1. The following force–time graphs were obtained during the various stages of a runner’s 100-metre sprint.
Using Figure 6, identify which graph is associated with each of the following phases of a 100-metre sprint, giving reasons for your answers:
(i) early in the sprint;
(ii) during the middle part of the sprint; and
(iii) towards the end of the sprint.
(6 marks)

3. A 200 metre runner must exert a large force in a short period of time to generate an impulse. Sketch and label a graph to show the impulse generated during the acceleration phase of a 200 metre race. (3 marks)
A. X Axis – (time)/milliseconds/seconds
B. Y Axis – (force)/Newton’s
C. Shape of graph – negative and positive components of force shown with negative first
D. Positive impulse clearly larger than negative impulse
E. Positive and negative (force) labelled

4. Biomechanics • Mechanics of movement:
– vectors and scalars – velocity, acceleration and
momentum/impulse in sprinting
– Newton’s Laws applied to movements –
application of forces in sporting activities
– projectile motion – factors affecting distance,
vector components of parabolic flight
– angular motion – conservation of angular
momentum during flight, moment of inertia
and its relationship with angular velocity.

5. Newton’s Laws Newton’s three laws Forces acting on athletes
How they can be applied to sporting situations

6. Newton’s 1st Law:
‘Every body at rest, or moving with constant velocity in a straight line, will continue in that state unless compelled to change by an external force exerted upon it.’
The motion of an object will not change without some force acting on it
A stationary object will remain stationary unless something causes it to move
A moving object will continue at a constant speed unless something speeds it up or slows it down.

7. Remember Inertia!
Inertia is the reluctance of a body to move or change its state of motion
Objects will stay in their state of inertia (i.e. stationary or moving at a constant velocity) unless a force overcomes that inertia.

8. Applying Newton's 1st Law:
The athlete will remain stationary in the blocks unless they exert a force to cause them to move (Newton’s 1st Law)
The force must be large enough to overcome their inertia.
Apply Newton’s First Law to three other sporting examples

9. Newton’s 2nd Law:
‘The acceleration of a body is proportional to the force causing it, and the acceleration takes place in the direction in which that force acts.’
This is sometimes expressed by the equation F=ma where:
F = Force
m = Mass
a = Acceleration
This assumes that in most situations, the mass remains constant.

10. Applying Newton's 2nd Law:
The athlete will accelerate away from the blocks in proportion to the force their muscles are applying, and in the direction that their muscles are applying the force (Newton’s 2nd Law)
When the muscles have reached their maximum force generation the athlete will stop accelerating and should continue at a constant velocity (Newton’s 1st Law)
Apply Newton’s Second Law to three other sporting examples

11. Newton’s 3rd Law:
‘When one object exerts a force on a second object, there is a force equal in magnitude but opposite in direction exerted by the second object on the first.’
Or in other words:
For every action, there is an equal and opposite reaction.

13. Applying Newton's 3rd Law:
As the athlete pushes down onto the ground, there is an equal and opposite force pushing the athlete from the ground
This is called the ground reaction force
Apply Newton’s Third Law to three other sporting examples

14. Newton’s 3rd Law

15. Newton’s 3 Laws of Motion

16. Force – Recap from Lesson 1
Force is the ‘push or pull’ exerted on an object or body, which may either cause motion of a stationary body or a speeding up, slowing down or change of direction of a moving body.
Force can be generated internally by or externally by
Without such forces, movement would not be possible, and when such forces are understood and adapted to the same aim, optimal performance can be achieved.
Force is a Vector quantity – what does this mean?
It has magnitude and direction.
Muscle contraction
Gravity, friction, water and air resistance

17. Forces A force is a push or a pull that can change the…
…velocity (therefore causing acceleration or deceleration),
direction…
or shape…
…of an object.

