Module 1 Flashcards
Human movement is a combination of what types of motion
linear and angular motion
Difference between internal mechanics and external mechanics
internal - mechanical factors produce movement from inside the body (muscles ligaments)
external - mechanical factors affecting the body from outside (gravity, car accident etc.)
Idealized force vector. What is it and what does it do?
It is a single force vector that represents the NET effect of other vectors.
Meant to simplify computation and analysis.
(there are many muscle fibres in a muscle, and joints are not perfect hinges, they move positions constantly. These things can complicate calculations, Idealized force vectors simplify this)
Describe injury analysis
Describes forces acting on the body such as gravity, other objects impacting body, forces in muscle, tendons, ligaments, bones, etc.
What is the centre of mass?
- single point where mass is located on average (equally).
- Can be located outside the body.
The mass equivalent to the idealized force vector.
What is a moment of force vs moment arm.
Two ways to increase moment of force.
Moment of force is torque.
Moment arm is the perpendicular distance from axis of rotation to where force is applied.
(Same as torque arm or lever arm.)
Increase moment of force by increasing moment arm or increase magnitude of force.
Describe the positive direction of rotation of the three axes. (can use fingers)
(use right hand)
- Thumb points up = z axis - rotates towards self and to my right
- Index finger = x axis - rotates toward self and down.
- middle finger = y axis - rotates towards point of index finger and down
Describe equilibrium
when does it exist?
Is when forces and moments are balanced.
Exists when free body is at rest or when it is at a constant linear or angular velocity.
Describe pressure.
What is CoP
Explain which is worse, large force applied over a large area, or a small area?
Total force applied over total area that force is applied to.
CoP = centre of pressure - location of average of all forces acting on surface.
Large force applied over a small area increases pressure and is more likely to cause injuries.
diff between CoM and CoP
CoM is anywhere in 3D world.
CoP average of sum of downwards forces acting on ground
what is a vector
Quantity that has both magnitude and direction
define egocentric vs allocentric frame of reference
ego - frame from internal point of view (e.g. your head)
Allo - frame from external point of view
what does material mechanics look at?
Internal responses to externally applied loads
- stress/strain
- compression, tension, shear, bending
- viscoelasticity (viscous - synovial fluid, elastic - like band)
- material fatigue and failure.
define load and deformation and stress
what must you do before comparing
load - externally applied force
deformation - change in shape of a body when load is applied
stress - resistance developed by tissue when externally loaded. Force divided by cross sectional area normalizes load (so you can compare different cross sectional areas.
stress - must normalize load to compare
define strain
what must you do before comparing
deformation of tissue subjected to external load.
Includes: Shear, compression, and tension
can measure absolute strain and relative strain.
to compare must normalize elongation
stiffness vs compliance, and what does the force-elongation curve look for stiffer vs more compliant material?
stiffness - resistance to deformation
compliance - ability to deform (opposite of stiffness)
stiffer material have sharper force-elongation curve where force = x axis, and elongation is on y axis
what are the two major types of bones and significance in structure
cortical - compact, strong, 80% of bones weight
trabecular - spongy, make up interior of bones
what is plastic deformation vs elastic deformation
which type of bone is better at elastic deformation?
plastic - material does not go back to original shape (permanent change)
elastic - material returns to original shape
trabecular is better for elastic. cortical is better for stiffness and resisting force.
Describe the 3 properties of viscoelastic tissue
Hysteresis - energy is lost in the loading/unloading cycle (in the form of heat)
e.g. tendons, ligaments and muscles are subject to this
Creep response - tissue subjected to constant load continues to deform.
e.g. loss of height during the day.
Stress relaxation - tissue stretch maintained at a length will result in decreased stress
e.g. holding stretch become easier after initial loading
describe material fatigue and failure
materials subjected to repeated loads experience fatigue (not the same as exercise fatigue though).If graphed, the response to loading looks different every time.
When material no longer can no longer withstand forces, can get deformed permanently meaning failure.
