Top 200 Secondary 4 Physics Vocabulary

Secondary 4 Physics vocabulary means knowing what a question means before choosing a formula. The 200 terms below explain measurement, motion, forces, energy, thermal physics, waves, light, electricity, magnetism and radioactivity. Each term has a short definition, followed by practical examples, a four-week revision plan and answers to frequent questions.

Singapore students taking 2026 GCE O-Level Physics use subject code 6091. The first 2027 Singapore-Cambridge Secondary Education Certificate (SEC) G3 Physics uses K323. These are separate examination years and subject codes. This glossary is independent learning material, not a prescribed list issued by SEAB; it also includes helpful extension terms that may go beyond assessable content for a given route.

Quick information:

Find 200 clearly defined words, arranged in ten navigable clusters rather than an alphabetical wall.
Learn the difference between closely related ideas, such as speed versus velocity and current versus voltage.
See original worked examples using units, equations, graphs and everyday decisions.
Use the four-week study and recall plan, then verify your own syllabus.

Top 200 Vocabulary for Secondary 4 Physics: Meanings and Concepts

Read each word alongside a picture, measured result, formula or experience. When a definition includes a condition, retain it: a conditional statement in science is not an inconvenient detail.

1. Measurement and practical science — terms 1–20

Measurements need units and sensible significant figures. Check the instrument before calculating; a systematically misread scale cannot be repaired by averaging.

physical quantity — A property that can be measured and expressed with a unit.
SI unit — A standard unit within the International System of Units.
base unit — A fundamental unit used to define other units.
derived unit — A unit formed by combining base units.
scalar — A quantity specified by magnitude only.
vector — A quantity specified by magnitude and direction.
magnitude — The numerical size of a physical quantity.
resolution — The smallest change an instrument can distinguish.
accuracy — Closeness of a measurement to an accepted value.
precision — Closeness of repeated measurements to each other.
uncertainty — An estimated range of possible measurement error.
zero error — An instrument offset when it should read zero.
parallax error — A reading error from an unsuitable viewing angle.
systematic error — A consistent bias affecting readings in one direction.
random error — Unpredictable variation between repeated measurements.
calibration — Checking an instrument against a reference.
independent variable — The factor deliberately changed in an experiment.
dependent variable — The measured response in an experiment.
controlled variable — A factor deliberately kept unchanged.
best-fit line — A representative trend line through plotted observations.

2. Motion and the language of graphs — terms 21–40

Distance and displacement answer different questions. A round trip can have a substantial distance and zero displacement.

distance — Total length travelled regardless of direction.
displacement — Change in position with direction included.
speed — Distance travelled per unit time.
velocity — Rate of change of displacement.
acceleration — Rate of change of velocity.
deceleration — Acceleration opposite to the direction of motion.
uniform motion — Motion with constant velocity.
instantaneous speed — Speed at a particular moment.
average speed — Total distance divided by total elapsed time.
average velocity — Total displacement divided by elapsed time.
time interval — Duration between two events.
distance-time graph — A graph displaying total distance against time.
displacement-time graph — A graph displaying position change against time.
speed-time graph — A graph displaying speed against time.
velocity-time graph — A graph displaying signed velocity against time.
gradient — The change in vertical value per horizontal change.
area under graph — A geometric area representing a physical quantity in some graph relationships.
free fall — Motion under gravity alone when air resistance is neglected.
terminal velocity — Constant velocity reached when forces balance.
reference frame — A chosen viewpoint for describing positions and motion.

3. Forces, moments and pressure — terms 41–60

A force can change velocity or shape. If the resultant force is zero, a moving object can continue at constant velocity rather than having to stop.

force — A push or pull capable of changing motion or shape.
resultant force — The vector sum of forces acting on an object.
balanced forces — Forces whose vector sum is zero.
unbalanced forces — Forces with a nonzero resultant.
inertia — Resistance of matter to a change in velocity.
mass — A measure of inertia, usually in kilograms.
weight — The force of gravity acting on a mass.
gravitational field strength — Weight per unit mass at a location.
friction — A force opposing relative sliding or tendency to slide.
air resistance — A drag force caused by motion through air.
normal contact force — A supporting force perpendicular to a surface.
tension — A pulling force transmitted through a taut string or cable.
moment of a force — Force times perpendicular distance from the pivot.
pivot — The point around which an object turns.
perpendicular distance — The shortest distance at right angles to a line.
centre of gravity — The point through which an object’s weight acts.
equilibrium — A state with zero resultant force and turning effect.
pressure — Normal force exerted per unit area.
density — Mass per unit volume.
upthrust — An upward force caused by fluid pressure differences.

