1. Quick Questions Describe Newton’s 1st Law of Motion (1)
Describe Newton’s 2nd Law of Motion (1)
Describe Newton’s 3rd Law of Motion (1)
Give an example of each of the Laws in action (3)

2. Biomechanical Principles – Forces & Free Body Diagrams
Biomechanics
Biomechanical Principles – Forces & Free Body Diagrams

3. Most: Apply your knowledge of forces in a variety of sporting examples
Learning Objectives
Learning Objective:
Understand how the different forces acting on a body affect performance
- net force, balanced force, unbalanced force, vertical forces, horizontal forces, weight, reaction, friction, air resistance, momentum, acceleration
Learning Outcomes:
All: Describe the different forces, calculate them and label them correctly on a free body diagram
Most: Apply your knowledge of forces in a variety of sporting examples
Some: Explain how athletes can use their knowledge of forces to maximise performance

4. Key Terms Use a book to define each of the following terms: Net force
Balanced force
Unbalanced force
Vertical forces
Horizontal forces
Weight
Reaction
Friction
Air resistance
Momentum
Acceleration

5. Key Terms
Net force – the overall force acting on a body when all the individual forces have been considered.
Balanced force - when two or more forces acting on a body are equal in size but opposite in direction. The resultant net force is zero
Unbalanced force - when force acting in one direction is greater in size than a force acting in the opposite direction. The resultant net force is either positive or negative.
Vertical forces - weight and reaction
Horizontal forces - friction and air resistance
Weight - the force on a body exerted by the Earth’s attraction (N) the arrow goes from the centre of mass (usually belly button) down to the floor
Reaction - for every action there is an equal and opposite reaction. the arrow goes from each point in contact with the floor upwards If weight > reaction, movement is downwards If reaction> weight, movement is upwards
Friction - the force that acts in opposition to the movement of one surface over another the arrow goes forwards from the points in contact with the floor
Air resistance - the force acting in the opposite direction to the motion of a body travelling through air the arrow goes backwards from the centre of mass If Friction > air resistance you are accelerating If air resistance > friction, you are decelerating
Momentum - the quantity of motion possessed by a moving body. (mass x velocity (kgms-1)
Acceleration - the rate of change of velocity ((vf-vi)/t) (m/s/s)

6. What type of force is this?
Rugby scrum

7. Vertical Forces on a Free Body DiagramW
Reaction – comes from the points in contact with the floor upwards
Weight – an arrow going down to the floor from the belly button

8. Horizontal Forces on a Free Body DiagramAR F F
Friction – from the points in contact with the floor in the same way as the direction of motion
Air Resistance – from the belly button going opposite to the direction of motion

9. Free Body Diagram of a Sprinter
Direction of motion F AR R W
If the athlete is moving forwards the Friction must be bigger than the Air Resistance
If the athlete isn’t moving up or down the Weight and Reaction forces should be the same length
If the athlete is standing still there won’t be horizontal forces acting on them
If Air Resistance is bigger than Friction it means they will be decelerating, but direction of motion will still be forwards

10. If F > AR – accelerating forwards
If F = AR – standing still
If F< AR – decelerating forwards (slowing down)
If W > R – moving downwards
If W = R – no vertical movement
If W < R – moving upwards
If body is off the floor there is no R

11. What forces act on a sprinter out of the blocks?

12. What forces are acting on this basketball player doing a slam dunk?

13. What forces are acting on this athlete as they take off for a box jump?

14. Factors that affect friction
Friction is affected by
surface characteristics
rough surface = more friction (spikes on athletics track)
smooth surface = less friction (ski’s on ice)
tennis – clay courts are rough, so they have a higher friction = ball is slower after the bounce), finely mowed grass courts at Wimbledon, less friction = faster balls.
temperature of the two surfaces
an increase in temperature will either increase or decrease the friction depending on surface characteristics
ski on snow – increased temp – reduces friction
rubber surfaces e.g. tyres become sticky when warm – increasing friction

15. Exam Questions
June 2014 – A basketball player jumps vertically during a match. Draw a free body diagram to show the vertical forces acting on the basketball player during take-off. Explain the relationship between the size of the vertical forces and their impact on the size of the resulting vertical jump. (5)
June a) Fig 2 shows a hockey player taking a penalty flick at goal. Sketch a free body diagram showing all the forces acting on the hockey ball as it is being flicked. Using Newton’s Laws of Motion, explain the effect of the resultant force acting on the hockey ball. (6)
Jan d) Using free body diagrams, analyse the concepts of balanced and unbalanced forces in both horizontal and vertical directions in sport. (20)