Report

Chapter 18 Solids 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 Na+ Cl- Snowflake H2O Crystal Structures Made from Carbon: Fullerine Diamond Carbon Nanotube Graphite 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 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 Practice Questions: 1. Which has the greater density – 1 kg of water or 10 kg of water? Neither. They both have the same density 2. 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 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. 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 Elastic Limit Elastic Limit is the distance that a material can be stretch at which point it will not return to its original shape Practice Questions: 1. 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