Physics Lect 5

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Physics Lect 5
2011-01-09 22:21:24
Fluids Solids

Fluids and Solids
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  1. Density
    • ρ = m / V
    • m: mass
    • V: volume
    • * remember that density changes with compression because volume will change
  2. Specific Gravity
    • Makes density more intuitive
    • SG = ρsubstance / ρwater
    • ρwater: 1 g/cm3 or 1000 kg/m3
  3. Pressure
    • P = F / A
    • when an object is submerged: pressure is equal to the force felt on the object divided by the surface area
    • * remember that pressure is there regardless of if the object is, this just makes it more intuitive
  4. Fluids at Rest
    • Fluids are at rest when they are only experiencing a force perpendicular to its surface
    • P = ρgy
    • * remember that if the container is open you must add Patmos which is 101 000 Pa
  5. Pascal's Principal
    • Pressure applied to an incompressable fluid will be evenly distributed
    • a hydrolic lift utilizes this principal (F applied to smaller S.A. --> P trans --> since the larger S.A. is larger the F is greater on it (no change in work though so the distance is less)
  6. Archimedes Principal
    • an object submerged in water displaces a volume of fluid equal to its own volume
    • an object floating displaces a volume of fluid equal to its weight
  7. Buoyancy Force
    • Submerged: Fb = ρfluid V g
    • Floating: Fb = mgobj = mgfluid
    • Fraction Submerged: ρobj / ρfluid
  8. Center of Buoyancy
    • is the point were the center of mass would be if the object were uniformly dense
    • the actual center of the object
  9. Fluids in Motion - Types of Motion
    • 1) Random Translational - contributes to fluid pressure as in a fluid at rest
    • 2) Uniform Translational - shared by molecules at a given location
    • energy from these two types of motion can be converted back and forth
  10. How do real fluids compare to ideal fluids?
    • real have drag, viscocity
    • drag works at the fluid-object interface, therefore the greatest velocity will be at the point farthest from that interface
  11. Flow Rate
    • Q = A v
    • Q: volume flow rate
    • A: area
    • v: velocity
  12. Bernoulli's Equation
    • P + ρgh + 0.5ρv2 = K
    • the sum of these three terms is a constant at any point in the fluid
    • term 1: pressure
    • term 2: potential
    • term 3: kinetic
  13. As velocity increases, pressure
    • decreases
    • think of the bee swarm standing vs. running analogy
  14. Surface Tension
    • temp dependent - the higher the temp the weaker the surface tension
    • if the adhesive forces (to the container) are stronger than the cohesive forces (between molecules) the miniscus will be a 'U' shape
  15. Solids and Heat
    Typically expand when heated