Solids, Liquids, and Gases

1. Solids, Liquids, and Gases

2. A 2nd Grade Poem Solids, Liquids, Gas Solids we bump into. Liquids we jump into. Solids can crash! Liquids will splash! Solids we can grab and grip, Not liquids – they drip. But air is a gas, Not solid like brass, Or liquids like juice, Air is all loose!!!

3. 1. Liquids • Definite volume • Indefinite shape – takes the shape of the container. • Flow, fluid, particles slip past one another. Low kinetic energy.

4. Adhesive Forces – attractive forces between particles of different substances. • Capillary Action – water rising in very small diameter tubes – the adhesive forces between the water and glass are stronger than the cohesive forces in the water. • Allows water to flow up the xylem of trees. Allows wax to flow up the wick! Gives the meniscus in glass containers.

6. Cohesive Forces – Attractive forces between the molecules in a liquid. • Surface Tension – cohesive forces of liquid particles at the surface – the forces pull the particles closer together.

8. Evaporation – particles at the surface of a liquid gain enough energy to “escape” the liquid state and become a gas. When this happens, the liquid left behind decreases in temperature. • Volatile Liquids evaporate quickly and easily.

9. 2. Gases • No definite shape or volume • Fills the container • Mostly empty space, can be compressed. • Particles are moving with incredible kinetic energy (very fast). • Gas particles move in random straight lines.

10. 3. Plasma • Gas like mixture of charged particles. • Particles have extreme kinetic energy that when they collide they tear the electrons off creating positive and negative charged particles. • When the electrons return to the nucleus, it gives back the energy in the form of light (electromagnetic radiation).

11. Plasma is the most common state of matter in the Universe - stars • Lightning causes plasma. • Also in neon signs, fluorescent bulbs, mercury/sodium vapor lamps, aurora borealis (northern), and aurora australis (southern).

12. 4. Solids • Definite shape and definite volume • Vibrate in place, high cohesive forces, low kinetic energy. • Crystalline Solids – particles form a geometric pattern called a crystal lattice. Table salt is an example. • Amorphous Solids – particles do not form any patterns. They are sometimes called false solids. Wax and glass are examples.

14. Ice – Most solids “shrink” when frozen. Water expands when frozen because the molecules line-up for the hydrogen bonding. This is why ice floats in water – it is less dense.

15. Water density is the greatest at 4ºC.

16. Elasticity – ability of a solid to return to its original form when external forces are removed. Springs are elastic. • Physical States.mov

19. 5. Thermal Expansion • Matter expands when heated. Particle motion increases and takes up more volume (space). • Examples: • Concrete roads/sidewalks crack when it is heated so they leave expansion joints. • Bricks have holes. • Bridges have joints • Railroad tracks have gaps • Welders will cool rivets so they will fill in the holes and then expand making a tight fit.

22. The amount of expansion depends on the type of material. • Coefficient of Linear Expansion -  • Units are • Thermal expansion is proportional to the increase in temperature. • L = Li T • Lf – Li = Li (Tf – Ti) • Lf = Li + Li (Tf – Ti)

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24. Expansion can be in two directions (Area) or in three directions (Volume). • V = ViT •  - coefficient of volume expansion. •  = 3 • A = 2AiT

25. Problems • The coefficient of linear expansion of steel is 1 x 10-5/°C. How much expansion should engineers anticipate in a 2,000-ft steel bridge if it undergoes a change in temperature from 0°C to 30°C?