4. Energy, power and useful work — terms 61–80

Energy is conserved, but useful energy may spread to the surroundings. Do not describe efficiency losses as energy disappearing.

energy — A conserved physical quantity transferred or stored in different forms.
energy store — A way energy is held within a system.
kinetic energy — Energy associated with motion.
gravitational potential energy — Energy associated with position in a gravitational field.
elastic potential energy — Energy stored in a stretched or compressed elastic object.
internal energy — Total microscopic kinetic and potential energy of a system.
work done — Energy transferred by a force acting through a distance.
power — Energy transferred or work done per unit time.
efficiency — Useful output energy divided by total input energy.
energy transfer — Movement of energy between stores or systems.
conservation of energy — Energy cannot be created or destroyed in an isolated system.
renewable resource — An energy source naturally replenished on useful timescales.
nonrenewable resource — An energy source depleted faster than it forms.
fossil fuel — A carbon-based fuel formed from ancient organic material.
nuclear fuel — A material used to release energy from nuclear reactions.
hydroelectric power — Electricity generated using flowing or falling water.
solar power — Energy harnessed from sunlight.
wind power — Energy obtained from moving air.
energy dissipation — Spreading energy to surroundings in less useful forms.
kilowatt-hour — An energy unit equal to one kilowatt used for one hour.

5. Particle model and heat transfer — terms 81–100

Temperature and thermal energy are not interchangeable. Use particle movement and material properties to explain heating, cooling and state changes.

kinetic particle model — A model explaining matter through moving particles.
solid — Matter with particles held in approximately fixed positions.
liquid — Matter with definite volume but no fixed shape.
gas — Matter that spreads to fill its container.
particle motion — Microscopic movement of constituent particles.
temperature — A measure related to the thermal state of a body.
thermal equilibrium — A condition with no net thermal energy transfer.
conduction — Thermal energy transfer through a substance without bulk flow.
convection — Thermal transfer involving bulk movement of a fluid.
radiation — Energy transfer by electromagnetic waves.
thermal conductor — A material through which thermal energy passes readily.
thermal insulator — A material that slows thermal energy transfer.
specific heat capacity — Energy needed to raise one kilogram by one kelvin.
specific latent heat — Energy per kilogram needed for a phase change at constant temperature.
melting — Change from solid to liquid.
freezing — Change from liquid to solid.
boiling — Formation of vapour throughout a liquid at its boiling point.
evaporation — Escape of particles from a liquid surface.
condensation — Change from gas to liquid.
expansion — Increase in dimensions often caused by heating.

6. Waves and wave measurements — terms 101–120

Waves move energy rather than carrying matter along with them overall. Match frequency and wavelength to the given medium and wave speed.

wave — A disturbance that transfers energy without net transport of material.
oscillation — A repeated motion about an equilibrium position.
amplitude — Maximum displacement from equilibrium.
wavelength — Distance between successive points in the same phase.
frequency — Number of oscillations per second.
period — Time for one complete oscillation.
wave speed — Distance a wavefront moves per unit time.
transverse wave — A wave with oscillations perpendicular to propagation.
longitudinal wave — A wave with oscillations parallel to propagation.
compression — A region of higher particle density in a longitudinal wave.
rarefaction — A region of lower particle density in a longitudinal wave.
wavefront — A line or surface connecting points of equal phase.
reflection — A wave bouncing back at a boundary.
refraction — A change in wave direction due to speed change at a boundary.
diffraction — Spreading of waves through openings or around obstacles.
superposition — Addition of wave displacements where waves overlap.
interference — A pattern of reinforcement or cancellation from overlapping waves.
resonance — Large response when driving frequency matches a natural frequency.
sound wave — A mechanical vibration travelling through a material medium.
echo — A reflected sound heard separately from its original.

