Biomechanics Module

Newton’s laws

Musculoskeletal levers and mechanical advantage

Classification of force systems

Vector addition and resolution

Newton’s Laws

Law of Inertia Law of Acceleration Law of Action-Reaction

Biomechanics Module

2

Law of Inertia (equilibrium)

 

3 Hall, Basic Biomechanics, 5th ed

Biomechanics Module

Law of Inertia (equilibrium)

 

Biomechanics Module

4

Law of Acceleration

 

5

Biomechanics Module

Law of Acceleration

 

6

Biomechanics Module

Law of Acceleration

   

7

Biomechanics Module

10 pounds

Law of Acceleration

 

Biomechanics Module

8

B

Newton’s Laws

Law of Inertia Law of Acceleration Law of Action-Reaction

Biomechanics Module

9

Within object

Between objects

Law of Action-Reaction

For every action, there is an equal and opposite reaction

(Forces occur in pairs) Between two objects

10

Biomechanics Module

Law of Action-Reaction

For every action, there is an equal and opposite reaction

(Forces occur in pairs) Between two objects Objects must be in contact

11

Biomechanics Module

Law of Action-Reaction

For every action, there is an equal and opposite reaction

12

Biomechanics Module

Law of Action-Reaction

Ground reaction force

13

Hall, Fig 12-1

Body weightGRF =

Biomechanics Module

Musculoskeletal Levers

Why is Charlie Brown up in the air?

14

Biomechanics Module

Musculoskeletal Levers

Why is Charlie Brown up in the air?

15

Biomechanics Module

Musculoskeletal Levers

(Force A)(MAA) vs (Force B)(MAB)

Charlie Brown is up in the air if: (Charlie’s force)(MA) < (Linus’ force)(MA)

16

Force A

Force Bfulcrum,

pivot point

MAA MAB

Biomechanics Module

Musculoskeletal Levers

Interaction between the forces or loads on the segment and the joint

Levers: two forces and a pivot point (fulcrum, axis) Internal force (muscle) External load (gravity etc) Pivot point (joint)(N.B. not consistent w/ Levangie)

17

Biomechanics Module

Musculoskeletal Levers

First class lever Second class lever Third class lever

Differentiated by the relative position of the internal force, external load, and pivot point

18

Biomechanics Module

Musculoskeletal Levers

First class lever

19

Internal force

fulcrum, pivot point

External load

Biomechanics Module

Musculoskeletal Levers

Second class lever

20

Internal force

fulcrum, pivot point

External load

Biomechanics Module

Musculoskeletal Levers

Third class lever

21

Internal force

fulcrum, pivot point

External load

Biomechanics Module

Mechanical advantage

 

22

Biomechanics Module

Mechanical advantage

 

23

Ext Int

fulcrum, pivot point

External MA Internal MA=

First Class Lever

Mech Adv = 1 if fulcrum in middle

Ext

Biomechanics Module

Mechanical advantage

 

24

External MA Internal MA<

Int

fulcrum

Second Class Lever

Mech Adv > 1

Ext

Biomechanics Module

Mechanical advantage

 

25

External MA Internal MA>

Int

fulcrum

Third Class Lever

Mech Adv < 1

Ext

Biomechanics Module

Classification of force systems

Linear same segment same plane same line

26

Biomechanics Module

Classification of force systems

Linear same segment same plane same line

Concurrent same segment same plane common point of application

27

Biomechanics Module

Classification of force systems

Linear same segment same plane same line

Concurrent same segment same plane common point of application

Parallel same segment same plane parallel to each other

28

Biomechanics Module

Fun with Forces

Vector addition Composition Tip to tail Parallelogram

Vector resolution Graphical Trigonometric

Application to human movement Parallel forces Perpendicular forces

Biomechanics Module

29

Vector addition

Composition Works with collinear vectors

Same direction (addition)

Opposite direction (“subtraction”)

30

Hall, Fig 3-11, 3-12

Biomechanics

+ =

+ =

Vector addition

Addition (composition)

31

Hall, Fig 3-11, 3-12

Works with collinear vectors

Biomechanics

Vector addition

Addition (composition)

32

Hall, Fig 3-11, 3-12

Works with collinear vectors

Biomechanics

Vector Addition Tip to tail

Concurrent vectors (vectors which can intersect)

