Physical Science
The Physical Science domain tests matter, atomic structure, chemical reactions, motion, forces, energy, waves, and electricity/magnetism. Middle-grades items emphasize relationships, conservation laws, and correct use of units rather than complex calculation.
Core rules and concepts
Matter is classified as pure substances (elements and compounds) or mixtures (homogeneous and heterogeneous). Density equals mass divided by volume. Physical changes alter form or state without new substances; chemical changes produce new substances, often with evidence such as gas, precipitate, color change, or energy change. The particle model explains solids, liquids, gases, and diffusion.
Atomic number equals protons; mass number equals protons plus neutrons. Isotopes differ in neutrons. The periodic table arranges elements by increasing atomic number; groups share valence electrons and similar properties. Metals tend to lose electrons, nonmetals gain or share, and bonding determines compound properties.
In reactions, reactants become products and mass is conserved; balance equations with coefficients, never subscripts. Exothermic reactions release energy, endothermic absorb it. Motion: speed = distance/time; velocity includes direction; acceleration = change in velocity/time. Newton’s laws relate net force, mass, and acceleration; forces occur in pairs. Energy is conserved and transforms among forms. Work = force × distance; power = work/time. Waves transfer energy; frequency and wavelength are inversely related.
Worked example
A 2.0 kg cart experiences a net force of 6.0 N to the right. Using F = ma, a = F/m = 6.0 N/2.0 kg = 3.0 m/s² to the right. If the net force doubles while mass stays the same, acceleration doubles to 6.0 m/s². If mass doubles while force stays the same, acceleration halves to 1.5 m/s². The reasoning is that acceleration is directly proportional to net force and inversely proportional to mass.
Traps that cost marks
Watch for mass versus weight, speed versus velocity, and the mistaken idea that balanced forces mean rest-balanced forces mean zero acceleration, so velocity is constant. Do not confuse phase changes with chemical reactions, or coefficients with subscripts when balancing. Energy is not “used up”; it transfers or transforms.