • A body has a reluctance to change its state of motion 18

Applying Newton’s 1 st Law • Sprinter remains in set position on blocks until a force causes him to change his state of motion • Ball keeps moving until a force causes it to change its state of motion 19

Momentum • In sporting situations, massremains constant; stays the same therefore inertia • All objects in motion have mass and velocity • Product = momentum • Momentum = quantity of motion 20

Newton’s Laws • 2 nd Law – Law of acceleration • The rate of change of momentum is directly proportional to the force causing the change, and the change takes place in the directionin which the force was applied • In sport, mass remains constant and therefore momentum equates to acceleration 21

Applying Newton’s 2 nd Law direction • The magnitude (size) and of force applied by the sprinter to the blocks direction determines the magnitude and of received acceleration – because mass remains constant force • Acceleration is proportional to applied • F∞a 22

Newton’s Laws • 3 rd Law – Law of Reaction • To every force there is an oppositereaction force equal and 23

Applying Newton’s 3 rd Law • The sprinter applies a muscular force to the reaction ground. This results in a force causing movement • The sprinter cannot move the earth/blocks • Reaction force from ground = Ground Reaction Force 24

Typical question Use Newton’s Laws of motion to explain how a sprinter leaves the starting blocks. (6 marks)

1. 2. 3. 4. 5. 6. 7. 8. 9. Answer Newton’s First law – a body remains in a state of motion until acted upon by a force; Sprinter remains stationary until a force causes them to change their state of motion/overcome their inertia; Newton’s Second Law- body accelerates/changes momentum with a magnitude that depends on magnitude of force causing change (nb not F=ma); Also force gives direction; Sprinter applies force to ground; Magnitude of muscular force determines acceleration given to sprinter; Newton’s Third Law – to every force there is an equal and opposite reaction force; Action/applied force are muscular contractions given to earth; Equal and opposite reaction force moves the lighter mass of the sprinter;

Projectile motion • Flightpath = parabola 27

Components • Motion of projectile has twocomponents • Verticalcomponent • Horizontalcomponent 28

Projectile motion Vertical component Horizontal component Vertical motion is affected by gravity – continually decreasing Horizontal motion is affected by friction – usually negligible 29

Variations in vertical and horizontal components This causes the observed parabolic flight and affects the motion components as follows: 30

Projectile motion Factors affecting distance travelled: • Speed of release • Height of release • Angle of release 31

Typical question Elite golfers use their clubs to overcome the forces acting on the golf ball so that it travels long distances. (i)Describe how the impact of the golf club, gravity and air resistance affect the velocity and acceleration of a golf ball. (4 marks) (ii)The flight of a golf ball is said to be parabolic. Explain the term parabolic and the main factors that limit the distance that a golf ball will travel in flight. (4 marks)

(i) 1. 2. 3. 4. 5. Answer Golf club - Applies force Gives acceleration/changes momentum Gravity - Only affects vertical component of flight Reduces/negative effect on velocity/ decelerates Air resistance - Affects both vertical and horizontal components 6. Reduces/negative effect on velocity/ decelerates (ii) 1. Left and right sides match/mirror each other 2. Height of release – higher height above landing more distance 3. Angle of release – closer to 45° the better 4. Speed of release – more force more speed more distance

Factors affecting the fight of a parabola • Velocity of Release- increase in speed of release = increase in displacement of projectile. • Height of Release- increase in release height= increase in displacement of projectile.

Angle of Release 1) Release height= landing height Lofted pass in footy= 45 degrees 2) Release height> landing height Shot put= < 45 degrees 3) Release height< landing height Bunker shot in golf >45 degrees

Impulse • Force x time • Measured during sprinting – force platforms on track • Displayed as Force. time graph 36

• Impulse = force x time • shown as area under graph positive force time negative 37

• Impulse is mainly concerned with single events – a footfall • Involves horizontal forces only • Two parts to a footfall landing – negative horizontal forces Push-off – positive horizontal forces 38

Typically Push-off positive impulse pos time force neg Landing negative impulse Net impulse is difference between positive and negative impulses 39

Typically Large positive impulse pos time force neg Small negative impulse Net impulse is positive – performer is accelerating 40

Typically Small positive impulse pos time force neg Large negative impulse Net impulse is negative – performer is decelerating 41

Typical question (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)

(i) 1. 2. 3. (ii) 1. 2. 3. 4. 5. 6. 7. 8. Answer Impulse is force x time/force applied in unit of time; Equates to change in momentum; If mass constant equates to change in acceleration; 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; 9. Negative and positive components of force labelled;

Angular motion • During free rotation – angular momentum remains constant • This situation occurs when somersaulting and spinning during flight and during ice-skating (ignore friction) 44

Angular Momentum • Angular momentum is the quantity of rotation • Angular momentum = angular velocity x moment of inertia • Angular velocity = rate of rotation or spin • Moment of inertia = spread of body’s mass 45

Constant angular momentum • If you change the moment of inertia; then the angular velocity also changes • Tuck body up small to lower moment of inertia and increaseangular velocity • Seen during somersaults and ice-skating spins 46

Typical question Explain the mechanical principles that allow spinning ice-skaters to adjust their rate of spin. (6 marks)

Answer 1. Ice may be regarded as a friction free surface/friction is negligible; 2. During spins angular momentum remains constant; 3. Angular momentum is the quantity of rotation; 4. Angular momentum = angular velocity x moment of inertia; 5. Angular velocity = rate of spin/how fast skater spins; 6. Moment of inertia = distribution/spread of mass around axis; 7. Changing/reducing moment of inertia affects/increases angular velocity; 8. Skater brings arms into body allowing rate of spin to increase;