Biomechanics Exam 1
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This 6 page Study Guide was uploaded by Gianna Rossi on Saturday September 24, 2016. The Study Guide belongs to 3337 at Temple University taught by Dr. Tonia Shieh in Fall 2016. Since its upload, it has received 4 views. For similar materials see Comparative Biomechanics in Biology at Temple University.
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Date Created: 09/24/16
Biomechanics Exam 1 Study Guide History • Giovanni Borelli is the father of biomechanics • Marey invented the chronophotographic gun (multiple photos on a single frame) • Stop-‐Motion Photography invented by Eadweard Muybridge who also thought of the zoopaxiscope (multiple picture at high rate to create a video like stream) by betting on horses’ aerial phase Basic Terms to Know: • Extensibility • Work of Extension • Young’s Modulus (stiffness) – slope of a line in a stress strain curve, increases with extension • Stiffness • Brittleness • Strength • Resilience • Work of Fx • Toughness • Velocity: (has direction and magnitude AKA a vector) • Scalar: (numerical, speed) Central Pattern Generator (CPG’s) • Bundle of nerves (e.g heart SA node – pace maker) Control Mechanisms • Proximo-‐distal gradient of control: to maintain stability you need to gain control of center of mass. (e.g. seen in the birds that do not change motor patterns while running on flat terrain or rough terrain) Physics Principles: Newton’s Laws: 1. A body stays at rest or in uniform motion in a straight line unless a force is applied to it. 2. Acceleration is proportional to the applied force and is in the same direction as the force. 3. When one body exerts a force on another, the second always exerts a force that is equal in magnitude but opposite in direction. Mass/Principle of Continuity: the rate at which mass flows past any point along a pipe must be the same as flow past any point. Momentum: always remains constant but when it increases it is the reason the guy standing on a hose (see slide from 9/2) is lifted out of the water. Work is done against a force ONLY when an object is moved a certain distance. Force can be applied but work is only done when there is distance. Stress the amount of force applied over a given area (stress = F/A, units Pa or Nm ) -‐2 it is omnidirectional (in every given direction) Strain is a fractional change in length or dimensions as a result of an imposed stress. Unitless! Formula = change in direction/ initial (length, area, or volume) Stress vs Strain curve: as stress or force increases as you strength or strain a material where it suddenly ends is the point of fracture. Elastic region is the region where the material is still fully recoverable, plastic region returns to a new point. Ultimate Strength: most stress you can apply to a material before it breaks entirely. Extensibility: ?? Work of Extension ??? Moment or torque forces that cause rotation review problems using this!!! Force • Things move by producing a force on the environment and accelerates in the opposite direction • Force is produced by oscillating appendages, so it is unsteady whereas movement may be smooth. • Vortices are formed through movement in fluids (spirals, cyclical) • Center of mass holds balance • Spring Mass Model: stores energy then springs up allowing for movement. Ø Propulsion releases stored energy Ø Braking is like compressing (elastic storage in the gastrocnemius tendon) Ø Kangaroos have a pentapedal gait; their energy use declines the faster they hop. Jellyfish trade-‐off • Good predation vs good performance • The larger jellyfish is better at capturing their prey, however, they are weak when it comes to speed and chasing their prey. The smaller jellyfish are quicker and more able to chase their prey & also get away from predators however due to their smaller morphology they are less likely to capture their prey. Materials: Characterization of materials: • Isotropic: behaves the same regardless of the force applied/ loading direction • Anisotropic: direction maters in regards to its resistance • Tensile materials resist pulling forces (tensile forces) Ø Protein silk Ø Collagen (protein) Ø Cellulose (polysaccharide) Ø Chitin (polymeric sugar) – insect shells • Pliant Materials: how much they deform and how well they recover to their original forms after removal of stress (refer to seahorses tail shape) Ø Abduction-‐ matter that allows scallops to open shells Ø Elastin_ elasticity in skin Ø Resilin -‐ insects? Ø Slugs are also an example of this. • Rigid Materials: resist stress with minimal deformation. All are composites, anisotropic (e.g. bones are not strong when it comes to twisting) • Flexural stiffness-‐ is an objects resistance to bending and can be calculated as young’s modulus (E) * the second moment of area (l). The further away the material lies from the neutral plate the more resistance the object has or it is stiffer. • *Advantages to J shaped curve (see lecture 9/9) • Euler Buckling – isotropic materials (rarely biological) it is often preceded by ovalization and usually depends on the restraints at the end of the column. 