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chapter9_updated - 10/29/2009 Chapter 9 Solids and Fluids...

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10/29/2009 1 Chapter 9 Solids and Fluids Matter : A collection of interacting particles (atoms, molecules, charged particles, etc) Fundamental states of Matter: - Solid - Liquid - Gas - Plasma Temperature high low
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10/29/2009 2 Have a definite volume, definite shape Useful model for solids: Spring and ball model - Sizes of atoms: ~ 10 -10 m Solids exist in two distinct forms - crystalline solid - amorphous solid Crystalline solids: Atoms have an ordered structure. Example: Quartz, salt, diamond Amorphous solids: Atoms are arranged almost randomly. Example: glass - Glass and Quartz are two forms of the same material, SiO 2 Has a definite volume; no definite shape - Pour some water into the glass, volume of the water remains the same, shape changes Exists at a higher temperature than solids The molecules “wander” through the liquid in a random fashion The intermolecular forces are not strong enough to keep the molecules in a fixed position
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10/29/2009 3 Has no definite volume; has no definite shape - can be easily compressed Example: - Air (gas of N 2 , O 2 , CO 2 , etc) - H 2 , He gas Molecules are in constant random motion The molecules exert only weak forces on each other; collide occasionally Average distance between molecules is large compared to the size of the molecules Gasses are stored in pressurized tanks The most abundant form of matter in the universe When gas heated to a very high temperature: - many of the electrons are freed from the nucleus - Result is a collection of electrically charged ions and electrons Plasmas exist inside stars Plasma TV
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10/29/2009 4 All of the above mentioned forms of matters are sometimes referred to as normal matters Normal matter About 5% of total matter in the universe Dark matter May be as much at 25% of total matter Dark energy Accounts for acceleration of the expansion of the universe May be as much as 70% of all matter Unfortunately, we still don’t know precisely what dark matter and dark energy are All solids are deformable Both size and/or shape can be changed by applying forces (If the applied force is small) When the forces are removed, the object tends to its original shape - elastic behavior If solid deform permanently, it’s called plastic deformation F F L
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5 Suppose same forces are applied to two cylindrical wires Will the amount of deformation (elongation) be the same? - Force alone is not a good measure Stress: force per unit area F F F F A F area unit per force stress A With the same applied stress, the amount of deformation depends on the size (length) of the solid Strain: Fractional deformation (dimensionless) The elastic modulus is the constant of proportionality between stress and strain F F
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chapter9_updated - 10/29/2009 Chapter 9 Solids and Fluids...

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