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Physics > 2) Elements of biomechanics > Flashcards

2) Elements of biomechanics Flashcards

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1
Q

Biomechanics

A

Studies the medical properties of living tosses and organs

The mechanical phenomena talking place in the body as a whole and in the organs

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2
Q

Degree of freedom

A

The sets of independent displacements or rotations that specify the displaced position and orientation of the system

The number of degrees of freedom of the body is equal to the number of independent displacement and rotations of the body.

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3
Q

Dof example 1

A

Unobstructed ridged body has 6 dof

3 transitional = along each axis

3 rotational = rotations around each axis

DRAWING

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4
Q

DOF example 2

A

An unobstructed material point has 3 translational dof

Eg: atom of mono atomic gas

DRAWINGS

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5
Q

DOF example 3

A

A rigid body that can only rotate around one axis and has one rotational DOF

DRAWING

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6
Q

DOF example 4

A

2 material points with ridges connection between them have 5 DOF
3 transitional and 2 rotational

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7
Q

Joints of the human musculoskeletal system

A

The elements of a mechanism are connected to each other at the joint, this can be fixed or kinematic

Bones of the human skeleton are connected to other bones at fixed or kinematic joints

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8
Q

Single axis, 2 linked system

A

When A is fixed B has one rotation DOF

Elbow joint and knee joint

DRAWING

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9
Q

Single axis, three linked system

A

When A is fixed, B had one rotation dof and C has 2 DOF

Joints of the hand- phalanges

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10
Q

Double axis, two linked system

A

Double axis joints allow links to rotate around two perpendicular axis.

Link B has 2 rotation DOF relative to A

Atlanto occipital joint
Provides rotation of the head from left to right and front to back

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11
Q

Triple axis, two linked system

A

Allows the links to rotate around 3 perpendicular axes.

Link B has 3 rotational degrees of freedom

An example of this is the ball and socket shoulder joint and hip joint

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12
Q

Leavers in the human body

A

The human musculoskeletal system consists of bones connect to each other at joints and muscles attached to bones by tendons

Biomechanics studies musculoskeletal system as a set of linked levers and forces applied to these levers

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13
Q

Levers

A

Lever is a rigid body that can roatate around a fixed axis (fulcrum) by forces being applied to it
Lever has one rotation DOF

W=load
F= effort
DRAWING

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14
Q

Equilibrium condition

A

The torques is the load M_w and of the effort M_f rotate the lever in opposite directions.

Equilibrium:
Sigma M_w= sigma M_f
If torque is positive

Sigma M_i= 0
If load and effort have different signs

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15
Q

First, second and third class lever

A

Equilibrium condition:

F1_f =W1_w

DRAWING X3

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16
Q

Work accomplished by levers

A

Input:
A_f= F1_f 🌑

Output:
A_w = W1_w 🌑

Mechanical advantage:

M= w/f = 1_f/1_w

DRAWING

17
Q

First class lever example

A

The skull:

The fulcrum is at the Atlanto occipital joint

The load, the weight of the front portion of the head, is applied in front of the joint

The effort of the muscle is applied behind the joint at the back of the skull

18
Q

Second class lever example

A

Bones of the middle ear

The fulcrum is the joint between the malleus and incus

The load is applied at the oval window and stapes

The effort is applied at the tympanum and malleus.

19
Q

3rd class lever example

A

The jaw

The fulcrum is at the tenpormandibular joint.

The load is applied at the teeth

The effort of the muscles is applied on both sides of the jaw

20
Q

3rd class lever example ||

A

The forearm when used for lifting

The fulcrum is at the elbow joint

The load is applied at the hand

The effort is applied at the radius

21
Q

Action of the muscle effort

A

The vector of the force F developed by the muscle can be resolved by 2 components- along the bone F1 and normal to the bone Fn.

The longitudinal component F1 =F cos(alpha) the points at the joints press the bones without causing rotation.

The normal component Fn=Fsin(alpha) generates rotation of bone around fulcrum.

22
Q

Action of muscle effort 2

A

Useful work for moving the load is performed only by the normal

Fn= Fsin(alpah)

The muscle performs more work when Fn is larger

23
Q

Movement of the body

A

Muscles are the active parts of the musculoskeletal system.

Muscles contract and apply effort to skeletal bones causing them to move

This results in movement of parts of the body

24
Q

Types of muscle contractions

A

Isotonic

The length of the muscle changes and the tension remains constant
LOAD MOVES

Isometric

The length of the muscle remains constant and then tension changes
LOAD DOES NOT MOVE

25
Q

Work and power

A

Work A
The energy spent for displacing a body S by a constant force F
A=Fs

Power P
The amount of work performed per unit of time

P= da/dt = Fv

26
Q

Dynamic work of muscles 1

Equation

A

The work performed at an isotonic contraction of the muscle is

Applied muscular force x change of the length of the muscle

27
Q

Dynamic work of the muscles

A

The maximum force exerted by the muscle is proportional to the cross section of the muscle

The maximum work performed by one contraction of the muscle is proportional to the volume of the muscle.

28
Q

Dynamic power

A

When walking the human body performs work for

  • repeated lifting of the body
  • acceleration and deceleration of limbs

Mass of body is 75kg

  • speed 5Kmh = 60w power
  • speed 7kmh = 200w power
29
Q

Dynamic power 2

A

When jumping (brief effort)

  • body mass 70kh
  • centre of mass lifted by 1m
  • thrust time is 0.2s

The power is 3.5kw

30
Q

Statics( postural) work

A

When the body supports a weight the muscle get tired

The load doesn’t move and no useful work is performed

Tiredness means that muscles perform work- static work

31
Q

Static work 2

A

The muscles perform small contractions followed by relaxations (isometric contractions)

This results in dynamic work being performed against gravity
Static work is essentially dynamic work

32
Q

Equilibrium of the body

A

The center of mass of the body is above the ball and socket fulcrum (hip joint) unstable equilibrium

The body doesn’t fall because the supporting muscles perform work to sustain the posture of the body

Physics (11 decks)

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