Basic Biomechanics Flashcards
Biomechanics involves the study of? 2
Statics and Dynamics
Define statics:
Study of forces acting on rigid bodies in equilibrium or at constant velocity
What are the 3 subtypes of dynamics?
Kinetics
Kinematics
Kinesiology
Define kinetics
Study of forces acting on a rigid body and resultant motion
Define Kinematics?
Study of motion of a rigid body with no concerns of the forces
What is Newtons first law?
Inertia - a body in motion will remain in motion at a constant velocity in a straight line. Sum of external forces = zero
What is newtons second law?
Action
F = ma
Useful for dynamic analysis
A body with a non-zero net force will accelerate in the direction of the force
What is newtons 3rd law?
Reaction
What is a moment of force?
The effect of a force at a perpendicular distance from an axis - results in rotational movement and angular accelaration
Definition of energy?
Ability to do work
What is potential energy?
Ability to do work due to body position
What is kinetic energy?
Work required to stop/move a body
What is the working length?
Unsupported length of construct = length btw most distal point of prox fixation and most prox point of distal fixation
What is moment of inertia?
Second moment area/ Area moment of inertia
Ability of a structure to resist deformation - related to bending rigidity
What is polar moment of inertia?
Ability of an object to resist torsion
Definition of power?
Work/time
What are degrees of freedom?
Number of independent modes of motion in a joint
What is the relationship between DOF and constraint forces?
For every 1 DOF = 2 constrain forces
What is a 1st class lever?
Head
Atlanto occipital joint
Fulcrum in middle
What is a 2nd class lever?
Foot
Fulcrum on one side
Load then action force
What is a 3rd class lever?
Elbow
Fulcrum on one side
Action force then load
Define a lever?
Rigid structure that turns around a fixed point
How are bending forces calculated?
Force x distance from neutral axis over moment of inertia
MOI of a rectangular object =
(width x height) to 3rd power
wh cubed div 12
What is bending rigidity =
MOI x Young’s modulus
What is the MOI of a solid cylinder =
radius power of 4
pi x radius ^4 div 4
What is the MOI of hollow cylinder?
Radius^4 minus inner diameter ^4 div 4
How are shear stresses calculated?
Force x distance from axis of twist div polar moment of inertia
How is the torsional rigidity calculated
PMA x shear modulus
Polar moment of inertia of a solid rod =
pi r^4 div 2!!!
Polar moment of inertia of a hollow rod =
pi r^4 - I^4 div 2
