Physical Science
This domain tests matter, chemical and physical changes, motion and forces, energy transfer, and basic waves. Expect questions that require applying formulas, distinguishing similar concepts, and predicting motion from forces.
Matter and changes
- Atoms are the building blocks of elements; compounds are chemically bonded; mixtures are not chemically bonded.
- Physical changes alter state, size, or shape without changing substance identity; chemical changes form new substances.
- Conservation of mass means the mass of reactants equals the mass of products in a closed system.
- Density equals mass divided by volume; it is an intensive property that does not depend on sample size.
Forces and energy
- Newton's laws describe inertia, F = ma, and equal and opposite forces.
- Balanced forces produce no change in motion; unbalanced forces cause acceleration.
- Energy forms include kinetic, potential, thermal, light, sound, and electrical; energy transfers but is conserved in an ideal system.
- Waves transfer energy; for a fixed speed, frequency and wavelength are inversely related.
Worked example
A metal block has a mass of 54 g and a volume of 20 cm3. Density = mass/volume = 54 g / 20 cm3 = 2.7 g/cm3. Since 2.7 g/cm3 is close to the density of aluminum, the block may be aluminum, but density alone is not definitive because alloys or other materials can have similar densities. Reasoning: divide mass by volume and keep the units; density is a ratio, not the same as mass.
Traps that cost marks
- Confusing mass with weight; weight depends on gravity.
- Treating a state change as a chemical change.
- Adding forces in the same direction but ignoring opposite directions when finding net force.
- Mixing speed and velocity; velocity includes direction.
- Confusing heat with temperature.
- Assuming density changes when a sample is cut in half.