L19-20;C13 Flashcards
When is static equilibrium achieved?
This is achieved if the resultant external forces and torques acting upon an object is equal to zero
Static equilibrium according to Newton’s first law means:
The object is not accelerating
How are the resultant external forces and torques calculated?
By using vector compositions
What is a dynamic equilibrium?
Concept indicating a balance between applied forces and internal forces for a body in motion
We can treat a system as a _______ point in space and mathematically it has the same effect if you _________________________
Single, track every point in the body
_____ can be considered concentrated at the CoG when analyzing linear kinetics of motion
Mass
What happens when mass distribution within an object is not constant?
The CoG shifts in a direction of greater mass
What are the two methods that can be used to calculate the CoG in the human body?
- Reaction board methods
2. Segmental methods
Where are there heavier segments? What happens to the CoM?
There are heavier segments in the trunk area, the CoM is mainly near the trunk for this reason.
What does the term stability mean?
This is used to describe the ability of a system to withstand disturbance
_____ ______ stability is ______ stability and refers to the entire combination of segments stability
Whole body, postural
Load bearing capacity of musculoskeletal structures is classified as what kind of stability?
Joint stability
Explain the following:
Force torque perspective of stability
Mechanical energy perspective of stability
Force torque perspective: considers the amount of torque and force required to disrupt equilibrium
Mechanical energy perspective: considers the amount of mechanical work required to disrupt equilibrium
Explain the following force torque perspective terms and give example.
Stable equilibrium
Unstable equalibrium
Neutral equilibrium
Stable equilibrium- when large forces and torques are required to disrupt equilibrium position. Think of triangle on its base and being pushed over.
Unstable equalibrium- if very little force or torque is required to disrupt the current state. Think of triangle on its top balancing and being pushed
Neutral equilibrium- when an object has no tendency to move in one direction or other. Think of ball on flat leveled area. Doesn’t move or want to.
The higher up an object is, the more ______ energy it’ll have due to the equation Mgh
Potential
With respect to mechanical energy perspectives explain the following:
Stable equlibrium
Unstable equilibrium
Neural equilibrium
Stable equlibrium- when an object is in state of minimum potential energy
Unstable equilibrium- when an object has a state of maximal potential energy
Neural equilibrium- when a state of constant potential energy is applied
What are the five factors that influence stability of equilibrium?
- Mass of object
- Friction
- Size of BoS
- Height of objects CoM/Cg [more PE->Higher CG, decreases stability]
- Relationship of Cg and Bos
What force is the only force acting on bodies CG since its constantly changing?
Gravity
What is the inverted pendulum representing?
Postural sway
Angular velocity and angular acceleration of body are affected by changes in _______ between body weight and vertical ground reaction force
Distance
For larger perturbations, we use a ______ ______ which is used to increase BoS
Compensatory step
When is it easier to initiate a rotation?
When force is applied perpendicularly and as far away from AoR
1st class lever has: 2nd class lever has: 3rd class lever has
1st class lever has: force weight at equal ends and fulcrum in middle (force and weight producing same direction torques)
2nd class lever has: fulcrum at end, force at other end and weight near fulcrum (weight producing negative torque, force producing positive)
3rd class lever has: fulcrum at end, force near fulcrum, weight at end (weight producing negative torque, force producing positive)
Three conditions must be met in order to be in static equilibrium:
- Sum of all vertical forces acting on body=0
- Sum of all horizontal forces acting on body= 0
- Sum of all torques=0
