Natural Sciences: Physics, Chemistry, and Biology
Core concepts
Physics: Newton's three laws, speed/velocity/acceleration, work–energy–power, Ohm's law (V = IR) and simple series/parallel ideas, basic optics (reflection, refraction) and heat transfer. Chemistry: atomic structure (protons, neutrons, electrons), the periodic table trends, ionic vs covalent bonding, balancing equations and the mole idea, acids/bases and pH, and common reaction types. Biology: cell structure (plant vs animal), photosynthesis and respiration, genetics (dominant/recessive, DNA), human body systems (circulatory, digestive, respiratory), and ecology (food chains, energy flow).
Traps to watch
- Mass is not weight: mass is in kilograms, weight is a force in newtons (W = mg).
- Series vs parallel circuits: current is the same in series; voltage is the same across parallel branches.
- Balancing equations: atoms must balance, but you may never change subscripts - only coefficients.
- Photosynthesis vs respiration: they are near-reverses; plants do both, and respiration happens day and night.
- Energy in food chains decreases at each level (roughly a tenth passes on), so top predators are few.
Rule of thumb: identify the system
For any physics question, name the object, list the forces or quantities acting on it, then apply one law. For chemistry, count atoms on both sides before anything else.
Worked example
A 2 kg object accelerates at 3 m/s². Net force? F = ma = 2 × 3 = 6 N. If instead it hangs at rest, its weight is W = mg ≈ 2 × 9.8 = 19.6 N - a different quantity entirely.