7. Light, lenses and the electromagnetic spectrum — terms 121–140

The electromagnetic spectrum contains different wavelengths of the same kind of wave. The safety implications depend on the radiation and the exposure.

electromagnetic spectrum — The range of electromagnetic radiation frequencies.
radio wave — Electromagnetic radiation with relatively long wavelengths.
microwave — Electromagnetic radiation between radio and infrared bands.
infrared — Electromagnetic radiation beyond the red end of visible light.
visible light — The band of electromagnetic radiation detectable by human vision.
ultraviolet — Electromagnetic radiation beyond violet with higher frequency.
X-ray — High-frequency electromagnetic radiation used in imaging and research.
gamma ray — Very high-frequency electromagnetic radiation often from nuclear processes.
ray diagram — A drawing showing the idealised paths of light.
incident ray — A ray travelling towards a surface.
reflected ray — A ray leaving a reflecting surface.
refracted ray — A ray changing path across a boundary.
normal line — A line perpendicular to a surface at the point of incidence.
angle of incidence — Angle between an incoming ray and the normal.
angle of reflection — Angle between a reflected ray and the normal.
refractive index — A measure relating light speed in vacuum to speed in a medium.
critical angle — An incidence angle giving a refracted ray along the boundary.
total internal reflection — Complete reflection inside a higher-index medium above the critical angle.
converging lens — A lens that can bring parallel rays towards a focus.
focal length — Distance from a lens or mirror reference point to the focus.

8. Charge, current and DC circuits — terms 141–160

Current is a rate of charge flow, while potential difference is energy per charge. These units are why V = IR and P = VI carry meaning.

electric charge — A property responsible for electromagnetic interactions.
static electricity — Effects of electric charge at rest.
electric field — A region in which a charge experiences electric force.
current — Rate of flow of electric charge.
potential difference — Energy transferred per unit charge between two points.
electromotive force — Energy supplied per unit charge by a source.
resistance — Potential difference divided by current for a circuit element.
Ohm’s law — The proportionality between voltage and current at constant physical conditions.
resistor — A component used to provide electrical resistance.
series circuit — A circuit with components along a single current path.
parallel circuit — A circuit with branches sharing the same two junctions.
voltmeter — An instrument for measuring potential difference.
ammeter — An instrument for measuring current.
conductor — A material permitting charge to move readily.
insulator — A material resisting movement of charge.
fuse — A protective device designed to break a circuit at excessive current.
circuit breaker — A switch that interrupts a circuit under specified fault conditions.
short circuit — An unintended low-resistance path for current.
electrical power — Rate of transfer of electrical energy.
earthing — Connecting equipment to ground as part of electrical safety.

9. Magnets, motors and induction — terms 161–180

Induction requires changing magnetic conditions. A permanent magnet held still near a closed loop does not necessarily cause a continuous induced current.

magnetic field — A region where magnetic forces act on magnets and moving charges.
magnetic field line — A line showing direction of a magnetic field.
magnetic pole — A region of a magnet associated with strong magnetic effects.
permanent magnet — A material that retains substantial magnetisation.
temporary magnet — A material easily magnetised but not strongly retaining magnetism.
electromagnet — A magnet produced by current in a conductor or coil.
solenoid — A long coil that produces a field when current flows.
motor effect — A force on a current-carrying conductor in a magnetic field.
electromagnetic induction — Production of electromotive force by changing magnetic flux.
induced current — Current caused by an induced electromotive force in a closed path.
electromotive induction — Another expression for generation of electromotive force by changing magnetic conditions.
magnetic flux — A measure of magnetic field passing through an area.
generator — A device converting mechanical input to electrical output.
electric motor — A device converting electrical input to mechanical motion.
transformer — A device changing AC voltages through electromagnetic induction.
primary coil — The input winding of a transformer.
secondary coil — The output winding of a transformer.
alternating current — Current that reverses direction periodically.
direct current — Current that maintains a single direction.
right-hand grip rule — A rule relating current direction to magnetic field orientation.

