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Biomechanics > Bio 3 > Flashcards

Bio 3 Flashcards

1
Q

What is inertia

A

An objects resistance to changes in its state of motion

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2
Q

What is the one thing inertia depends on

A

Mass

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3
Q

An object with greater mass is more ________ to speed up, slow down, or change direction while moving linearly

A

Difficult

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4
Q

What does angular inertia depend on

A

Mass and distribution of mass relative to the axis of rotation

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5
Q

Moment of inertia symbol and unit

A

I
Kgm2

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6
Q

Radius of gyration symbol and unit

A

k
m

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7
Q

What is radius of gyration

A

Distance between axis of rotation and point at which an objects mass could be concentrated to keep the same angular inertia as the object had in to original shape

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8
Q

What are newtons laws of motion (angular version)

A
  1. A rigid object will remain in its current state of angular motion unless a net external moment is applied
  2. The change in angular motion (angular acceleration) of an object is directly proportional to the net momentum acting on the object, and inversely proportional to the objects momentum of inertia
  3. For every action there’s an equal and opposite rxn
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9
Q

Explain “a rigid object will remain in its current state of angular motion unless a net external momentum is applied”

A

-The object will not rotate if it was not rotating to begin with
-The object will continue rotating at a constant angular velocity if it was already rotating

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10
Q

What is momentum

A

The quantity of motion that a body/object has

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11
Q

Angular momentum symbol and units

A

H
Kgm2/s

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12
Q

T or F: in human movement, the moment of inertia is not always constant

A

T
-it can change as we alter the configuration of body segments

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13
Q

As moment of inertia increases, does angular velocity increase or decrease

A

Decreases

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14
Q

Give an example of moment of inertia increasing as angular velocity decreases

A

Charlottes turns w arms in=faster/more rotation

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15
Q

Why does a sphere accelerate faster than a ring

A

The sphere has the lowest radius of gyration (k) and moment of inertia (I)

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16
Q

Law of action rxn examples

A

Knee extension:
Vastus mm produce equal and opposite moments on the shank and thigh

Falling forward:
Circle arms forward to create a moment in the CCW direction creating a CW moment at the trunk

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17
Q

What is deformable bodies

A

Considers deformation when force is applied

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18
Q

Two types of forces

A

Internal and external

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19
Q

Internal forces

A

Act within system of interest
-holds musculoskeletal system together
-can result from external forces

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20
Q

External forces

A

Act on the system as a result of its interaction w surrounding environment
-affect internal structures

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21
Q

Why is it important to understand the mechanical properties of tissues and how they respond to forces

A
  • evaluating injury mechanisms
  • preventing injury
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22
Q

Unit for stress

A

Pa

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23
Q

What is axial direction

A

Tension/compression; stress acts perpendicular to analysis plane

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24
Q

What is transverse direction

A

Shear; stress acts parallel to analysis plane

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25
Q

What 3 types of stresses represent the principal stresses

A

Tensile
Compressive
Shear

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26
Q

What is tension (tensile stress)

A

Stress due to a force that pulls apart the molecules bonding the object together
-forces act perpendicular to analysis plane
-tensions causes the object to stretch in the direction of the external force

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27
Q

Example of tension (tensile stress)

A

Hanging from a bar -sprain, mm tears, dislocation

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28
Q

Compression (compressive stress)

A

Stress due to a force that pushes molecules of an object more tightly together
-forces act perpendicular to analysis plane
- compression tends to cause the object to shorten in the direction of the external force

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29
Q

Example of compression (compressive stress)

A

Push up
Bruising, crush fractures

30
Q

Shear stress

A

Stress due to forces acting parallel to analysis plane
-slides molecules of the object past each other
-changes the orientation of the sides of the object

31
Q

Example of shear stress

A

Rug burn
-blistering, dislocations, shear fractures

32
Q

Real life loading situations in the human body commonly involve what

A

-multiple stresses at the analysis plane
-varying stresses across the analysis plane

33
Q

What is bending & example

A

A combo of tension and compression causing an object to deflect in a curved shape
-trying to break a pencil
*stress would be applies in the middle

34
Q

What 3 things allow bones to withstand different types of loading situations

A
  1. Round in cross section
  2. More dense near perimeter
  3. Less dense near neutral axis
35
Q

What is torsion & example

A

Shear stresses acting in opposite directions causing object to deform by twisting
Ex: twisting ends of pencil in opposite directions

36
Q

Combined loads is when…

A

Tension, compression, shear, bending, and torsion are combined

37
Q

What is strain

A

Deformation in an object in response to loading, relative to its original length

38
Q

Linear strain

A

Produced by compressive or tensile stresses

39
Q

Shear strain

A

Produced by shear stresses

40
Q

External forces —> resisted by internal forces —> ?