2 F = n π E I / L • Local Buckling – common in hollow or thin walled objects, depends on wall thickness (K). F = Kpio i(r -‐r) E Ri gets larger • Viscoelastic materials have time dependent properties, contains both viscous and elastic properties that are time and/or stress dependent. (e.g. silly putty) Ø Example: slug slime is made of polysaccharides and protein. It moves by pushing back on its mucus, but changes to a liquid beyond a critical yield stress. Types of Materials: • Bamboo has a bulkhead, which prevents ovalization; it is essentially a strong piece in the center of the stick. • Wood is a material that is stiff enough to avoid drooping, strong but flexible, tough enough not to shatter and light enough not to buckle. In trees, pre-‐ stressing the wood in tension occurs when dead cells pull on the tree. • Toughness – resists crack propagation, absorbs large amounts of energy without fracturing, can withstand both high stress and strain, has a greater work of extension. • Torsion – sheer and tension on the outside but compression on the inside. Problematic in man-‐made materials but advantageous in biological materials like the dandelion. • Wood and the behavior of trees ***research in book • Collagen not very stretchy but stores a lot of materials. E.g tendons, elastic storage in the gastrocnemius tendon. Most energy is returned to the system, if there was a larger area between the two lines on an energy curve that is more energy lost. • Bone – isotropic, but similar to wood mechanically. Must resist loading forces from movement and from muscles using them as levers. Constant remodeling. Ø Trabeculae form along primary lines of stress and remodel in response to repeated impacts to the bone. Ø Antlers – high strength, high work of fracture, low stiffness, low-‐density (low mineral content). Ø Anti-‐Crack propagation 1. In-‐plane crack deflection, out-‐of-‐plane crack twisting 2. Uncracked ligament bridging 3. Deflection around hyper mineralizes regions (osteons) Ø Mollusk shell nacre – composite: calcium carbonate plates glued together by a proteinaceous matrix, mostly minerals but much a composition of materials makes these shells tougher than the minerals alone. Shifting of the plates absorbs energy. Seahorses Square Tails (article by Michael Porter) • Seahorses are not the only animal with a square tail, however, they are the only square prehensile tails. • The twisting of the tails give them the ability to wrap them up even more. They have more ventral bending than dorsal. • Porter’s hypotheses: 1. Square tail enhances grasping abilities and crush resistance 2. Tail segment skew, ventral-‐dorsal overlaps, and plate size limit dorsal bending. 3. Square shape performs “better” than circular tail shape during deformations. • Types of Joints: Ø Gliding Ø Elastic connection Ø Peg and socket joint Ø Ball and socket joint Ø Spring strut • Square is more organized, less resistance to crushing and twists less than circular. • On a load to displacement graph, square shows a steeper curve indicating it is steeper. Muscles: Types of Muscles: 1. Cardiac: Myogenic (it can generate movement from within itself) and also neurogenic 2. Smooth Muscle usually myogenic (stomach, urinary ducts) however, also neurogenic (vessels, iris, walls of sperm ducts) 3. Skeletal • Muscle contraction is caused by sarcomeres changes length. Sarcomeres are made up of actin and myosin, these cause contractions but do not change length. • Muscles are made up of multiple motor neurons • Smaller motor units five finer muscle control Muscle Contraction: • Muscles move by doing work (measure in Joules) • Muscles exert a force and shorten by a distance (change in L) • Work per unit time equals the power produced by muscles (Watts, W) Power = work/ time – you must have rate or velocity (direction) otherwise you talk about force. • Work =force x distance Types of Muscle Contraction 1. Shortening: concentric (+ force) 2. Isotonic Contraction: force, tone is staying the same (-‐/0/+) 3. Isometric Contraction: no change (e.g. pushing against a wall) (0) 4. Eccentric Contraction: elongation (-‐) *Holding something steady is both isotonic and isometric All myosin heads can attach to actin Actin & myosin are NOT overlapping at all Too much overlap Based on muscled function The faster you go the lower the force We can increase the power with springs! Shape of the muscle affects: • Amount of contraction (distance) • Velocity (depend on the number of sarcomeres) • Force is a physiological cross sectional area (PCSA) • Power • Longer muscles have sarcomeres lined up next to each other or “in series” this allows them to contract at a greater distance and therefore give them a greater velocity, force and power.
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