1. Year 9/10 Physical Education
Biomechanics
The study of forces and their effects on the human body
Year 9/10 Physical Education

2. Lesson 1
Motion and Resistance

3. Biomechanics in sports, can be stated as the muscular, joint and skeletal actions of the body during the execution of a given task, skill and/or technique. Proper understanding of biomechanics relating to sports skill has the greatest implications on: sport's performance, rehabilitation and injury prevention, along with sport mastery. As noted by Doctor Michael Yessis, one could say that best athlete is the one that executes his or her skill the best.
What is Biomechanics???

4. Characteristics of motion
Linear motion
Motion that occurs in a straight line, it will remain that way unless a certain type of force acts on it (Tennis ball being thrown in the air and then hit by a tennis racket). All parts of the body move in the same direction and at the same speed (e.g. jumping up in the air to catch a ball, a 100m sprint or travelling in a car).
However as you will see in the videos that this motion may change into angular motion after the activity is performed. (e.g once the ball is caught in the lineout or once the runner has finished the race).
Line out jumper in Rugby Union
Characteristics of motion
Drag Racing

5. Characteristics of motion
Angular motion
Motion that occurs around an axis. This axis can be internal (e.g. body parts rotating around a joint) or external (e.g. spinning a ball on your finger).
Spinning a ball on your finger
Spinning figure skater
Characteristics of motion

6. Characteristics of motion
General Motion
A combination of linear and angular motion. This is the most common of all movements, as most human movement requires the rotation of body parts around joints (e.g. cycling, swimming and running). Sometimes it is easier to look at one body to tell what type of motion it is.
Characteristics of motion

7. Characteristics of motion
Apply your knowledge!
Classify the following physical activities as linear motion or angular motion or general motion.
Horse racing
Football dive
Slam Dunk
Boxing punch
Hand Stand
Somersault
Characteristics of motion

8. Resistance What is resistance? What are some examples of resistance?
G………, W……., S………,W……..
What is an example of each of the above resistances in sport?
Resistance

9. Like the ice skater we can increase and decrease our rotational speed by bringing body parts closer to the middle or further away. Due to having less resistance.
Pick two people in the class to spin on a computer chair. Is the theory right? Is it easier to spin when body parts are closer?
Experiment time….

10. Why is Resistance important
Class Discussion
What would sport be like with out resistance?
Sailing, Ten pin bowling, Golf, Goal kicking
Think about the moon?
There is less gravity on the moon compared to earth, what would sport be like there?
Why is Resistance important

11. Centre of Gravity and B.O.S
Lesson 2
Centre of Gravity and B.O.S

12. Centre of gravity can be defined as “the single point at which all parts of an object are equally balanced”.
For a ‘normal’ human being standing upright, their centre of gravity lies around the area of their navel.
A persons centre of gravity can change depending on their body position because as mentioned before, the centre of gravity is the exact point where all parts of an object are equally balanced.
The centre of gravity can also lie outside an object, especially if the object is bent over or leaning in a certain direction
Centre of gravity

13. Centre of gravity Centre of gravity for a “normal person”

14. Centre of gravity for a person whose hands a stretched in the air

15. Centre of gravity Centre of gravity outside of a persons body

16. How do we work out centre of gravity?
The C.O.G is half way between the top and the bottom of the object, both sides are equal.
How do we work out centre of gravity?

17. Experiment time…. Which person has the best balance lets test.
Why is it easier to push someone with a higher C.O.G over?
Experiment time….

18. Line of gravity is the vertical line that passes through the centre of gravity to the ground.
If the line of gravity falls within the object’s base of support (i.e. its contact with the ground), the object is relatively stable.
If the line of gravity falls outside the object’s base of support (i.e. its contact with the ground), the object is relatively unstable.
Line of gravity - The line of gravity is important when determining the stability of an object.