A

Quantified by mechanical stress

41
Q

External forces —> deformation —> ?

A

Quantified by mechanical strain

42
Q

What are the two ways in which deformation is measured

A

Absolute terms
Relative terms

43
Q

Absolute terms

A

Change in length between original and deformed length

44
Q

Relative terms

A

Referred to as strain
- change in length between l0 and l relative to l0

45
Q

Are compression & tension + or -

A

Tension is +
Compression is -

46
Q

Deformable objects loaded in tension stretch and compress in what directions

A
  • stretch in axial direction
  • compress in the transverse direction
47
Q

Deformable objects loaded in compression and example

A
  • Shorten in axial direction
  • stretch in transverse direction
    Ex: intervertebral disk
48
Q

For strain:
Axial direction is __________ of the applied load
Transverse direction is ________ to the applied load

A

In the direction
Perpendicular

49
Q

Poissons ratio

A

Relationship between strains in transverse direction and axial direction

50
Q

What is elastic behaviour

A

When the stress strain curve is linear
-stretch increases proportionally to strain
-object stretches under a tensile force or shortens under a compressive force
-object returns to original shape when the force is removed

51
Q

What is young’s modulus and what is its symbol and unit

A

Relationship between stress and strain for a material
E
Pa

52
Q

If a material has a higher elastic modulus it means that…

A

Material is stiffer
-steeper slope of stress strain curve

53
Q

If a material has lower elastic modulus it means that…

A

Material is more pliant
-shallower slope of stress strain curve

54
Q

T or F: when a force exceeds a certain size, there will be permanent deformation

A

T

55
Q

Plastic behaviour

A

When the stress strain curve becomes non linear (curved)

56
Q

Yield point/elastic limit

A

Point at which further stress will cause plastic deformation
-object won’t return to original shape when load is removed

57
Q

Material strength

A

Max stress or strain a material can withstand before failure

58
Q

Yield strength

A

Stress at the elastic limit of the stress strain curve
-occurs at end of elastic region
-stresses beyond this point cause deformation

59
Q

Ultimate strength

A

Max stress the material can withstand
-stress at the highest point of the stress strain curve

60
Q

Failure strength

A

Stress where breakage/rupture occurs
-occurs at end point of stress strain curve

61
Q

Failure strain

A

Strain in a material when breakage/rupture occurs
-occurs at endpoint of stress strain curve

62
Q

Toughness

A

Ability of a material to absorb energy
- more energy is needed to break a tougher material
-represented by the area under the stress strain curve

63
Q

What is tissue composed of

A

Ground substance
Water
Minerals
Collagen (stiff, high tensile strength)
Elastin ( pliant and extensible)

64
Q

Isotropic

A

Same mechanical properties in every direction

65
Q

Anisotropic

A

Different mechanical properties depending on the direction of the force

66
Q

What can bone withstand

A

Compression
Tension
Shear

67
Q

Mechanical strength and stiffness is affected by what

A

Rate of loading
-stronger and stiffer if loaded fast
-weaker and less stiff if loaded slowly

68
Q

What can articulate cartilage withstand

A

Compression
Tension
Shear

69
Q

When cartilage is subjected to compressive forces, it exudes water which leads to what

A

-creep
- stress relaxation

70
Q

What is creep

A

Tissue loaded at a constant stress

71
Q

What is stress relaxation

A

Tissue is loaded at a constant strain

72
Q

Tendon and ligament characteristics

A

-high in tensile strength
-little resistance in compression or shear
- exhibit creep and stress relaxation
- stretch easily under low tensile stresses
- become more stiff under high tensile stresses

Biomechanics (2 decks)

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