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conditions of linear and rotary motion
kinesiology chapter 12 and 13
29
Physiology
Undergraduate 3
12/10/2013

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Term
Mechanical axis
Definition
Straight line connects midpoint of joints on either end
Term
Muscle angle of pull
Definition
Angle between line of pull and mechanical axis of bone
Term
Rotary component
Definition
perpendicular to lever
Term
Rotary component
Definition
parallel to lever
Term
Anatomical pulley
Definition
changes angle of pull
increases rotary component
patella
Term
Linear forces
Definition
same direction
Term
Concurrent forces
Definition
Act at the same point of application
But at different angles
Term
Parallel forces
Definition
Not in the same line
But parallel to eachother
Term
Eccentric force
Definition
a force whose direction is not in line with the center of gravity of a freely moving object or the center of rotation of an object with a fixed axis of rotation.
Term
Torque
Definition
Turning effect of eccentric force
Product of force magnitude and length of moment arm.
Term
Moment arm
Definition
Perpendicular to line of force
Distance to axis of rotation
Term
Torque modification
Definition
Change moment arm or force
Term
Muscle force vectors for torque
Definition
Rotary component produces torque
Stabilizing component acts along mechanical axis of bone
Term
Summation of torques results in...
Definition
Either: no motion, linear motion, or rotary motion
Term
Resultant torque
Definition
Sum of torques
Clockwise are negative
Counterclockwise are positive
Term
Lever
Definition
A rigid bar that can rotate about a fixed point when a force is applied to overcome a resistance
Term
Purpose of lever
Definition
Balance 2 or more forces
Favor force production
Favor speed and range of motion
Change the direction of the applied force
Term
Anatomical levers
Definition
Bones = levers
Joint = fulcrum
Muscle = force
Term
Three points on a lever
Definition
Fulcrum
Point of resistance
Point of force applied
Term
Effort arm
Definition
Perpendicular distance between fulcrum and line of force of effort
Term
Resistance arm
Definition
Perpendicular distance between fulcrum and line of resistance force
Term
First Class lever
Definition
Effort -> fulcrum -> resistance
Term
Second Class lever
Definition
Fulcrum -> resistance -> effort
Term
Third class lever
Definition
Fulcrum -> effort -> resistance
Term
Acceleration of rotating bodies
Definition
Torque = moment of inertia X angular acceleration
Term
Moment of inertia
Definition

Depends on:

Quantity of rotating mass

Distribution around axis of rotation

I = Σmr2, m = mass, r = perpendicular distance between mass and axis of rotation

Term
Inertia in human body
Definition
Body position affects mass distribution and therefore inertia
Term
Angular momentum
Definition

Tendency to persist in rotary motion

Product of moment of inertia and angular velocity

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