BIOMECHANICAL PRINCIPLES

1. BIOMECHANICAL PRINCIPLES

2. PROJECTILES • the motion of objects in flight • human bodies • shot / discus / javelin / hammer • soccer / rugby / cricket tennis / golf balls • is governed by the forces acting • weight • air resistance • Magnus effect • aerodynamic lift • and the direction of motion

4. FORCE FORCE is push or pull the unit is the NEWTON (10 N is approx the weight of 1 kg) force changes the state of motionof an object force causes acceleration or deceleration or change of direction the more force the bigger the acceleration force changes the shapeof an object WEIGHT FRICTION REACTION FORCES AIR RESISTANCE / FLUID FRICTION all these forces affect the sportsperson Motion and Movement - Newton’s Laws FORCE

5. 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 with zero net force an object is STATIONARY or moves at CONSTANT SPEED in the SAME DIRECTION a sprinter in full stride has four forces acting but they cancel out exactly therefore he / she travels at constant speed Motion and Movement - Newton’s Laws NEWTON’S FIRST LAW of MOTION

6. NEWTON’S SECOND LAW this law is used when a NET FORCE acts on an object net forceFORWARDS produces ACCELERATION net forceBACKWARDS produces DECELERATION net forceSIDEWAYS produces CHANGE OF DIRECTION the bigger theforcethebiggerthe acceleration the sprinter slows downat the end of a race there is a net force backwards so the sprinter decelerates Motion and Movement - Newton’s Laws NEWTON’S SECOND LAW of MOTION

7. 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 actionof jumper down on ground = reactionof ground up on jumper the harder you push down on the ground, the more the ground pushes up on you this upward force on the jumper is the force acting to cause the take off Motion and Movement - Newton’s Laws NEWTON’S THIRD LAW of MOTION

8. EFFECTS of FORCE force causes linearacceleration or deceleration including change of direction the point of actionof a force affects what happens friction acts at the feet of a sportsperson, not enough of it and the person’s feet slip if a force actsthrough the person’s centre of mass (CofM), then linear motion is caused if a force acts to one sideof theCoMthen rotation is caused like take-off in the high jump, the reaction force acts to one side of the CoM Motion and Movement - The Effects of Force The EFFECTS of FORCE

9. CENTRE OF MASS CENTRE of MASS (CoM) • this is the single point in a body which represents all the spread out mass of a body • the weight acts at the CoM since gravity acts on mass to produce weight

10. 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

11. BALANCE and TOPPLING BALANCE • to keep on balance the CoM must be over the base of support

12. 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

13. CENTRE OF MASS - GENERATION OF ROTATION FORCE ACTING AT TAKE-OFF THROUGH CoM • the line of action of a force on a jumper before take-off determines whether or not he rotates in the air after take off • if a force acts directly through the centre of mass of an object, then linear acceleration will occur (Newton's second law), no turning or rotating • example : • basketballer : force acts through CoM therefore jumper does not rotate in air

14. CENTRE OF MASS - GENERATION OF ROTATION FORCE ACTING AT TAKE-OFF NOT THROUGH CoM • a force which acts eccentrically to the centre of mass of a body will cause the body to begin to rotate (will initiate angular acceleration) • this is because the force will have a moment about the CoM and will cause turning • example : • high jumper : force acts to one side of CoM therefore jumper turns in air

15. STABILITY AND BASE OF SUPPORT

16. Stability is defined as the ability to hold or maintain a position in space. 3 key terms Centre of Gravity (COG) the theoretical point where all the body weight is concentrated or the theoretical point about which the body weight is evenly distributed. Line of Gravity (LOG)– a straight line from the COG to the floor Base of Support (BOS) – The area in contact with the floor.

17. There are four basic principles underlying stability. Principle #1 • “The closer the line of gravity is to the centre of the base of support the greater the probability of maintaining balance.”

18. Why is this body in a stable position? • “The line of gravity from the centre of gravity passes through the centre of the base of support.”

19. What happens if we move the line of gravity closer to edges of the base of support? • We become more unstable. The chance of losing balance increases.

20. Principle #2 “The wider the base of support, the greater the probability of maintaining balance” Consider wrestling. Is a wrestler more stable on all fours or standing up? Why? • This is because the size of the base of support is larger so the center of gravity has further to travel to get outside the edges of the base of support so this becomes a stable position.

21. Principle #3 • “The probability of maintaining balance is increased when the centre of gravity is lowered in relation to the base of support. This is because; ;. As the centre of gravity is lowered, the distance the line of gravity has to travel to reach the edges of the base of support is greater than when the center of gravity is higher. What other applications does this principle have in sports? • In some sports we need to lower ourselves to improve stability e,g. a rugby scrum packs in low to improve stability • What are the applications of this principle in sport. • Where balance is important e.g sports such as tennis, gymnastics, hockey, and netball.The body often has to make adjustments to maintain balance.