10. Radioactivity and scientific judgement — terms 181–200

Radioactivity involves statistical randomness. The half-life describes a large population, not a countdown for the decay of one nucleus.

atomic nucleus — The compact centre of an atom containing protons and neutrons.
nucleon — A proton or neutron within a nucleus.
isotope — Atoms of one element with different neutron counts.
radioisotope — An unstable isotope that can undergo radioactive decay.
radioactivity — Spontaneous radiation emission from unstable atomic nuclei.
alpha particle — A helium nucleus emitted by some radioactive decays.
beta particle — An energetic electron or positron emitted in beta decay.
gamma radiation — High-energy electromagnetic radiation from nuclear processes.
ionising radiation — Radiation able to remove electrons from atoms or molecules.
half-life — Time for a radioactive population or activity to halve statistically.
background radiation — Ionising radiation naturally and artificially present around us.
radiation dose — A measure of energy deposited or biological effect from radiation.
contamination — Unwanted radioactive material present on or inside an object.
irradiation — Exposure to radiation without necessarily acquiring radioactive material.
count rate — Detector counts recorded per unit time.
random decay — The unpredictable timing of individual nuclear transformations.
penetrating power — Ability of radiation to pass through matter.
shielding — Using material to reduce exposure to radiation.
hazard assessment — Identifying possible harm before choosing precautions.
evidence-based conclusion — A judgement supported by observed results and valid reasoning.

Worked Physics Examples: When One Word Changes the Answer

Example 1: Distance versus displacement

A student walks 300 m east and then 300 m west along a straight path. The distance travelled is 600 m, while the final displacement is 0 m because the student returns to the starting point. If the journey takes 10 minutes (600 s), average speed is 600 ÷ 600 = 1 m/s; average velocity is 0 ÷ 600 = 0 m/s. The words are not interchangeable.

Example 2: Acceleration, units and sign

A bicycle changes velocity from 6 m/s east to 18 m/s east in 4 s. The average acceleration is (18 − 6) ÷ 4 = 3 m/s² east. A student who writes 3 m/s has calculated a rate of velocity change but has not recorded the correct unit. If the object changes direction, choose a positive direction and retain the signs.

Example 3: Work and pressure are different calculations

A force of 600 N acts normally on a flat area of 0.30 m². The pressure is 600 ÷ 0.30 = 2,000 Pa. This does not tell us how much work is done. Work requires displacement in the direction of the force; if the contact point does not move in that direction, the work done by that force may be zero despite substantial pressure.

Example 4: Power versus energy

A device transfers 900 J in 30 s. Its average power is 900 ÷ 30 = 30 W. A separate 100 W lamp run for 3 hours consumes 0.1 kW × 3 h = 0.3 kWh, which is a quantity of energy, not a rate. Students should label quantities before performing arithmetic.

Example 5: Current and potential difference

For a resistor obeying Ohm’s law under constant physical conditions, a potential difference of 12 V across resistance 4 Ω produces I = V/R = 3 A. The electrical power is P = VI = 12 × 3 = 36 W. Potential difference describes energy per unit charge, while current describes charge per unit time. They are not two names for the same thing.

Example 6: Radioactivity and half-life

Suppose a radioactive sample’s activity is initially 80 counts per second after correction for background, with a half-life of 5 days. After 10 days, which is two half-lives, the expected activity is 80 → 40 → 20 counts per second. Measurements fluctuate because decay is random. The count rate of a detector also depends on geometry and equipment efficiency, so these values are an idealised teaching example.

Example 7: Why waves require a medium—or do not

Sound travels through material media, so a sound wave cannot travel through a perfect vacuum. Light is an electromagnetic wave and can travel through a vacuum. The distinction makes practical sense in communication, space science and engineering.

Common Secondary 4 Physics Mistakes and How to Repair Them

Error: Every force causes motion. A nonzero net force causes acceleration; several forces can cancel. Sketch the object, draw the actual forces and ask whether their vector sum is zero.

Error: An energy loss means energy was destroyed. Energy is conserved, but it may be transferred to thermal stores or other less useful forms. Define the system and trace where energy goes.

Error: A fast-moving object must be accelerating. An object moving at constant speed in a straight line has zero acceleration. An object moving at constant speed around a curve changes direction and therefore has acceleration.

Error: A high current means a high voltage. The relationship depends on the circuit and resistance. A small resistance can allow a large current at a modest potential difference.

