The Stuff of the Universe: Matter and Its Properties
Material science is an interdisciplinary field that studies the properties of matter and their applications.
Physical vs. Chemical Properties
A physical property is a characteristic that can be observed or measured without changing the chemical identity of the substance. Examples: color, density, melting point, boiling point, hardness.
A chemical property describes a substance's ability to undergo a specific chemical change. Examples: flammability, corrosiveness, reactivity with acid.
Density
Density (ρ, rho) is a fundamental physical property defined as the mass of a substance per unit volume.
Formula: ρ = m / V
It is an intensive property, meaning it does not depend on the amount of the substance. A small iron nail and a large iron girder have the same density.
The SI unit for density is kilograms per cubic meter (kg/m³), but grams per cubic centimeter (g/cm³) or grams per milliliter (g/mL) are also common.
States of Matter
Solid: Particles are tightly packed in a fixed arrangement and have low kinetic energy. Solids have a definite shape and a definite volume.
Liquid: Particles are close together but can move past one another. They have more kinetic energy than solids. Liquids have a definite volume but an indefinite shape (they take the shape of their container).
Gas: Particles are far apart and move randomly and rapidly. They have high kinetic energy. Gases have an indefinite shape and an indefinite volume (they expand to fill their container).
Plasma: A state of matter similar to a gas in which a certain portion of the particles are ionized. It is the most abundant state of matter in the universe (found in stars).
Mechanical Properties
Hardness: A material's resistance to localized plastic deformation such as scratching or indentation.
Elasticity: The ability of a material to deform under stress (like being stretched or compressed) and then return to its original shape when the stress is removed.
Plasticity: The ability of a material to undergo permanent deformation (a non-reversible change of shape) in response to applied forces. If you bend a paperclip, it has undergone plastic deformation.