Biomechanics Lecture II

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Terms in this set (...)

Scalars
Info about magnitude: like mass, length, & temp.
Vectors
Info about magnitude & direction: like velocity & force.
Length of an arrow
Represents magnitude
Angle of an arrow
Represents direction
Global
Body positions & movements relative to the world
Local
Body-based system like cardinal planes & axes of the whole body.
Joint angles
Relative position between two segments
Kinematics
Study of motion
Translation
Sliding motion
Rotation
Spin about an axis
Position
Where an object is located eiither 2D or 3D
Displacement
How far an object moves in space over time and in which direction it moves. VECTOR quantity
Velocity
How fast an object moves over a time and in which direction it moves. VECTOR quantity
Acceleration
Rate at which velocity changes in space over time and in which direction in velocity changes.
Displacement formula
Velocity Formula
Acceleration formula
Kinetics
Study of the action of forces.
Force
push or pull on an object
Mass
quantity of matter in an object
Inertia
resistance to a change in motion
Rotational inertia
proportional to mass & the distribution of mass about the axis of rotation
Newtons 2nd law
force = mass x acceleration
Hook's law
Relationship between force & deformation for linear springs.
Deformation
F=kx
k-->the stiffness
x-->amount of deformation caused by the applied force
Newton
Unit of force
Newton's First law
Inertia --
with no net force, a body remains at rest or at constant velocity until a force acts upon it.
Newton's Third Law
Reaction --
For every contact force there is an equal and opposite reaction force
Torque
Force that tends to cause rotation about an axis
Torque formula
Muscle Force
Creates torque about a joint and applies force to a tissue
Static Analysis
No acceleration - can be movement but, stays at a constant velocity.
Dynamic Analysis
accounts for the presence of accelerations
Compression
Deformation caused by a pressing or squeezing force
Tension
Deformation caused by a pulling or stretching force
Shear
Deformation caused by a sliding force
Torsion
Deformation caused by a twisting force
Bending
Deformation caused by a combination of compression & tension forces.
Compression forces
Affect the concave side
Convex Forces
Affect the convex side.
Cantilever Bend
Forces being applied to the outside of the two end of the bone.
Bending Moment
Action of applied forces.
Stress
The internal resistance of a material to an external load.
(the intensity of the force)
Pascal
unit of stress
Normal or axial Stress
The intensity of internal forces acting perpendicular to a plane of cut.
Shear or tangential stress
Intensity of internal forces acting parallel to a plane of cut.
Strain
Amount of deformation of a material under load expressed as a ratio of its initial dimension.
Normal or axial strain
In the direction of the long axis-can either be lengthening or shortening deformation
When an object lengthens
The object's width usually decreases.
When an object shortens
The object's width usually increases
Shear strain
the distortion caused by shear stress.
Stress-strain diagram
Common tool used to examine the mechanical behavior of a material under load
Elastic Region
Where deformation is not permanent
Plastic region
Where deformation is permanent
Yield Point
beginning of the plastic region
Failure
point of ultimate failure of the tissue
Energy
the area under the curve
Viscoelasticity
Material exhibits properties of viscous fluids & elastic solids
Four characteristics of viscoelastic materials
1. Hysteresis
2. Strain-rate dependency
3. Creep
4. Stress-relaxation
Elastic Material
Deform instantaneously under applied load, and regain their shape instantaneously when the applied load is removed.
Response of viscoelastic materials
Depends on how quickly the load is applied or removed
Strain Rate Dependency
Viscoelastic materials have different stress-strain relationships when deformed at different rates.
Creep
Behavior is increasing strain under a constant load
Stress-relaxation
Behavior is a reduction in stress while at a constant length
Stiff vs. compliant
The slope of the linear region
Brittle vs ductile
Deformation in plastic region
homogeneous vs. heterogeneous
Comparision of mechanical behavior in different locations
Isotropic vs. anisotropic
Comparison of mechanical behavior when loaded in different directions.
Stiff
greater resistance to deformation at a given stress
Compliant
materials deform more easily at lower stresses
Brittle
Refers to the property of sudden failure without plastic deformation
Ductile
Materials exhibit a large plastic deformation before failure.
Homogeneous
Materials have the same mechanical properties/behaviors regardless of location.
Heterogeneous
Properties change depending on the location in the tissue examined
Isotropic
Mechanical properties are independent of the direction of loading
Anisotropic
mechanical properties change with direction of loading.
Material failure
Can occur from a single max load or repeated sub-max loads.
Fatigue failure
When failure occurs due to repeated sub-max loads