Physical Science: Matter, Mixtures, and Fluids
What you must understand
Matter is anything with mass and volume. Know the difference between physical properties (density, melting point, color, solubility) and chemical properties (reactivity, flammability). Distinguish physical changes (state changes, dissolving, tearing) from chemical changes (new substance formed, often with heat, light, gas, or color change).
Classify matter: elements (one kind of atom), compounds (two or more elements chemically bonded in fixed ratios), mixtures (substances physically combined). Homogeneous mixtures look uniform (salt water, air); heterogeneous mixtures do not (sand and iron filings). Know separation techniques: filtration (insoluble solid from liquid), evaporation (dissolved solid from solution), distillation (liquids by boiling point), and magnetism (magnetic materials).
For fluids, understand density = mass / volume and buoyancy: an object floats if its density is less than the fluid's, sinks if greater. Know pressure = force / area, that pressure increases with depth in a fluid, and that fluids flow and take the shape of their container.
Traps to expect
Questions often treat dissolving as a chemical change - it is physical. Another trap is assuming a clear liquid is pure; it may be a solution. Watch for density problems where mass and volume are swapped, and remember that a larger object is not automatically denser.
Worked example / rule of thumb
A block has mass 60 g and volume 20 cm³. Density = 60 ÷ 20 = 3 g/cm³. Since 3 g/cm³ is greater than water's 1 g/cm³, the block sinks. Rule of thumb: compare density to the fluid to predict floating or sinking.
Key ideas
- Physical vs. chemical properties and changes
- Elements, compounds, and mixtures
- Homogeneous vs. heterogeneous mixtures
- Separation methods matched to mixture types
- Density, buoyancy, and pressure relationships