Jamshidi AA, PT1 1.1 Mechanics Mechanics – Branch of physics concerned with motion and deformation of bodies, which are acted upon by mechanical disturbances (forces) – Oldest of all physical sciences Engineering (or "Applied") mechanics – Science of applying the principles of mechanics – Concerned with the analysis and design of mechanical systems – Three main parts…

Jamshidi AA, PT2 1.2 Biomechanics (cont.) Biomechanics (cont.) -- why? – Has led to improvements of understanding of many physiological processes – Contributed to development of medical diagnostic and treatment procedures – Provided means to design and manufacture medical devices, surgical tools, aids for the handicapped – Suggested means for improving human performance in workplace and in athletics

Jamshidi AA, PT3 1.2 Biomechanics (cont.) Components of applied mechanics in biomechanics – Determine magnitude, nature of forces at joints and in muscles (statics) – Motion analysis, sports mechanics (dynamics) – Development of basic equations of biological materials and systems (mechanics of materials) – Investigation of blood flow in circulation, air flow in lungs (fluid mechanics)

Mechanics and Materials Forces Displacement Deformation (Strain) Translations and Rotations Stresses Material Properties

Jamshidi AA, PT5 Stress Stress (  ): internal resistance to an external load – Axial (compressive or tensile)  =F/A – Shear  = F/A (parallel or tangential forces) Units Pascal (Pa) = 1Nm 2 Axial Shear

Jamshidi AA, PT6 Strain Change in shape or deformation (  ) Absolute strain Relative strain –  L/L o

Jamshidi AA, PT7 Musculoskeletal forces the same forces that move and stabilize the body also have the potential to deform and injure the body

Jamshidi AA, PT8 A stress-strain curve for tendon Five distinct regions A.toe region B.linear region C.progressive failure region D.major failure region E.complete rupture region

Jamshidi AA, PT9 Toe region: there is little increase in load with lengthening Linear region: increased elongation requires disproprtionately larger amounts of stress. Microfailure of the tendon begins early in this region (2 to 6% strain). Region of progressive failure: the slope of the stress-strain curve begins to decrease, indicating microscopic disruption. The gross tissue appears to be normal and intact (6% strain). Region of major failure: The slope of the stress- strain curve now flattens dramatically. There is visible narrowing at numerous points of shear and rupture (6 to 12% strain). Region of complete rupture: The slope of the stress-strain curve falls off, indicating a total break in the gross tendon. (12 to 15% strain)

Mechanics and Materials Forces Displacement Deformation (Strain) Translations and Rotations Stresses Material Properties

Jamshidi AA, PT Basic Concepts Newtonian mechanics are based on: – Length (L; quantitative measure of size) – Time (T; concept for ordering flow of events) – Mass (M; quantitative measure of inertia, the resistance to change in motion, of matter)

Jamshidi AA, PT Basic Concepts Derived concepts: – Velocity (time rate of change of position) – Acceleration (time rate of increase of velocity) – Force (action of one body on another, or a mechanical disturbance or load) – Moment/Torque (quantitative measure of twisting action of a force on a body)

Jamshidi AA, PT13 Kinematics Description of the movement of the body, independent of the forces or torque that cause movement and include: Linear & Angular displacement Velocities Accelerations – Type of motion Translation: linear motion in which all part of a rigid body move parallel to and in the same direction as every other parts. Rotation: all points in the rigid body simultaneously moves in a circular path about some pivot point (axis of rotation).

Jamshidi AA, PT14 Kinetics Describe the effect of forces on the body. – Force: push or pull that can produce, arrest or modify movement. – Newton’s second law: quantity of a force (F) can be measured by product of the mass (m) multiplied by the acceleration (a) of the mass. Force is zero when the acceleration is zero. Kinetic analysis include: moment of force produced by muscles crossing a joint, the mechanical power flowing from muscles, energy changes of the body

Jamshidi AA, PT15 Musculoskletal forces Internal Forces: produced from structures located within the body. – Active force (stimulated muscle) – Passive force (ligament, capsule or intramuscular connective tissue, friction) External Forces: produced by forces acting from outside the body. – Gravity – Ground – External load – Physical contact

