Week 2 Flashcards
What is a lever?
Any rigid segment that rotates around a fulcrum
When does a lever system exist?
Exists whenever two forces are applied to a lever in a way that produces opposing
torques
What are the components of a lever system?
- Effort force (EF)
- Resistance Force (RF)
- Effort Arm (EA)
- Resistance Arm (RA)
What is effort force?
Force that is producing the resultant torque(acting in the direction of rotation)
What is resistance force?
Force creating an opposing torque
What is the effort arm?
Moment arm for the effort force
What is the resistance arm?
Moment arm for the resistance force
The ___ force is always the winner in the torque game
The effort force is always the winner in the torque game
The first class lever is where the axis lies somewhere between the ____ and the ___
The first class lever is where the axis lies somewhere between the point of application of the effort force and the point of application of the resistance force
In the first class lever within the body, the effort arm may be ___ than the resistance arm as long as they are in ___ side of the axis
In the first class lever within the body, the effort arm may be equal to, greater, less than the resistance arm as long as they are in opposite side of the axis
The second class lever system, is where the resistance force has a point of application between the ___ and ____
The second class lever system, is where the resistance force has a point of application between the axis and the point of application of the effort force
In the second class lever system, the effort arm is always ___ the resistance arm
In the second class lever system, the effort arm is always greater than the resistance arm
The second class lever system, is where the effort force has a point of application between the ___ and ____
The second class lever system, is where the effort force has a point of application between the axis and the point of application of the resistance force
In the third class lever system, the effort arm is always ___ the resistance arm
In the third class lever system, the effort arm is always less than the resistance arm
What is the mechanical advantage?
Measure of the mechanical efficiency of a lever system or the relative effectiveness of the effort force in comparison with the resistance force
Mechanical advantage is related to the ___
Mechanical advantage is related to the classification of a lever
Mechanical advantage provides an understanding of the relationship between the ___ and ___
Mechanical advantage provides an understanding of the relationship between the torque of an external force and the torque of a muscular force
How is mechanical advantage calculated?
The ratio of the effort arm to the resistance arm
What is the mechanical advantage when the effort arm is greater than the resistance arm?
It is greater than 1
What happens when the mechanical advantage is greater than 1?
The magnitude of the effort force working through the larger moment arm can be smaller than the magnitude of the resistance force, yet still create greater torque
What is the advantage of mechanical advantage?
A smaller force can defeat a larger force
The mechanical advantage of a first class lever system in the body can be/is ___
The mechanical advantage of a first class lever system in the body can be/is greater than, less than, or equal to one
The moment arm of the muscle in a first class lever system within the body is ___ to the moment arm of the external force
The moment arm of the muscle in a first class lever system within the body is shorter to the moment arm of the external force
Muscles working at the first class lever system within the body tend to be at a ___
Muscles working at the first class lever system within the body tend to be at a mechanical disadvantage
The mechanical advantage of a second class lever system in the body can be/is ___
The mechanical advantage of a second class lever system in the body can be/is greater than one
The magnitude of the ___ can be, but is not necessarily less than the magnitude of the ____
The magnitude of the effort can be, but is not necessarily less than the magnitude of the resistance
The mechanical advantage of a third class lever system in the body can be/is ___
The mechanical advantage of a third class lever system in the body can be/is less than one
In the third-class lever system within the body, the effort arm is always ____ the resistance arm
In the third-class lever system within the body, the effort arm is always less than the resistance arm
The magnitude of the effort force must be ___ than the magnitude of the resistance force for the effort to produce greater torque
The magnitude of the effort force must be greater than the magnitude of the resistance force for the effort to produce greater torque
Why is a third-class lever system mechanically inefficient/working at a disadvantage?
The magnitude of the effort force must always be greater than the magnitude of the resistance force in order for the torque of the effort force to exceed the torque of the resistance force
What are the limitations of analysis of forces by lever systems?
- Discussion of lever systems ignored the established fact that the rotation of a lever requires at least one force couple
- Requires oversimplification that fails to take into consideration key elements that affect function and structural integrity
- Torques on human segments are not simply produced by muscles and external forces
True or false
An effort and resistance force are a force couple
False.
An effort and resistance force are not a force couple, because they move in opposite directions rather than the same
What are the 3 main methods of manipulating external forces to maximize torque?
- Torque of an external force can be increased by increasing the magnitude of the applied force
- Torque of an external force can be increased by applying the force perpendicular to the lever
- Torque of an external force can be increased by increasing the distance of the point of application of the force from the joint axis
A force applied to a lever produces its greater torque when the force is applied at ___ to the lever, presuming that there is a second part of the force couple
A force applied to a lever produces its greater torque when when the force is applied at 90 deg to the lever presuming that there is a second part of the force couple
What are the components of total force?
