Chapter 12: Fundamentals of Solids and Structural Applications of Solids

Molecular Definition: At the molecular level, solids consist of particles that are fixed in space relative to one another.
Force Transmission: When external forces are applied to a solid, these forces are easily transmitted from one particle to another throughout the structure.
Crystalline Structures: - Sodium Chloride (NaCl): These crystals are defined as being cubic in nature. - Copper(II) Chloride ( $CuCl_2$ ): These crystals are defined as being distorted octahedral in nature.

The Solid State: - Molecules are arranged in regular, repeating patterns. - Particles are held firmly in place but possess the ability to vibrate within a limited, confined area.
The Liquid State: - Molecules flow easily around one another. - They are prevented from flying apart by attractive forces existing between the particles. - Liquids assume the specific shape of the container they occupy.
The Gas State: - Molecules fly in all directions at great speeds. - Particles are so far apart that the attractive forces between them become insignificant.
The Plasma State: - This state occurs at the very high temperatures found in stars. - Atoms in this state lose their electrons. - Plasma is a resulting mixture of free electrons and nuclei.
Energy Progression: Moving from solid to liquid to gas to plasma represents a state of increasing energy.

Hardness: This is a measure of how resistant a solid is to scratching or indentation.
Density: A measure of mass per given volume that a solid possesses.
Melting Point: The specific temperature at which a substance changes its state from a solid to a liquid.
Boiling Point: The specific temperature at which a substance changes its state from a liquid to a gas.
Elasticity: The inherent ability of a material to return to its original shape and size after an external force has been removed.
Tension: The internal stress within a material caused by an applied force that pulls or stretches it.

General Density: - Density measures how tightly packed particles are within a substance. - Mass ( $m$ ): The amount of matter/stuff, measured in units such as kilograms ( $kg$ ) or grams ( $g$ ). - Volume ( $V$ ): The amount of space occupied, measured in units such as cubic centimeters ( $cm^3$ ), milliliters ( $mL$ ), cubic meters ( $m^3$ ), or liters ( $L$ ). - Consistency: For any given substance, the ratio of mass to volume remains the same.
Weight Density ( $WD$ ): - Density is sometimes expressed in terms of weight ( $F_w$ ) rather than mass. - The formula for Weight Density is expressed as: $WD = \frac{F_w}{V} = \frac{m \times g}{V}$
Laboratory Application: Determination of density often involves water displacement or calculating volume for regular shapes using the formula: $V = l \times w \times h$

Measurement of Elasticity: This property measures how much a body changes when a deforming force is applied and how effectively it returns to its original shape.
Inelastic Materials: Materials that do not return to their original shape after deformation are termed inelastic; they remain permanently deformed.
Elastic Limit: Every material possesses a specific threshold of force where it can no longer bend or deform and return to its original state. This threshold is known as the Elastic Limit.
Examples: A baseball bat is considered to have elastic properties, as seen in high-speed captures of impact yielding recovery of shape.

Behavior under Force: Applying force to a solid differs from applying force to a gas or liquid.
Compression: This occurs when particles are squeezed together due to an applied force.
Tension: This occurs when particles are pulled apart due to an applied force.
The Neutral Layer: In a material under stress, the neutral layer is the region that experiences neither tension nor compression.
Material Specifics: - Steel: Excellent at handling both compression and tension. - Stone: Excellent at handling compression but poor at handling tension (prone to cracking/fracturing).

Girder Orientation and Stress: - In certain bending scenarios, a girder may experience tension on the upper side and compression on the lower side. - In reversed bending scenarios, the girder experiences compression on the upper side and tension on the lower side.
The I-Beam: - Solid beams and I-Beams exhibit the same tension and compression characteristics at their outer surfaces. - Because the neutral layer (the center) does not respond to compression or tension, that material can be "scooped out." - This results in a beam shaped like the letter "I." - Advantages of I-Beams: They weigh less, utilize less material, and require less labor for installation without sacrificing structural integrity.

Pole Vault Poles: Modern poles are hollow (transitioning from 1912 designs to 2020 technology) to optimize weight and flexibility.
Arches: - Historical buildings often required many supporting columns to hold up roofs. - The discovery of the arch allowed for the removal of these columns. - Arches utilize the natural capacity of stone to withstand compression. - This compression increases the overall strength and stability of the structure.