Solids and Fluids

1
Solids and Fluids

• States of Matter
• Deformation of Solids
• Density and Pressure

2
Familiar States of Matter

• Solids atoms held together by electrical forces
• Crystalline has ordered structure (a)
• Amorphous has random structure (b)
• Liquids forces do not keep atoms/molecules in
  fixed positions and they can wander (c)
• Gases molecules in constant random motion,
  widely separated, and only exert weak forces on
  each other

Fig. 9.2, p. 269
3
Exotic States of Matter

• Plasma like a gas but electrons are separated
  from atoms
• Dark Matter invisible, inferred from motion of
  stars orbiting centers of galaxies
• Dark Energy invisible, one explanation for
  rapid expansion of universe

4
Deformation of SolidsStress and Strain

• Stress is the force per unit area causing
  deformation
• Strain is a measure of the amount of deformation
• For small stresses, stress is proportional to
  strain

Fig. 9.4, p. 271
5
Youngs Modulus Elasticity in Length

• Force is perpendicular to area A
• Force is tensile produces tension
• Tensile strain is ?L/L0
• Force per unit area has units of pressure (Pa)
• Y is Youngs modulus

Fig. 9.3, p. 270
6
Shear Modulus Elasticity of Shape
Fig. 9.4, p. 271

• Force is parallel to area A
• Force produces shear stress
• Shear strain is ?x/h
• S is Shear modulus

7
Bulk Modulus Volume Elasticity

• Force uniformly applied to all sides
  (perpendicular)
• Volume stress is ?P?F/A
• Volume strain is ?V/V
• B is Bulk modulus
• B is always positive
• Compressibility is B-1

Fig. 9.6, p. 272
8
Density and Pressure

• Density is mass divided by volume
• Specific gravity is ratio of density to density
  of water
• Pressure is force per unit area
• In a fluid molecules are free to move so it can
  not sustain a shear stress, only bulk stresses

9
Pressure Variation with Depth

• Fluid at rest in container
• All portions in static equilibrium
• All points at same depth at same pressure
• Consider shaded volume

Fig. 9.11b, p. 279
10
Pascals Principle

• A change in pressure applied to an enclosed fluid
  is transmitted undiminished to every point in the
  fluid and the walls of the container.

Fig. 9.14a, p. 281
11
Measuring Pressure

• Open tube manometer
• Gauge pressure is P - P0

• Barometer
• Gives atmospheric pressure P0
• 1 atm equivalent to 0.76 m of Hg

Fig. 9.16, p. 283
12
Archimedes Principle

• Buoyant force is equal to the weight of fluid
  displaced by an object

• Objects less dense than fluid rise (a)
• Objects more dense than fluid sink (b)

Fig. 9.19, p. 286
13
Totally Submerged Objects

• Examine Newtons 2nd Law

14
Floating Objects

• Examine Newtons 2nd Law

Fig. 9.20, p. 286