kinetics 2009 lecture 2with torque joke not to post
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• What movement (or what position) is occurring in the right knee?
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• What surface term can be used to describe what you can see of the hand in this photo?
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• When performing the movement in the picture the head has moved:
• A.) Anterior• B.) Medial• C.) Posterior
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Kinetics
Study of Forces Associated with Movement
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Scalar Quantities• Can be measured by an instrument of scale;
they are static (no direction). Has magnitude only.– Time – Space– Mass– Speed – Temperature
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Vector Quantities
• Indicate movement; can be measured only at a specific point in time as it is constantly changing
– 1) magnitude
– 2) direction
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Tug of War
500 N 200 N 100 N 400 N 300 N
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Factors to Describe Vectors• Magnitude• Direction-
• Vertical=Y• Horizontal=X
• Sense/Polarity– Internal force=positive Y– External force=negative Y
• Point of Application- Where muscle inserts to origin
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Types of Motion
• Translation or Linear - object moves in a straight line - all points of the object move in the same direction at the same speed, distance, and time
• Rotation (Axial, or angular) - One point of the object is fixed and the remainder of the object moves in an arc around a fixed point.
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Resolution of Forces
• May have two forces acting in different directions in the same plane - can determine force by using the Pythagorean theorem.– a(squared) + b(squared) = c(squared)
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Resolution of Forces:Clinical Application
3 N
4 N
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Lever System
• Lever - rigid bar or structure that turns around a fixed point; representing the bones of the body
• Fulcrum – fixed point around which rest of bar moves; representing a joint axis
• Force - usually representative of a muscle
• Resistance - force that must be overcome by a muscle
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Lever Arms
• Force - labeled F
• Resistance - labeled R
• Force Arm - distance between the application of force and the fulcrum - labeled FA
• Resistance Arm - distance between the point of resistance and the fulcrum - labeled RA
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Torque
• Torque considered a rotary equivalent to a force
• Produced by levers - moves around a fixed point - the rotation makes an arc or circle
• Torque = Force x Force Arm or Resistance x Resistance Arm– measured in newton-meters or foot-pounds
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First Class Lever
• Fulcrum is between the force and the resistance (e.g. see saw)– Example is atlanto-occipital joint (head and neck)– Articulation is of the occipital condyles and superior facets of
C1–
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First Class Lever
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1st Class Lever
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1st Class Leverhttp://video.google.com/videoplay?docid=-
1013712987391348587&ei=y0KUSuyeM5qIqQLfvsy7Dg&q=atlanto+occipital+joint&hl=en
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Second Class Lever
• Force and resistance are on the same side of the fulcrum with the resistance between the fulcrum and the force (e.g. bottle opener)– Example is foot (standing on toes)
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Second Class Lever
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2nd Class Lever
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2nd Class Lever
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Third Class Lever
• Force and resistance are on the same side of the fulcrum with the force between the fulcrum and the resistance (most levers in the body are third class levers).
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Third Class Lever
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3rd Class Lever
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Match
• 1st class lever• 2nd class lever• 3rd class lever
• Fulcrum in the middle• Force in the middle• Fulcrum in the middle
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Mechanical Advantage
• Efficiency of a lever - efficient when a small force required to overcome a large resistance.– MA=FA divided by RA– Force Arm is greater than resistance arm then
MA is greater than 1– In third class levers, MA is always less than 1
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Mechanical Advantage
• If mechanical advantage is greater than one, then lever was built for force
• If mechanical advantage is less than one, then lever was built for speed.
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Law of the Lever
• Lever is in equilibrium and will not move if: F x FA = R x RA
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What class lever is this? What downward force must be exerted at F to balance the downward torques of R1 and R2?
R1F R2
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What class lever is this? What downward force must be exerted at F to balance the downward torques of R1 and R2?
F R1 R2
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What class lever is this? What upward force must be exerted at F to balance the downward torque of R? What is the mechanical advantage of
this lever?
FR
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What class lever is this? What upward force must be exerted at F to balance the downward torque of R? What is the mechanical advantage of
this lever?
FR
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What class lever is this? What upward force must be exerted at F to balance the downward torque of R? What is the mechanical advantage of
this lever?
F R
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What class lever is this? What upward force must be exerted at F to balance the downward torque of R? What is the mechanical advantage of
this lever?
F R
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Two Types of Musculoskeletal Torque
• External – Forces outside the body
• Internal – Produced by muscles, tendons, and other soft
tissue in the body
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Types of Musculoskeletal Torque
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Moment Arm
• Is the radius of the specific arc of motion.
• This line runs perpendicular from the line of force to the axis of rotation
• The moment arm or torque arm changes as the muscles contract and lengthen
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Changing Resistance Arms
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External Torque (Barbell)
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External Torque
IFSin A = a/c
Sin 30 degrees = a/.3m
Find A
• Moment Arm =
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External Torque
• Here it is!
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Internal Torque (Biceps)
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Internal Torque
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Moment Arm
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Internal and external Torque
• External torque will change throughout the range of motion as the length of the moment arm changes.
• Internal torque changes throughout the range of motion as the length of the moment arm changes! – Internal torque usually operates in response to
external torque and is affected by those changes.
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Muscle Contraction
• Defined - development of tension in the muscle
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Contraction versus Contracture
• A contraction is an action of the muscle
• A contracture is a pathological process where soft tissue has become physically shorter and restricts movement
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Isometric Contraction
• Development of tension in the muscle, however, no movement; Length of the muscle does not change and there is no movement at a joint
• Also know as a static contraction
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Isotonic Contraction
• Length of the muscle changes
• There is joint movement
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Types of Isotonic Contractions
• Concentric - is a shortening contraction; Length of the muscle shortens; Force is greater than the resistance
• Eccentric - length of the muscle lengthens; Also called a lengthening contraction; Resistance is greater than force
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Concentric Contraction
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Eccentric Contraction
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Forces on Musculoskeletal System