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34 Cards in this Set
- Front
- Back
two main areas of mechanics
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statics (nonmoving systems)
dynamics (moving systems) |
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force
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push or pull action
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vector
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quantity having both magnitude and direction
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inertia
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property of matter that causes it to resist any change of motion
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Torque
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force to produce rotation
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friction
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developed by motion of two surfaces
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velocity
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speed
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Newton's Three Laws of Motion
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1. Law of inertia - object will stay at rest or in motion until a force overcomes it
2. Law of acceleration - the amount of acceleration depends of strength of force 3. Law of action/reaction - for every action there is an equal and opposite reaction |
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Linear external force
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two or more actions along the same line. Normal forces are compressive and tensile. Shear force causes more damage than normal forces (rug burn)
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Parallel external forces
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forces that occur in the same plane, in the same or opposite direction
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Concurrent external forces
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two more more forces act from a common point, but pull in different directions, yielding the net effect of resultant force
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external force couple
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two forces act in equal but opposite direction, giving turning effect (opening jar)
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Muscle torque is greatest when movement arm is at what position
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90 degrees
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What determines a muscle forces' magnitude?
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The number of active muscle fibers
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What produces stability of an object?
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When all torques acting on it are even
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How is the center of gravity determined?
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The position and relation to the earth
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Base of support
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The part of the body that is in contact with the supporting surface
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Line of gravity
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Imaginary vertical lien passing down through the COG toward center of the earth - should be in the middle of the BOS for greatest stability
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4 things that give greater stability
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1. Wider BOS
2. Greater mass 3. greater friction 4. when moving, focusing on stationary object rather than looking down at feet |
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Lever
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rigid bar that can rotate about a fixed point when a force is applied to overcome resistance
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Fixed point about which a lever can rotate
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Axis or fulcrum
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Force
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What causes a lever to move, usually muscles
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Resistance
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What must be overcome for motion to occur - includes weight of object being moved, gravity, external weight
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Three types of levers
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1. First Class
2. Second Class 3. Third class |
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First class lever
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F___________R
A Designed for balance: head sitting on C1 |
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Second Class Lever
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R_____________F
A best used for power: wheelbarrow, standing on tip toes |
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Third Class Lever
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___________F R
A Best for ROM - speed and distance. Most common in body, example is elbow flexion |
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A shortened resistance arm requires more/less force (carrying something close to your body)
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less
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More/less force is required when resistance is as close to axis as possible
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less
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2-joint muscles in which it's possible to obtain active and passive insufficiency
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1. Triceps
2. Biceps 3. Hamstring 4. Quads 5. Wrist flexors and extensors 6. Extrinsic finger flexors and extensors |
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Open Kinetic Chain
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Isotonic Movement or exercise in which the origin is fixed and the insertion moves. Occurs in every ROM
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Closed Kinetic chain
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Movement or exercise in which the origin is fixed and the insertion moves, such as pullups and pushups, situps, etc.
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Closed packed joint position
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Joints push together, such as standing, runnign squat
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Open packed joint position
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Where joints are pulled apart, such as leg lift
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