Force
what is always touching an object
gravity
what do Capsuloligamentous forces oppose
Gravity composition forces
what is shear force
any force that has an action line parallel to contacting surfaces that creates (or attempts to create) movement between surfaces. (think friction, p21-22)
What is a structure that acts to redirect a force without changing its magnitude called
a pulley
what does a force applied through the axis create
tension
composition of forces helps to find...
center of mass
what is joint distraction
Pulls one segment away from the other, creates tension in capsuloligamentous structures crossing a joint
what is joint compression
two forces that cause joint reaction forces on each segment (push of hand under leg-foot segment to knee extension p.20)
what is the perpendicular distance between an applied force and the axis of rotation called
moment arm
A muscle pulling on its tendon represents a ________ force
tensile
what is an action/reaction pair
Equal in magnitude, opposite in direction, always on different but touching objects, never part of the same linear force system
what are tensile forces
Pulling or stretching of the capsule, force applied to same object ("tug of war") to keep equilibrium, opposite in direction, equal in magnitude, same linear force system - CANNOT be reaction pairs
What is the difference between kinematics and kinetics
Kinematics is mechanical motion of objects without reference to the forces that cause the motion, Kinetics is the study of forces
Rotation is ______ displacement
angular
what is a Parallel Force system
2 or more forces applied to same object
What are the 5 parameters of kinematics
Type of displacement, location of displacement, direction of displacement, magnitude of displacement, rate of displacement
what is the "advantage" to a lever with a mechanical advantage greater than 1
the larger lever arm of the effort force allows the magnitude of the effort to be less than the magnitude of the resistance with still "winning"; that is, the effort force can be smaller than resistance (doesnt have to be!)
if force is increased, what happens to moment arm and torque
if force is increased, moment arm is increased and torque is increased
Most muscles have a short moment arm. What is the advantage of this
they can go through a larger range of motion with less shortening
Angular acceleration happens when...
Torque is unbalanced
what are the 3 lever classes, describe and give an example
First Class: axis in middle of effort arm and resistance arm (triceps brachii over head *)
Second Class: axis of rotation at end followed by short resistance arm and long effort arm (none in the human body***)
Third Class: axis of rotation near the end followed by short effort arm and long resistance arm (biceps acting concentrically (effort) to flex elbow against resistance of gravity)
muscle fibers within a pennate muscle represent a ________ force system and have the potential to produce joint __________.
parallel, torque
what is mechanical advantage of a 1st, 2nd, and 3rd class lever
1st - cannot be inferred, must look at specific lever arms
2nd - always has mechanical advantage (more than 1) effort is father from axis than resistance force
3rd - never has mechanical advantage (less than 1) effort is closer to axis than resistance force
Most muscles pull a segment both perpendicular and parallel to the segment. This creates both _______ and ________, respectively
rotation; translation
what is total muscle force
resultant pull of all fibers ,concurrent force system