- Perpendicular component
- Parallel component
What is the perpendicular component of a total force?
The portion of a force that is applied at 90 deg to a segment
What is the parallel component of a total force?
The portion of a force that is applied at parallel to a segment
The parallel component of total force tends to create ___ motion
The parallel component of total force tends to create translatory motion
The perpendicular component of total force tends to create __ motion
The perpendicular component of total force tends to create rotation and horizontal translation motion
The sum of the magnitude of the perpendicular and parallel component of a force will always be ___ than the resultant force
The sum of the magnitude of the perpendicular and parallel component of a force will always be greater than the resultant force
The parallel component of most muscle forces contributes to ___, making muscles important joint stabilizers
The parallel component of most muscle forces contributes to joint compression, making muscles important joint stabilizers
Most of the force generated by a muscle contributes to joint compression rather than ___
Most of the force generated by a muscle contributes to joint compression rather than joint rotation
Rotation around a joint axis requires that the sum of the ____ equals zero
Rotation around a joint axis requires that the sum of the parallel and perpendicular components equals zero
What happens when the sum of the parallel or perpendicular components of a joint axis do not equal zero initially?
Translatory motion will continue to occur alone or in combination with rotatory motion until checked by a capsule ligamentous force or a joint reaction force
Majority of torque on a segment will be produced by forces or force components that are applied ___ to the segment and at some distance from the ___
Majority of torque on a segment will be produced by forces or force components that are applied 90 deg to the segment and at some distance from the joint axis
The greater the net unbalanced torque, the greater the ___
The greater the net unbalanced torque, the greater the angular acceleration of the segment
What is an open chain activity?
One end of a segment or set of segments is free to move in space
What are the characteristics of an open chain activity?
- Independent motion
- Allows isolation
- Typically non-weight bearing
- Mobility is greater than stability
- More functional in the upper extremity than in the lower extremity
What is a closed chain activity?
Both ends of a segment or set of segments are constrained in some way and are not free to move in space
What are the characteristics of a closed chain activity?
- Interdependent motion
- Shared load
- Typically weight bearing
- Stability is greater than mobility
- More functional in the lower extremity than in the upper extremity
What is stress?
Resistance of a material to deformation
What is strain?
Deformation that occurs in a material in response to the application of an external load quantified as a percentage of change in some dimension of the material
What are the characteristics of an isotropic material?
- Homogenous
* Exhibit uniform properties when loaded in different directions
What are the characteristics of an anisotropic material?
- Heterogenous
* Exhibit non-uniform properties when loaded in different directions
What is load?
Application of a force, moment, or combination of them to a material
What is tension?
Equal and opposite loads applied away from the surface of a structure
What is compression?
Equal and opposite loads applied toward the surface of a structure
What is shear?
Opposing loads applied parallel to the surface of a structure
What is torsion?
Opposing loads are applied to the surface of a structure resulting in twisting about an internal axis
What is bending?
Combination of three or more loads applied to a structure causing it to bend about an axis external to itself
When does combined loading occur?
Combination of two or more loading modes applied to a structure at the same time
What is deformation?
Change occurring in some dimension of the
material in response to an applied load
What is viscosity?
Ability of a material to resist flow and dampen shear forces
What is elasticity?
Ability of a material to return to its original shape following deformation after the removal of the deforming load
What allows meaningful movement of the human movement system to occur?
The articulations/joint of the skeletal system
What do human joints comprise?
Living tissues that change their structure to in response to changing environmental or functional demands
What are the 4 classes of connective tissue?
- Connective tissue proper
- Cartilage
- Bone
- Blood
____ are considered to be dense regular connective tissues
Tendons and ligaments are considered to be dense regular connective tissues
Connective tissue is characterized by…?
Widely dispersed cells and a large volume of extra-cellular matrix
___ is considered to be a highly specialized an mineralized form of connective tissue
Bone is considered to be a highly specialized an mineralized form of connective tissue
A microscopic levels, the extra-cellular matrix of connective tissues have both __ and ___ components
A microscopic levels, the extra-cellular matrix of connective tissues have both inter-fibular and fibular components
What determines the function of most connective tissue?
Extra -cellular components
The mechanical behavior of tissues involve the study of…?
The mechanical behavior of tissues involve the study of * how different materials and structures are able to provide support in response to changing forces*
The mechanical behavior of tissues deals with the relationship between ___ and ___
The mechanical behavior of tissues deals with the relationship between stress and strain
Stress occurs as a reaction force within…?
Stress occurs as a reaction force within the substance of the structure in the presence of an applied load
How can stress be quantified?
Force/unit area that develops within the material being tested.
What is ultimate stress?