Jamshidi AA, PT16 Vector: a quantity that is completely specified by its magnitude and direction Factors required to describe a vector Magnitude: length of the arrow Direction: spatial orientation of the shaft of the arrow Sense: orientation of the arrowhead Point of application: where the base of arrow contact the body

Jamshidi AA, PT17 Vector: a quantity that is completely specified by its magnitude and direction. Factors required to describe a vector Magnitude: length of the arrow Direction: spatial orientation of the shaft of the arrow Sense: orientation of the arrowhead Point of application: where the base of arrow contact the body

Forces and Equilibrium

Newton's Laws

Jamshidi AA, PT Newton's Laws Newton's first law: –A body at rest will remain at rest; a body in motion will remain in motion –Bodies in motion will travel at constant velocity and in a straight line –Requires the sum of the forces acting on a body to be zero (thus, the body is in equilibrium) – SF = 0 – SM = 0

Jamshidi AA, PT21 Newton’s First Law LAW OF INERTIA Inertia is related to the amount of energy required to alter the velocity of a body The inertia within a body is directly proportional to its mass Center of mass is where the acceleration of gravity acts on the body (center of gravity) Mass moment of inertia of a body is a quantity that indicates its resistance to a change in angular velocity I = m X r 2

Jamshidi AA, PT22 Mass moment of inertia of a body

Jamshidi AA, PT23 Center of mass & Change of the Mass moment of inertia

Jamshidi AA, PT Newton's Laws (cont.) Newton's second: –A body with a nonzero net force will accelerate in the direction of the force –The magnitude of the acceleration is proportional to the magnitude of the force – SF = m * a –Thus, the first law is a special case of the second law

Jamshidi AA, PT25 Newton’s Second Law LAW OF ACCELERATION Linear motion: force-acceleration relationship ΣF = m X a – ΣF designate the sum of or net forces Rotary motion: torque-angular acceleration relationship ΣT = I X α – ΣT designate the sum of or net forces

Jamshidi AA, PT26 Impulse-momentum relationship F = m X v/t Ft = m X v Linear momentum = mass X linear velocity Linear impulse = force X time T = I X ω/t Tt = I X ω Angular momentum = I X angular velocity Angular impulse = torque X time Momentum: quantity of motion possessed by a body Impulse: what is required to change the momentum

Jamshidi AA, PT27 Impulse-momentum relationship ground reaction force as an individual ran A>B: forward momenum is decreased

Jamshidi AA, PT28 Newton's third law: –For every action, there is an equal and opposite reaction ("if you push against the wall, it will push you back") –The forces of action and reaction are equal in magnitude but in the opposite direction –Important for helping draw free body diagrams, and concept of "normal" force 1.4 Newton's Laws (cont.)

Jamshidi AA, PT29 Newton’s Third Law LAW OF ACTION-REACTION Every effect one body exerts on another is counteracted by an effect that the second body exerts on the first The two body intact is specified by the law of acceleration ΣF = m X a Each body experiences a different effect and that effect depends on its mass

Movement Analysis

Jamshidi AA, PT31 Movement Analysis Anthropometry : measurement of physical design of human body (length, mass…) Free body diagram : simplified sketch that presents the interaction between a system and its environment

Jamshidi AA, PT32 Free Body Diagram

Jamshidi AA, PT33 Basic Dynamics

Moments Forces applied at a distance from the center of rotation cause the body to rotate. F x

Jamshidi AA, PT35 Lever Systems Rigid rod fixed at point to which two forces are applied 1 st class 2 nd class 3 rd class Functions –  applied force –  effective speed RF R F FR

Jamshidi AA, PT36 Mechanical Advantage > or = or < 1

Jamshidi AA, PT37 Mechanical Adventage > 1

Jamshidi AA, PT38 Mechanical Adventage < 1

Jamshidi AA, PT39 Line of Force & Moment Arm

Jamshidi AA, PT40 Internal & External Torques Static Rotary Equilibrium

IUMSJamshidi PhD_PT41

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Jamshidi AA, PT44 Change in the Knee Angle

Jamshidi AA, PT45 Change in Moment Arm

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Jamshidi AA, PT47 USING A CANE

Jamshidi AA, PT48 Carrying Externa Load