Biomechanics webinar 1

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Biomechanics Unit 1-2:

Biomechanics Unit 1-2 Dr. Adrian VanIngen

Newton’s Laws:

Newton’s Laws An object stays in a state of rest or moves in a uniform motion in a straight line unless acted upon by forces that change that motion. force = resistance = no movement force < resistance = no movement force > resistance = movement

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Acceleration of a body is proportional to the magnitude of the resultant forces acting on it and inversely proportional to the mass of the object. Acceleration = Force Mass Force is needed to slow down or speed up a moving object. A large mass requires more force than a small mass to attain the same acceleration.

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For each action there is an equal and opposite reaction between contacting objects. Forces = a quantity that accelerates or decelerates a mass. F = mass x acceleration (F = MA) Actions that accelerate an object. Actions that resist acceleration.

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Types of Forces : loads : force or forces applied to the outside of an object. Stress: forces that develop or are transmitted within a structure. Weight = Force = Mass x Acceleration Centrifugal Magnetic Hydrostatic

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Units of Force . Dyne (cm-gram-second) 1 Dyne = the force which in 1 second accelerates 1 gram mass to a speed of 1 cm/sec. Newton (meter-kilogram-second) 1 Newton = the force which in one second accelerates a mass of 1 kilogram to a speed of 1 m/sec. Poundal (foot-pound-second) 1 poundal = the force which in 1 second accelerates a 1 pound mass to a speed of 1 foot/second.

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Loads : A ny force or combination of forces that are applied to the outside of an object. External force as opposed to forces within an object or material. Types of loads : Tension: a force that pulls causing a stretching, separating or elongation deformation of a structure i.e. a tendon pulling on a bone. Compression: a force that pushes structures together producing a squeezing or compression deformation of a structure i.e. intervertebral disc.

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Shear: parallel but opposite forces producing a slicing or scissor-like action on a structure i.e. tearing or cutting a piece of paper, biting food with your incisors. Stresses: forces that develop or are transmitted within a structure. -load forces are transmitted into a structure producing forces called stresses. -within the structures stresses develop to resist loading.

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Types of stresses : Tension Compression Shear When any load is applied to an object, tension, compression and shear stresses occur in the object. Strain (deformation) - the physical or molecular deformation of a structure as a result of stresses within that structure.

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Types of strain: Tension = elongation, stretching, separation. Compression = squeezing, constriction, compression. Shear = cutting, tearing. Bending = curving, bowing, angling. On the concave side there are compression stresses. On the convex side there are tension stresses. Torsion = twisting, turning, rotational shearing. Rotational forces acting in a parallel but in opposite directions producing a twisting deformation.

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Mechanical Work: Work (W) = Force (F) x Distance (L) - Force acting over a distance - not a function of time - isometric exercise = no movement; force not acting over a distance. No mechanical work with isometrics. Power: Power (P) = Force (F) x Distance (L) Time Work done per unit time.

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MECHANICAL ADVANTAGE can mechanically change the effects of a force by using pulleys or levers FIXED PULLEYS used to change direction of force but not magnitude many fixed pulleys in body (bony prominences; surgically made pulleys) force is equal in each strand force in each strand is equal to the force of resistance

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MOVABLE PULLEYS changes the direction and magnitude of the force forces on the supporting strands of the system are less than the resistive force can be used in combination with fixed pulleys.