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Chapter 12 Properties of Matter: Solids

Chapter 12 Properties of Matter: Solids. Nick Conklin Waynesburg University March 6, 2009. Phases of Matter. Liquid. Solid. Gas. Solids. What makes a solid… solid? Atoms are bonded together Ionic, covalent, metallic, Van der Waals’. Crystal. Amorphous. X-rays*.

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Chapter 12 Properties of Matter: Solids

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  1. Chapter 12Properties of Matter:Solids Nick Conklin Waynesburg University March 6, 2009

  2. Phases of Matter Liquid Solid Gas

  3. Solids • What makes a solid… solid? • Atoms are bonded together • Ionic, covalent, metallic, Van der Waals’ Crystal Amorphous

  4. X-rays* • Discovered by Röntgen in 1895 • High energy photons (light) • Wavelength: 0.1-100 Angstrom (10-8 – 10-11 m) • Similar to the distance between atoms • Sometimes they can travel between atoms *X-rays are NOT solid, but we’ll see why they are important on the next slide. First medical X-ray:

  5. X-ray Diffraction How do we know about the structure of crystals? X-rays Film d ~ 1 wavelength

  6. Diffraction Waves that travel through a small opening (around 1 wavelength) will bend in a characteristic way

  7. X-ray Diffraction Each crystal has a unique pattern based on it’s 3-D structure!!

  8. Question: • Which weighs more? • 1 lb of lead • 1 lb of water • 1 lb of air • They are the same

  9. So What’s the Difference? Some substances pack more “stuff” into a smaller volume. For example: • 1 lb lead → 40 cm3→(pack of gum) • 1 lb water→ 450 cm3 → (pop bottle) • 1 lb air → 375,000 cm3→(chest freezer)

  10. Extreme Elements Densest elements: - Iridium - Osmium Why so dense?

  11. “Neutronium” Neutron Star: Densest thing (that we know of) in the Universe!! ρ≈ 3.7х1017 kg/m3 1 tsp of “Neutronium” has the same mass as about 1,000 Empire State Buildings (5 x 1012 kg )

  12. Question: In which situation does water have the highest density: • A small fish bowl • A 55-gallon fish tank • A lake • All the same Interesting fact: Frozen water is less dense than liquid, allowing ice to float.

  13. Question: If I heat the air inside a balloon, how does that affect the density? • The density increases • The density decreases • The density stays constant

  14. Fitness Applications of Density • Muscle is more dense than fat: • Two people with the same weight might not be equally fit • Less dense bones are easier to break • X-rays help us see them

  15. Hooke’s Law • The force required to stretch a spring is proportional to the “stretchy-ness” Δx • k ≡ “spring constant” • larger value implies a stiffer spring Caution: “Hooke’s Law” is often stated as “F = -k Δx”, where “F” is the force exerted by the spring, instead of the force on the spring. The minus sign comes from Newton’s 3rd Law

  16. Elasticity • An object that deforms when a force is applied and returns to its original shape when the force removed is elastic. • Bow, steel beams • Objects that don’t return to the original shape are inelastic. • Clay, dough • The point at which an object no longer returns to its original shape is the elastic limit.

  17. Question: I pick up a 20 lb weight and it stretches my bicep tendon by 0.1 cm. If the maximum distance my tendon can stretch before (painfully) hitting the elastic limit is 0.3 cm, what is the maximum weight I can lift? • 30 lb • 40 lb • 50 lb • 60 lb • 80 lb Why?

  18. Tension and Compression Δx Δx Δx Tension Compression Shear Applying a force to an object (stress) causes a change in shape (strain) that obeys Hooke’s law.

  19. Elastic limit Stress Ultimate Strength Strain Elasticity Objects return to original shape if deformation is small enough. The point at which a deformation becomes permanent is the elastic limit or yield strength The point at which on object breaks is called its ultimate strength

  20. Tension and Compression • Some materials are very strong under compression, but not under tension • Concrete • Some materials are very strong under tension, but not under compression • Rope, steel cable • Some are good at both! • Steel

  21. Question: • Consider a diver on a diving board. What stress is acting on the board? • Tension • Compression • Shear • All of the above • None of the above

  22. Diving Board (Cantilevered Beam) Tension Shear Compression Neutral Layer: Not under tension or compression!

  23. Table (Simple Beam) Compression Tension Neutral Layer

  24. I-Beams • Solid steel beams are extremely heavy • I beams have part of the “neutral layer” removed to reduce weight • Almost as strong under tension/compression in one direction • Weaker in the opposite direction

  25. Question Which shape has the strongest strength/weight ratio for a stress (force) applied from ANY direction:

  26. Fitness Applications (Bone) From what we know about the “neutral layer,” why are bones are “hollow” in the center?

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