Physical Science
Physical Science combines chemistry and physics: atomic structure, periodic trends, bonding, reactions and stoichiometry, acids and bases, plus motion, forces, energy, waves, and electric circuits. Items typically ask you to predict products, balance equations, or apply a formula to a described situation.
Matter and reactions
- Atomic number = protons; mass number = protons + neutrons; isotopes differ in neutrons only.
- Elements in a group share valence electrons. Metals tend to lose electrons and form cations; nonmetals gain electrons and form anions; sharing produces covalent bonds.
- Conservation of mass requires balanced equations - adjust coefficients, never subscripts.
- pH below 7 is acidic, 7 neutral, above 7 basic; each unit is a tenfold change in hydrogen ion concentration.
Motion, forces, and energy
- Newton's laws: inertia; F = ma; equal and opposite action–reaction pairs on different objects.
- Weight = mg, distinct from mass. Work = force × distance moved along the force; power = work ÷ time.
- KE = ½mv²; PE = mgh. Friction converts mechanical energy into thermal energy.
Waves and circuits
- v = fλ for all waves. In series, current is the same and voltage divides; in parallel, voltage is the same and current divides. Ohm's law: V = IR.
Worked example
A 0.50 kg cart accelerates from rest to 4.0 m/s in 2.0 s on a frictionless track. Acceleration a = Δv/Δt = 4.0 ÷ 2.0 = 2.0 m/s², so net force F = ma = 0.50 × 2.0 = 1.0 N. The work done equals the change in kinetic energy: ½ × 0.50 × (4.0)² = 4.0 J. Checking by distance, d = ½at² = 4.0 m, and F × d = 1.0 × 4.0 = 4.0 J - consistent.
Traps that cost marks
- Confusing mass with weight, or newtons with kilograms.
- Balancing equations by changing subscripts.
- Mixing up which quantity stays constant in series versus parallel circuits.
- Using the diameter instead of the radius, or forgetting to square velocity in kinetic energy.