22. Principle #4 “ The further one body part moves away from the line of gravity, the probability of maintaining balance decreases unless another body part moves to compensate for it.” Consider the person doing the shot put. What have they done to maintain balance in the throw? As the shot putt and trunk moves back the right leg has moved out in the opposite direction to compensate for this to keep balance. This is because; The line of gravity from the centre of gravity is kept above the base of support (foot on ground is base of support).

23. QUESTIONS • Explain the relationship between the 3 components – BOS, COG and LOG • What is the effect of moving the COG outside the body? • What will happen if the LOG falls outside the BOS?

24. LEVERS • levers have an pivot (fulcrum), effort and load • and are a means of applying forces at a distance from the source of the force

25. CLASSIFICATION OF LEVERS • class 1 lever : pivot between effort and load • see-saw lever found rarely in the body • example : triceps / elbow • class 2 lever : load between pivot and effort • wheelbarrow lever, load bigger than effort • example : calf muscle / ankle • class 3 lever : effort between pivot and load • mechanical disadvantage, effort bigger than load, most common system found in body • example : quads / knee and biceps / elbow

26. MOMENT OF INERTIA (MI) • the equivalent of mass for rotating systems • rotational inertia • MI depends on the spread of mass away from the axis of spin, hence body shape • the more spread out the mass, the bigger the MI • bodies with arms held out wide have large MI • the further the mass is away from the axis of rotationincreases the MI dramatically • sportspeople use this to control all spinning or turning movements • pikes and tucks are good examples of use of MI, both reduce MI

27. CONSERVATION OF ANGULAR MOMENTUM ANGULAR MOMENTUM (H) • angular momentum = moment of inertia x angular velocity • = rotational inertia x rate of spin • H = I x w CONSERVATION of ANGULAR MOMENTUM • this is a law of the universe which says that angular momentum of a spinning body remains the same (provided no external forces act) • a body which is spinning / twisting / tumbling will keep its value of H once the movement has started • therefore if MI (I) changes by changing body shape • then w must also change to keep angular momentum (H) the same • if MI (I) increases (body spread out more) then w must decrease (rate of spin gets less) • strictly, this is only exactly true if the body has no contact with its surroundings, as for example a high diver doing piked or tucked somersaults in the air • but it is almost true for the spinning skater !

28. CONSERVATION OF ANGULAR MOMENTUM - EXAMPLES THE SPINNING SKATER • arms wide - MI large - spin slowly • arms narrow - MI small - spin quickly • THE TUMBLING GYMNAST • body position open - MI large - spin slowly • body position tucked - MI small - spin quickly

29. Force Summation STUDENTS WILL HAVE AN UNDERSTANDING OF THE 5 PRINCIPALS OF FORCE SUMMATION

30. FORCE SUMMATION • When we are trying to generate as much momentum as possible in activities such as throwing, kicking and striking the amount of momentum we can give to an object is determined by the sum of all forces generated by the different body parts. This is called force summation.

31. There are 5 basic guidelines for giving an object as much momentum as possible. #1 Using Body Segments • We should look to use as many body segments as possible when trying to give an object maximum momentum. Why? • Because we can maximise the muscular force that each muscle group associated with each segment can generate

32. #2 Stretch out • Before we begin the sequence of movements, such as the hitting, throwing or kicking action we should stretch our muscles out to their optimal length. Why? • It allows the muscle to be contracted with optimal force. It gets the blood flowing through the muscle and helps warm the muscle and therefore decreases the risk of injury.

33. #3 Sequencing of body segments • Generally to give maximum momentum to an object in kicking, throwing and hitting we move larger muscle groups first and the smaller muscle groups closer to the object last. • In effect we use the body like a giant whip. • What are the benefits of this? • The momentum generated by larger segments can be passed on to smaller ones until we make contact/release etc. • In a shot putt illustration, how do we see this principle being applied? • Look at the order of execution sequence • i.e. legstrunkshoulderarmswristhandsfingersshot

34. #4 Timing of Body Segments • Generally to give maximum momentum to an object in kicking, throwing and hitting we need to make sure that the right body segment is adding to the overall momentum at the right time. • What could happen if the timing of the body segments is “out of order”? • Not only does it lack coordination but maximum force generation is lost or lessened • How does correct timing ensure maximum momentum? • It means we use those larger muscle groups first and the smaller muscle groups last.

35. #5 Full range of motion • Generally, to give maximum momentum to an object in throwing, kicking or striking, we need to move the segments through the greatest range of motion as we possibly can. • What are the benefits of this? • The greater the range of motion the higher the speed of the extremities on release/contact.

36. How does correct timing ensure maximum momentum? • No speed or force is lost throughout the entire movement. • We can apply all this information to an example of the javelin throw. • Using your knowledge of generating momentum, explain how the athlete generates maximum momentum to the javelin upon release.

37. ANSWER • They use the large muscle groups of the legs and trunk to initiate the force. This force passes onto the shoulder, arms and finally hand at release. Forces are getting increasingly larger up to release. • The arm is fully extended at the shoulder prior to the throwing action • Timing is legstrunkshoulderarmshand • The arm moves through its full range of movement to maximise lever length and force summation