Lecture 4: Physics of the ?· Lecture 4: Physics of the Skeleton 1. Skull 2. Mandible 3. Hyoid Bone…

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Lecture 4: Physics of the Skeleton1. Skull2. Mandible3. Hyoid Bone4. Cervical Vertebra5. Clavicle6. Sternum7. Costal Cartilage8. Ribs9. Scapula10. Humerus11. Radius12. Ulna13. Carpal Bones14. Metacarpal Bones15. Phalanges of Fingers16. Thoracic Vertebra17. Lumbar Vertebra18. Sacrum19. Os Coxa20. Femur21. Patella22. Tibia23. Fibula24. Tarsal Bones25. Metatarsal Bones26. Phalanges of Toes

Kinds of Bones Tubular support bones (limbs, digits)

Cylindrical bones protect soft tissue (spine)

Plate-like bones (skull)

Hip and shoulder bones

Ribs Wrist/ankle Teeth Inner Ear

Bones Support the body Protect organs

Rib cage (lungs, heart, thoracic organs) Skull (Brain, eyes, ears) Vertebrae (Spinal chord)

Walking, lifting, manipulation Chemical storage (Ca) Hearing

Composition of BoneCollagen, Mineral Ca10(PO4)6(OH!)2,

water

Collagen makes bones flexible (elastic) Mineral makes bones rigid Water in interstitial spaces stores nutrients

Compact BoneSpongy Bone

(Trabelcular)

Strength of Bones

Compact Y = 1.8x1010 N/m2Trabecular Y = 7.6x107 N/m2

Tensile Strength (Stress) Compact T = 1.2x108 N/m2

Compressive StrengthCompact C = 1.7x1010 N/m2Trabecular C = 2.2x106 N/m2

Viscoelasticity: Short duration:increased Strength

120x106

100

80

60

40

20

0

Stre

ss (

N/m

2 )

0.0120.0080.0040Strain

Yield Point

Hookes Law

Tensile Strength

F=kDL F/A = YDL/L Y is Stress/Strain k = Y A/L

Elastic (Youngs) Modulus

Too Much Stress(or whats wrong with this picture?)

How Bones Break Compression

Tension

Shear

Bending

Torsion

Oblique - a fracture which goes at an angle to the axisComminuted - a fracture of many relatively small fragmentsSpiral - a fracture which runs around the axis of the boneCompound - a fracture (also called open) which breaks the skinGreenstick - an incomplete fracture in which the bone bendsTransverse - a fracture that goes across the bone's axisSimple - a fracture which does not break the skin

Deceleration

Kinetic Energy = 1/2 mv2

Work done by force = F.d

Deceleration Force F = 1/2 mv2/d

Bungee Jumping: mg(h+d) = F.d or F = mg (h/d+1) (if h=d, a = 2 gs)

Lethal Force: 150-200 g