Angular Kinetics 1 Flashcards
What is torque
the tendency for an object to rotate about an axis caused by a force - a rotary force - the result of a force applied a certain perpendicular distance from an axis of rotation
What are other terms for torque
moment of force
moment
Can a force exist if the object isnt moving
yes
What is torque dependent on
the size of the force and where the force is applied
What is torque influenced by
- The line of action of the force (direction)
- Its point of application
its magnitude
What is the moment arm
the distance from an axis that a force is being applied
The axis of rotation can be ___ or ____
fixed or free
A fixed axis is a ____
A free axis is a ___
hinge
CofG
The ____ can indicate the line of action of the muscles
tendons
Is torque vector or scalar
vector
The same force will create a different torque depending on…
the position of the arm
In general we can determine the magnitude and direction of the moment about the joint by…
considering the external force line of action in relation to the joints we are interested in
A negative moment causing ….
a negative rotation
does muscle action and moments always coincide ?
no
but sometimes
What is the purpose of lateral trunk bending
to reduce the forces in the abductor muscles and hip joint during single leg stance
In normal early stance the line of action of the GRF vector passes ____ of the hip and generates _____. The Hip extensors opposes this with a…
in front
a hip flexor moment
hip extensor moment
When does posterior trunk bending occur
If the gluteus maximus is weak or paralyzed
With posterior trunk bending the line of action of the GRF passes ___ the axis of the hip and creates a _____ moment
behind
hip extensor moment
What is the centre of mass
The point on a body where all of the mass of the object can be concentrated
The average location of all the mass in a body
What is the centre of gravity
The point in a body system around which its mass or weight is evenly distributed or balanced and through which the force of gravity acts
In traditional anatomical position, the heigh of a human centre of gravity is…
55-57% of your standing height
How do you calculate the centre of gravity ?
the sum of all the masses times the radius, divided by the sum of all the masses
The centre of gravity is a…
point of balance
The force of gravity pulls down on all mass particles in the body, each element creates a _____ about the other elements
torque
The centre of gravity is the position where…
the torques created by all the elements are balanced
The total weight acts through the….
centre of gravity
What are three ways to determine the CoG of segments in humans?
- Reaction board change method
- Cadaver limbs
- Scanning techniques (photogrammetry, Dexa, MRI)
What are two downside to the reaction board method for determining centre of gravity
takes very long and is not very specific to different body parts
How does the reaction board method work for determining centre of gravity
sum all torques around pivot point, wince we can find the weight of the individual and have the scale reading
How can we determine the mass of CoG of different segments?
Reaction board + force plate - mass and CofG location. Calculate torque in different postures
How do photogrammetry, dual-energy X-ray Absorbtiometry and magnetic resonance imaging images can be…
segmented and then known values for fat, muscle and bones are used to determine body segment parameters
If you lift your left arm to your side you CoG…
.shifts to the left and moves up slightly
Why does your CoG shift
because you have changed the distribution of the weight in your body. You stil lhave the same amount of weight on both sides but the moment arm of the weight of your arm is greater than it was so the torque is greater as well. To balance out the extra torque the centre of gravity shifts to the left
For each limb movement the CoG of the entirebody shifts in the direction of….
that movement
What does how much the CoG moves depend on?
the weight of the limb that moved and the distance it moved (torque caused by the limb)
Are centre of gravity and centre of pressure the same??
NO
What is the centre of pressure
This is the point location of the vertical ground reaction force vector. It represents a weighted average of all the pressures over the surface of the area in contact with the ground
If one foot is on the ground, the net CoP lies…
within that foot
at different points in the walking cycle the GRF vector acts… and creates….
at the centre of pressure under one foot and creates a torque about the CoG
During quiet standing the movement of the COP moves…
in such a way to minimize the movement of the COG.
The CoP oscillates around the position of the CoG creating…
opposing righting moments
The ___ will move back and forth trying to keep the ___ within the base of support
COP
COG
When you apply force to an object anywhere but its centre of gravity the object will…
translate and rotate about its centre
A force not through the centre tends to cause… why?
a change in both the angular and linear motion of an object
Because the object will have tendency to rotate about its center of gravity