33

Hall, Fig 3-13

Biomechanics

+ =

+ =

=

=

Vector addition Addition – tip to tail

34

Hall, Fig 3-13

Biomechanics

Vector addition Addition – tip to tail

35

Hall, Fig 3-13

Biomechanics

Vector Addition

Addition – parallelogram

36

Hall, Fig 3-13

Biomechanics

+ =

+ =

=

=

Vector addition Addition – parallelogram

37

Hall, Fig 3-13

Biomechanics

Vector addition Addition – parallelogram

38

Hall, Fig 3-13

Biomechanics

Vector Resolution

Resolving a vector into perpendicular components Methods:

Graph paper Trigonometry

39

Biomechanics

Vector Resolution

Graphically

40 Hall, Fig 3-15

Biomechanics

Vector Resolution

Graphically

41 Hall, Fig 3-15

Biomechanics

Vector Resolution

Graphically

42 Hall, Fig 3-15

Biomechanics

Vector Resolution

Trigonometric

43

Hall, Fig 3-15

 

Angle Sin Cos

0 0 1

30 0.50 0.87

45 0.71 0.71

55 0.82 0.57

60 0.87 0.5

90 1 0

Biomechanics

60°

30°

opposite

oppositeadjacent

adjacenthypo

tenu

se

hypo

tenu

se

Vector Resolution

Trigonometric

44

Hall, Fig 3-15

 

Angle Sin Cos

0 0 1

30 0.50 0.87

45 0.71 0.71

55 0.82 0.57

60 0.87 0.5

90 1 0

Biomechanics

60°

30°

opposite

oppositeadjacent

adjacenthypo

tenu

se

hypo

tenu

se

 

Vector Resolution

Trigonometric

45

Hall, Fig 3-15

 

Angle Sin Cos

0 0 1

30 0.50 0.87

45 0.71 0.71

55 0.82 0.57

60 0.87 0.5

90 1 0

Biomechanics

60°

30°

opposite

oppositeadjacent

adjacenthypo

tenu

se

hypo

tenu

se

 

8.7

5.0

10

Vector Resolution

Trigonometric

46

Hall, Fig 3-15

 

Angle Sin Cos

0 0 1

30 0.50 0.87

45 0.71 0.71

55 0.82 0.57

60 0.87 0.5

90 1 0

Biomechanics

60°

30°

opposite

oppositeadjacent

adjacenthypo

tenu

se

hypo

tenu

se

 

10

Vector Resolution

Trigonometric

47

Hall, Fig 3-15

 

Angle Sin Cos

0 0 1

30 0.50 0.87

45 0.71 0.71

55 0.82 0.57

60 0.87 0.5

90 1 0

Biomechanics

60°

30°

opposite

oppositeadjacent

adjacenthypo

tenu

se

hypo

tenu

se

 

8.7

5.0

8.7

5.0

10 10

Vector Resolution

Trigonometric

48

Hall, Fig 3-15

 

55°

Angle Sin Cos

0 0 1

30 0.50 0.87

45 0.71 0.71

55 0.82 0.57

60 0.87 0.5

90 1 0

Biomechanics

20

20cos(55) = 11.4

20si

n(55

) =

16.

4

Vector Resolution

Trigonometric

49

Hall, Fig 3-15

 

55°

45°

30°

Angle Sin Cos

0 0 1

30 0.50 0.87

45 0.71 0.71

55 0.82 0.57

60 0.87 0.5

90 1 0

Biomechanics

Hypotenuse = 100

Vector Resolution

Trigonometric

50

Hall, Fig 3-15

 

55°

45°

30°

Angle Sin Cos

0 0 1

30 0.50 0.87

45 0.71 0.71

55 0.82 0.57

60 0.87 0.5

90 1 0

Biomechanics

Hypotenuse = 100

82

57

71

71

87

50

Vector Resolution

Trigonometric How does angle change the composition?

51

 

Angle Sin Cos

0 0 1

30 0.50 0.87

45 0.71 0.71

55 0.82 0.57

60 0.87 0.5

90 1 0

Biomechanics

90° 60° 45° 30° 0°

Application to human movement

Resolve force into: Perpendicular force

Rotation

Parallel force Compression

Position dependent

52

perpendicular

parallel

Biomechanics Module

End of Biomechanics Module

Don’t forget to take the quiz

Biomechanics Module

53