19. Line of gravity Line of gravity Line of gravity Centre of gravity
STABLE
UNSTABLE

20. BOS is the area within an objects point of contact with the ground
BOS is the area within an objects point of contact with the ground. The larger the area the base of support covers, the more stable an object will be.
Narrow BOS
Wide BOS
BOS
BOS
Base of support – The object on the left is more stable because of its relatively larger BOS

21. Test what is more stable a big base of support, a shoulder width or feet together
Why is this the best?
Experiment

22. Line of gravity, BOS in relation to movement
The line of gravity (LOG) must go outside the base of support to initiate or continue movement.
The direction that the line of gravity takes relative to the BOS will be the direction of the resulting movement.
The further away the LOG is from the BOS, the greater the tendency the body has to move in that direction. E.g. Evasive running.
Line of gravity
Top of body moves towards LOG
Direction of movement
Leg pushes against the ground
Line of gravity, BOS in relation to movement
Base of support

23. Apply your knowledge!
Label the following images with the COG, LOG and BOS.
Is the performer stable?
Centre of gravity, Line of gravity, Base of support and Physical activity

24. Name 3 ways to ensure you are stable (use biomechanical terms)
In relation to stability, what is one advantage of being shorter? (use biomechanical terms)
When you do a right handed lay up, what movement is occurring at your right hip?
What is the agonist muscle causing this movement?
What is the antagonist muscle during this movement?
5 Quick Questions

25. Newton's first law of motion
Lesson 3
Newton's first law of motion

26. When exploring the area of biomechanics and human movement, it is useful to look at motion through the observations made by Sir Isaac Newton.
Newton was a famous seventeenth- century scientist who developed the three laws that govern all motion.
Newton’s Laws

27. Newton’s 1st Law – The law of inertia.
‘A body continues in its state of rest or uniform motion unless an unbalanced force acts upon it.’
In other words, a body will remain at rest or in motion unless acted upon by a force. In order to get a body moving, a force must overcome the body’s tendency to remain at rest or inertia. The amount of inertia a body has depends on its mass.
What does inertia mean? A persons mass or body weight. For example to push someone you must over come there weight.
Newton’s 1st Law – The law of inertia.

28. Newton’s 1st Law of Motion

29. The 175kg weights have more inertia because it has a greater mass
Which has more inertia a 100kg person or a 175kg weight? Why?
The 175kg weights have more inertia because it has a greater mass
Having a great deal of inertia can be advantageous in some sporting situations. How?
If you have a lot of inertia you can be difficult to move e.g. in a rugby scrum, wrestling, judo
Of course having a lot of inertia has disadvantages as well in sporting situations. How?
If you have a lot of inertia, you require a lot of force or effort to get you moving. It can also mean a decrease in agility.

30. What is meant by unbalanced force?
If the forces on an object are equal and opposite, they are said to be balanced, and the object experiences no change in motion. If they are not equal and opposite, then the forces are unbalanced and the motion of the object changes.
What is meant by unbalanced force?

31. Newton’s 1st Law – The law of inertia
This soccer ball will remain at rest, until a force acts on it – What is the force that acts upon the ball?
What are some other examples of objects remaining at rest or in motion? Give examples in hockey, golf, rugby kicking
Newton’s 1st Law – The law of inertia

32. Two teams are playing tug of war
Two teams are playing tug of war. They are both exerting equal force on the rope in opposite directions. This balanced force results in no change of motion.

33. Once airborne, unless acted on by an unbalanced force (gravity and air – fluid friction), it would never stop!
1st Law

34. Why was it so difficult to stop the TITANIC from colliding with the iceberg?

35. The mass of the Titanic is very large.
Inertia is proportionate to mass.
The Titanic could not change its direction because its extremely high inertia forces it to continue in a straight line, thereby colliding with the iceberg.
menu

36. Basically, an object will “keep doing what it was doing” unless acted on by an unbalanced force.
If the object was sitting still, it will remain stationary. If it was moving at a constant velocity, it will keep moving.
It takes force to change the motion of an object.
Recap

