1 A2 Revision Mechanics of movement

2 Biomechanics Terms: Displacement; Velocity; Acceleration

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

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

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

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

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

8 Velocity Time Highest acceleration? zero acceleration? deceleration?

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

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.

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

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

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

15 Forces applied - runner forces applied to ground Reaction force from between ground and foot Air resistance Muscular ground Gravity Friction to forward motion

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

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

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

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

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

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

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

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

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

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

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

27 Projectile motion Flightpath = parabola

28 Components Motion of projectile has components component two Vertical Horizontal

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

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

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

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)

Answer (i) 1.Golf club - Applies force 2.Gives acceleration/changes momentum 3.Gravity - Only affects vertical component of flight 4.Reduces/negative effect on velocity/ decelerates 5.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

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

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

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

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

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

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

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)

Answer (i) 1.Impulse is force x time/force applied in unit of time; 2.Equates to change in momentum; 3.If mass constant equates to change in acceleration; (ii) 1.Positive clearly larger than negative; 2.x axis – time; 3.y axis - force; 4.Units of force shown as Newtons; 5.Units of time shown as milliseconds/less than 1 second 6.Time intersecting at zero on force axes; 7.Positive and negative force axes labelled; 8.Shape of graph - negative and positive components of force shown with negative first; 9.Negative and positive components of force labelled;

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

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

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

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;