1. Chapter 18 Solids

2. Crystal Structure
The crystalline structure of many solids results from the repeating orderly arrangement of molecules or atoms to form a geometric shape
How the atoms or molecules align themselves depends on the type of molecule or atom
Snowflake
H2O
Na+
Cl-

3. Crystal Structures Made from Carbon:
Fullerine
Diamond
Carbon Nanotube
Graphite

4. Density Density – how tightly material is packed together.
Density = mass
volume
Density is not mass or volume alone. It is a ratio between the amount of mass per unit volume.
Water has a density of 1 gram/cm3

5. Specific Gravity
A standard measure of density is specific gravity which is the ratio of the mass (or weight) of a substance to the mass (or weight) of an equal volume of water.
Hydrometer – used for measuring the specific gravity of liquids

6. Practice Questions:
Which has the greater density – 1 kg of water or 10 kg of water?
Neither. They both have the same density
Which has the greater density – 5 kg of lead or 10 kg of aluminum?
Lead
3. Which has the greater density – 1 g of uranium or the planet earth?
Uranium
4. The density of gold is 19.3 g/cm3. What is its specific gravity?
19.3 g/cm3

7. Elasticity
Elasticity is the property of a body by which it experiences a change in shape when a deforming force acts on it, and by which it returns to its original shape when the deforming force is removed.
Materials that do not resume their original shape after being distorted are said to be inelastic.

8. By hanging a weight on a spring, we are applying a force to the spring
By hanging a weight on a spring, we are applying a force to the spring. It is found that the stretch is directly proportional to the applied force:
This relationship between force and stretch of a spring is called Hooke’s Law
F ~ x

9. Elastic Limit
Elastic Limit is the distance that a material can be stretch at which point it will not return to its original shape

10. Practice Questions:
A certain tree brance is found to obey Hooke’s law. When a 20-kg load is hung from the end of it, the branch sags a distance of 10 cm. If instead, a 40-kg load is hung from the same place, by how much will the branch sag? How about if a 60-kg load were hung from the same place? (Assume that none of these loads makes the branch sag beyond its elastic limit.
20 cm for a 40 kg weight
30 cm for a 60 kg weight
2. If a force of 10 N stretches a certain spring 4 cm, how much stretch will occur for an applied force of 15 N?
6 cm