Physical Science
The Physical Science domain tests mechanics, energy, waves, electricity and magnetism, and the structure and reactions of matter. Questions often ask you to apply a relationship, balance an equation, or interpret a graph.
Core rules and concepts
- Newton's laws: no net force means no acceleration; F_net = ma; forces occur in equal and opposite pairs on different objects.
- Energy is conserved but transforms among forms; momentum is conserved in isolated systems. Power is energy per time.
- For waves, v = fλ. Sound needs a medium; light does not. Frequency sets pitch or color; amplitude sets intensity.
- Ohm's law: V = IR. Series circuits share current; parallel circuits share voltage.
- Atomic number = protons; mass number = protons + neutrons. Ionic bonds transfer electrons; covalent bonds share them.
- Chemical equations must balance because matter is conserved. The mole ratio from a balanced equation gives stoichiometric predictions.
Worked example
For 2H2 + O2 → 2H2O, how many grams of water form when 8 g of H2 reacts with excess O2? Molar mass of H2 is about 2 g/mol, so 8 g = 4 mol H2. The balanced equation gives 2 mol H2O per 2 mol H2, a 1:1 ratio, so 4 mol H2O forms. Water's molar mass is about 18 g/mol, so 4 × 18 = 72 g H2O. Excess O2 means H2 is the limiting reactant.
Traps that cost marks
- Confusing mass with weight, or speed with velocity.
- Forgetting to balance an equation before using mole ratios.
- Using the limiting reactant as the excess reactant.
- Mixing up series and parallel rules.
- Reporting a wave speed without matching units for frequency and wavelength.