18. There are always many different forces acting on an athlete.
These include Vertical Forces:
Weight
Ground Reaction Force / Buoyancy in water
and Horizontal Forces:
Action Force (or driving force)
Reaction Force (from any object that has been struck)
Drag – which can include:
Friction
Air resistance
Water resistance

19. Sketch the diagram and label the forces being shown by the arrows:

20. Recapping Resultant Forces
The motion of an object depends on the sum of all the forces acting upon it at any one time (i.e. the resultant forces). a) b) c) d) e) f)

21. Net Forces
The motion of an object depends on the sum of all the forces acting upon it at any one time (i.e. the resultant or net forces).
If two forces opposing each other are equal (and opposite) we can say that they are balanced.
This means the net force is zero.
The object will not change its motion.
If the two forces are not opposing each other are unbalanced, then there will be a net force that will change the velocity, direction or shape of the object.
The ball will increase in velocity (accelerate) upwards

22. Drag
Any object in motion, unless in a vacuum, will experience drag (friction, air resistance and / or water resistance).
This always acts in the opposite direction to motion, and slows down the object.
If the action / driving force on an object and the combined forces of friction, air resistance and/or water resistance are equal, the net force would be zero.
The object’s motion would not change – it would remain stationary or moving at a constant speed.
If the action force is larger than drag, the object will accelerate.
If the action force is smaller than drag, the object will decelerate.

23. Friction Caused by two objects rubbing against each other.
Factors affecting friction include:
Roughness of the surfaces
Surface area
Size of the down force / weight
Warmth of the surfaces

24. Air Resistance
Air resistance is the force of air pushing against a moving object. It is a form of fluid friction due to contact between the object and the air.
Factors affecting air resistance are:
Velocity of the object
Frontal cross sectional area
Shape and surface characteristics
Water resistance is the same as air resistance, except it is due to water molecules pushing against a moving object.

25. Free Body Diagrams
Choose a sporting event where a number of forces are in action and label a sketch diagram of that event showing the forces and their magnitude acting upon that body.

26. Apply it…
Ice hockey is often regarded as a very physical game, with many collisions occurring during normal play. A stationary ice-hockey puck was struck with an ice-hockey stick and travelled across the ice until it struck and rebounded from a wall.
The diagram shows the changes in horizontal linear velocity experienced by the puck. Assume that air resistance and friction on the ice are negligible.
Describe and explain the horizontal motion of the puck associated with each of the periods of time identified as P, Q, R, S and T.
(7 marks)

27. P 1. Puck stationary/at rest on the ice/zero horizontal linear velocity;
2. No/negligible net external forces acting; Sub max 1 mark
Q 3. Time when stick in contact with puck/force applied by stick;
4. Puck changing velocity/accelerating/positive linear velocity;
5. In direction of force applied by stick Sub max 2 marks
R 6. Puck travelling with constant (horizontal) velocity;
7. No/negligible net external forces acting/friction free; Sub max 1 mark
S 8. Time when puck hits wall;
9. Puck decelerates . (caused by force applied by wall);
10. Eventually travels in opposite direction/negative horizontal linear velocity/ rebounds off the wall/travels towards the performer. Sub max 2 marks
T 11. Puck moving across ice with constant negative horizontal linear velocity;
12. No/negligible net external forces acting;
13. Reduced velocity (due to energy absorbed by impact). Sub max 1 mark
(Do not credit speed)
7 marks

28. Apply It…
In the Kirrin cycling event, a cyclist has to travel at many different speeds, from slow to sprinting.
Explain, in terms of forces, how a cyclist is able to change and maintain their speed during the course of the race.
(6 marks)

29. Weight and ground reaction force are equal
Action / driving force is cyclists legs on pedals
Opposing force is friction and air resistance (AR).
Friction does not change much during the race.
To accelerate action force must be greater than AR.
As the cyclist speeds up, (AR) increases
When the action force and AR are equal, speed is constant
To increase to a higher velocity, a greater action force must be applied and maintained.
To decelerate, the action force is reduced (by pedalling less hard) so it is less than AR

30. The final stage of an endurance race often involves a sprint finish.
Using Newton’s Second Law of Motion, explain how an athlete is able to accelerate towards the finish line.
(3 marks)
2. Using ‘Newton’s First and Second Laws of Motion’, explain how the swimmer dives off the starting blocks.
(4 marks)