The stress/load at the point of failure
What is ultimate strain?
The strain or deformation at the point of failure
What is isotropy?
A measure of the uniformity of the material when loaded from different directions
What is an example of an isotropic material?
Metals
What is an example of an anisotropic material?
Biological tissues
Which is more anisotropic: tendon, ligament, joint capsule, fascia?
Tendon more than ligament, joint capsule, and fascia
Tension results in…?
Tension results in lengthening and narrowing of the structure and causes tensile stresses to occur within the structure
What does compression result in?
Shortening and widening of the structure and causes compression stresses to occur within the structure
What does shear result in?
Internal angular deformation of the structure and causes shear stresses to occur within the structure
What does torsion cause?
A combination of compression, tension, and shear stresses to occur within the structure
What does combined loading cause?
Multiple combinations of stresses to occur within the structure
What is a load deformation curve?
A graph utilized to determine the strength properties and materials in which the load applied is plotted against the deformation material
What type of information does a load deformation curve provide?
Elasticity, plasticity, ultimate strength and stiffness, failure point, and the amount of energy prior to failure
What does the toe region of the load deformation curve signify?
Signifies the removal of slack within the structure as the tensile load is applied
What is a crimp?
A wavy configuration of collagen fibers found in most relaxed connective tissue
When does a crimp disappear?
When the collagen fibers in connective tissue are loaded
Where in the load deformation curve does a crimp occur?
In the toe region
What does the elastic region on the load deformation curve represent?
The range in which the stress is directly proportional to the strain
All the deformation occurring in the elastic region is ___
All the deformation occurring in the elastic region is reversible
Is the structure in the elastic region able to return to its normal dimensions after the load has been removed?
Yes, structures in the elastic region are able to return to its normal dimensions after the load has been removed
What does the elastic limit/ yield point signify?
The end of the elastic region where the material begins to undergo permanent deformation
What does the plastic region on the load deformation curve represent?
The range in which materials begin to deform at a rate disproportional to the stress
What is occurring in the plastic region?
Permanent deformation, although the structure is still intact and it may return to similar dimension with time
What does the ultimate failure point represent on the deformation curve?
Represents the continued load in the plastic range, but the maximum load that the tissue can tolerate has been reached.
What is happening with deformation and load at the ultimate failure point?
Deformation continues until it fails and load equals failure load
True or false
Tissue size can affect response to loading
True
Increased cross-sectional area of a tissue means that the tissue can withstand ___ force at any given length
Increased cross-sectional area of a tissue means that the tissue can withstand more force at any given length
An increased cross-sectional area of a tissue leads to ___
Greater strength and stiffness
Does the elongation to failure and length of a tissue changes when the cross sectional area is increased?
No, it stays the same
What does an increased tissue length mean?
It means that it can elongate further under the same load of condition as a shorter tissue
What is the status of strength and stiffness when the tissue length has been increased?
- Strength is the same
- Stiffness is reduced
What is young’s modulus/modulus of elasticity?
The linear portion of the curve that occurs in the elastic region of the load deformation curve.
The ____ is the measure of stiffness or resistance to external loads
The modulus of elasticity is the measure of stiffness or resistance to external loads
The _____ is the measure of compliance to external load
The reverse of the modulus of elasticity is the measure of compliance to external load
What does it mean when the slope through the young modulus is steep?
The modulus of elasticity is said to be high
A high modulus of elasticity correlates with ___?
A high modulus of elasticity correlates with high stiffness, and low compliance
Ex: cortico tissue
What does it mean when the slope through the young modulus is gradual?
The modulus of elasticity is said to be low
A low modulus of elasticity correlates with ___?
A low modulus of elasticity correlates with low stiffness and high compliance
Ex: Adipose tissue*
What is the stress-strain curve?
Load-deformation curve in which load is expressed as load per unit area and strain is expressed as deformation per unit of length or percentage of deformation
What happens in the toe region of the stress-strain curve for collagenous materials?
There is very little force to deform tissue in straightening crimp
What happens in the elastic region of the stress-strain curve for collagenous materials?
Collagen fibrils are being stretched and are resisting applied force
____ reflects type of collagen, fibril size, and cross-linking among collagen molecules
The elastic region of the stress-strain curve for collagenous materials reflects type of collagen, fibril size, and cross-linking among collagen molecules
What happens when load is removed in the elastic region of the stress-strain curve for collagenous materials?
When the load is removed, structure will return to its pre-stressed dimensions, although this return will take some time
The level of loading in the elastic region of the stress-strain curve for collagenous materials includes ____ and typically extends to about ____
The level of loading in the elastic region of the stress-strain curve for collagenous materials includes stresses and strains that
occur with normal activities and typically extends to about 4% strain