Error: An instrument with more decimal places must be more accurate. Resolution is not accuracy. A poorly calibrated device can report a very precise-looking but biased measurement.

Error: A ray refracts because the frequency changes. At a stationary boundary between optical media, frequency remains the same, while speed and wavelength change. The direction may change according to incidence conditions.

Error: Gamma rays make everything they touch radioactive. Irradiation and radioactive contamination are different ideas. Do not imply that ordinary exposure to gamma radiation leaves radioactive particles behind.

One Practical Investigation Explained in Ordinary Language

Imagine investigating how the length of a wire affects its resistance, using a suitable school laboratory setup. The independent variable is wire length. The dependent variable is calculated resistance, using voltage and current readings. Controlled factors include the wire’s material and cross-sectional area; temperature should be kept as stable as practicable because heating can alter resistance.

Take readings at several lengths, calculate resistance, plot a graph and identify the trend. Repetition may help expose random variation. A line that does not pass through the origin may have causes such as contact resistance or other systematic effects. State plausible causes and how an improved method would test them. Follow teacher instructions for electrical safety; do not improvise mains-powered experiments at home.

Physics Outside the Classroom: What These Words Help You Understand

Cooling a home: Thermal conduction, convection and radiation explain different routes by which heat enters a building. Insulation, shading and airflow address different mechanisms.

Buying appliances: The rated power of a device (watts) is not its total electricity consumption. Consumption depends on power and operating time, and actual use may differ from nominal ratings.

Transport: Braking distance depends on the motion and conditions. It is not enough to say “higher speed means more stopping distance” without considering reaction time, braking force and surface grip.

Communications: Radio, microwaves and visible light are parts of the electromagnetic spectrum; they differ in frequency and wavelength, although all are electromagnetic waves.

Four-Week Vocabulary-to-Concept Study Plan

Week 1: Learn 1–50. Define five terms from memory daily; use them to interpret a distance-time graph, velocity-time graph or free-body diagram.
Week 2: Learn 51–100. Work through pressure, moments, work, power and thermal calculations. State units at every step.
Week 3: Learn 101–150. Draw and annotate a wave diagram, a light-ray diagram and a basic circuit. Test distinctions without looking at notes.
Week 4: Learn 151–200. Explain an induction example and a radioactive-decay graph, then return to the twenty words you still confuse.

A simple progress measure is a 20-term random sample: score one point for a correct meaning and one for a relevant diagram, equation or everyday application, for 40 points possible. The value is in the error pattern, not in making revision feel like another high-stakes examination.

Frequently Asked Questions

Are these 200 terms a compulsory SEAB Physics vocabulary list?

No. This is an independent editorial glossary based on Physics concepts. Consult the year-specific official subject syllabus for examinable content, and note that some entries deepen the subject beyond a minimum requirement.

What changed from 2026 Physics 6091 to 2027 SEC Physics K323?

The subject code and examination framework change with the transition from the O-Level to the SEC G3 examination. Compare the official subject PDFs for any detailed differences; do not assume that a new code means every topic was rewritten.

Can a Combined Science student use this list?

Yes, as a reference, but the Combined Science routes have distinct subjects and codes, such as 2027 G3 K326 Science (Physics, Chemistry) and K327 Science (Physics, Biology). Not every Pure Physics term is necessarily required at the same depth.

How do I learn Physics formulas without memorising blindly?

Say what each quantity represents, write its unit and predict what should happen when one input increases. Draw a diagram and substitute units into a calculation before judging whether the answer makes sense.

Should I study definitions or worked examples first?

Use both. Read the meaning, observe a worked example, then try a slightly different example independently. A memorised definition only becomes useful when it changes your choice of method.

How can parents help with difficult Physics words?

Ask the student to explain one household example, such as why a plug needs a fuse or how a fan changes room comfort. Avoid extra worksheets until it is clear whether the problem is vocabulary, concepts or mathematical manipulation.

Official Syllabus and Further Reading

Updated 7 November 2026. This educational guide is not endorsed by MOE or SEAB; check the school candidate syllabus for the examination year actually registered.

Top 200 Vocabulary for Secondary 4 Physics | O-Level and SEC 2027 Forces, Electricity, Waves and Practical Science