37. Newton's second law of motion
Lesson 5
Newton's second law of motion

38. Newton’s 2nd Law – Mass, force & acceleration
‘The acceleration of an object is directly related to the force causing it, is in the same direction as the force, and is inversely proportional to the mass of the object’.
Imagine a ball of a certain mass moving at a certain acceleration. This ball has a certain force
When a force is applied to an object it will move in the direction the force was applied, and, depending on the size of the force and the size of the object, the object will accelerate accordingly.
What does F = ma mean?
Newton’s 2nd Law – Mass, force & acceleration

39. Now imagine the original ball moving at twice the original acceleration. F = ma says that the ball will again have twice the force of the ball at the original acceleration.
Now imagine we make the ball twice as big (double the mass) but keep the acceleration constant. F = ma says that this new ball has twice the force of the old ball.
A smaller object will move faster than a larger object.
A greater force will move an object faster than a smaller force.

40. Imagine a ball of a certain mass moving at a certain acceleration
Imagine a ball of a certain mass moving at a certain acceleration. This ball has a certain force. Now imagine we make the ball twice as big (double the mass) but keep the acceleration constant. F = ma says that this new ball has twice the force of the old ball. Now imagine the original ball moving at twice the original acceleration. F = ma says that the ball will again have twice the force of the ball at the original acceleration.

41. What does F = ma say?
F = ma basically means that the force of an object comes from its mass and its acceleration.
Something very massive (high mass) that’s changing speed very slowly (low acceleration), like a glacier, can still have great force.
Something very small (low mass) that’s changing speed very quickly (high acceleration), like a bullet, can still have a great force. Something very small changing speed very slowly will have a very weak force.

42. Newton's third law of motion
Lesson 6
Newton's third law of motion

43. Newton’s 3rd Law – action & reaction
‘Whenever a force is applied there is an equal and opposite reaction.’
If an athlete exerts a force onto the ground in order to push off, the ground will exert an equal and opposite force on the athlete, pushing them up into the air.
The first force of the athlete pushing into the ground is called an action force. The second force is called the reaction force (when the second body applies an opposing force back).
Newton’s 3rd Law – action & reaction

44. Newton’s 3rd Law – action & reaction

45. Flying gracefully through the air, birds depend on
So When you sit in your chair, your body exerts a downward force on the chair and the chair exerts an upward force on your body.
Flying gracefully through the air, birds depend on
Newton’s third law of motion. As the birds push down
on the air with their wings, the air pushes their wings up
and gives them lift.
Reaction
Force

46. The reaction of a rocket is an application of the third law of motion
The reaction of a rocket is an application of the third law of motion. Various fuels are burned in the engine, producing hot gases.
The hot gases push against the inside tube of the rocket and escape out the bottom of the tube. As the gases move downward, the rocket moves in the opposite direction.

47. Lesson 4
Levers

48. What is a force?
A push, pull or twist that causes movement of an object
Force = Mass x Acceleration
Levers are used to apply a force
Force

49. Levers – are used to apply force
Consist of a pivot point (fulcrum) and a lever arm (connecting the pivot point to the resistance).
Downward Pressure
Resistance
Fulcrum (pivot point)
Lever arm
Levers – are used to apply force

50. The amount of leverage a person processes is dependent on the length of their body, in particular the length of their arms and legs.
Longer levers result in greater speed at the end of the lever arms – this is beneficial for throwing and striking objects.
Short levers can be moved with less force and at greater speeds – this is beneficial for moving body parts quickly and applying strength for pushing, pulling and lifting objects.
Question: From this information, what can you assume about a shorter person in comparison to a taller person?
Levers

51. In the human body, levers are made up of the joints (fulcrum) and the bones that connect them to the objects being moved.
Levers in the human body can be manipulated to improve speed and apply large forces at the same time
Example: Running – lifting your foot and knee up will create a shorter lever, therefore you can run faster
Using Levers in Sport

52. Lesson 7
Exam time