Physics works by defining a physical system, measuring quantities that describe it, building a mathematical model of the interactions and constraints, using that model to make predictions, and comparing those predictions with measurements from the world.

Physics is not simply a collection of formulae. It is a disciplined way of asking how matter, energy, fields, space and time behave—and how confidently we know.

A formula is useful only when we know what system it describes, what assumptions are being made, which quantities were measured, which quantities were inferred, and where the model stops being reliable.

Physics becomes powerful when mathematics remains connected to measurement, models remain connected to their domains, and predictions remain answerable to the world.

Quick Read: The Whole Physics Map

A useful discipline-level mechanism is:

WORLD / PHYSICAL SYSTEM → BOUNDARY → OBSERVABLES → PHYSICAL QUANTITIES → UNITS & UNCERTAINTY → REPRESENTATION / MATHEMATICAL MODEL → INITIAL & BOUNDARY CONDITIONS → INTERACTIONS / FIELDS → CONSTRAINTS → DYNAMICS → CONSERVATION LAWS → PREDICTION → MEASUREMENT → RESIDUAL / UNCERTAINTY → MODEL DOMAIN → REVISION → APPLICATION → WORLD RETURN

The governing question is:

What physical system is being modelled, which quantities define its state, which interactions and constraints govern its change, which conservation laws or dynamical principles apply, what does the model predict, under what approximation is that prediction valid, and what measurement could confirm, refine or overturn it?

Reader Status and Method

Article job	Public discipline-level explanation and router for Physics
Claim status	Evidence-grounded explanatory synthesis; not a claim that Physics is complete
Method	Cross-check metrology, current Singapore curriculum, standard physics references, specialist institutional sources, worked examples and known failure modes
Evidence check	27 August 2026
Review trigger	Major change to SI/metrology standards, Singapore Physics syllabuses, or a scientific development that materially changes a statement here

This article explains the architecture of the discipline. It does not replace a Physics textbook, laboratory manual, specialist research paper, syllabus document or instrument-specific guide.

1. Physics Starts by Defining the System

Before choosing an equation, physicists decide what is inside the system and what is outside it.

The system might be a falling ball, a gas in a cylinder, an electrical circuit, an electron beam, a planet orbiting a star, a vibrating bridge, a semiconductor device or the observable universe.

That boundary determines which interactions are internal, which influences are external, which quantities can cross the boundary, and which conservation statements can be used safely.

wrong system boundary → wrong physics even when the algebra is perfect.

2. Observation Becomes a Physical Quantity Only After It Is Defined

Physics turns parts of the world into quantities that can be compared: length, time, mass, velocity, force, energy, electric current, temperature, field strength, frequency and many others.

A physical quantity is not just a number. It has meaning, a measurement procedure or operational connection, and normally a unit.

quantity ≠ numerical value ≠ unit.

3. Units Are Shared Measurement Infrastructure

The International System of Units provides a common measurement language. The BIPM identifies seven SI base quantities and units: time (second), length (metre), mass (kilogram), electric current (ampere), thermodynamic temperature (kelvin), amount of substance (mole) and luminous intensity (candela).

Since 2019, the SI has been defined through fixed numerical values of seven defining constants, including the speed of light in vacuum, Planck constant, elementary charge and Boltzmann constant. The current SI Brochure was updated in 2026.

Derived units such as newton, joule, volt and watt compress combinations of base units. Keeping dimensions and units visible is one of the simplest ways to detect impossible equations.

4. Measurement Always Carries Uncertainty

No experimental measurement is infinitely exact. Instruments have finite resolution, calibration has limits, environments fluctuate, samples vary, and measurement procedures introduce uncertainty.

NIST defines measurement uncertainty as a parameter characterising the dispersion of quantity values attributed to a measurand from the information used.

measurement uncertainty ≠ mistake.

A mistake should be corrected. Uncertainty is part of a responsible statement of what the measurement can support.

5. Precision and Accuracy Are Different

A set of repeated readings can cluster tightly and still be displaced from the best estimate of the true or reference value because of systematic effects. Conversely, measurements can scatter widely around a good central value.

precision ≠ accuracy.

This is why calibration, controls, repeated measurements and method checks matter as much as the number of decimal places displayed by an instrument.

6. Scalars and Vectors Carry Different Information

Some physical quantities are adequately described by magnitude alone. Others require direction as well.

Mass, energy and temperature are scalars. Displacement, velocity, acceleration, force and momentum are vectors.

This distinction explains why a car can move at constant speed around a curve while still accelerating: its velocity direction is changing.

7. Dimensional Reasoning Is a Physics Error Detector

An equation relating unlike dimensions cannot describe a physical equality. Dimensional analysis can therefore test homogeneity, guide scaling arguments and sometimes reveal the likely form of a relationship before detailed calculation.

It cannot determine every dimensionless numerical factor or prove that a physically possible equation is actually correct.

dimensionally consistent ≠ experimentally true.

8. Mathematics Is the Language of the Model, Not the World Itself

Physics uses equations, graphs, vectors, differential equations, probability distributions, matrices, geometry and numerical simulation because these representations compress relationships precisely.

But an equation is a representation. A graph is a representation. A field line is a representation. A wavefunction is a mathematical object in a theory.

mathematical representation ≠ literal photograph of reality.

9. Initial Conditions and Boundary Conditions Matter

The same physical laws can produce very different outcomes from different starting states.

To predict a projectile, we need its initial position and velocity. To predict heat flow, we need temperatures and boundary conditions. To solve a circuit, we need its topology, component values and sources. To predict an orbit, we need position and velocity relative to the gravitational system.

A law without the state of the system is often insufficient to determine the future.

10. Kinematics Describes Motion Before Explaining Its Cause

Kinematics describes position, displacement, velocity and acceleration as functions of time.

It answers questions such as: Where is the object? How fast is it moving? In what direction? How is its velocity changing?

speed ≠ velocity.

Speed is a scalar magnitude. Velocity contains direction. Acceleration describes change of velocity, so an object can accelerate by changing speed, direction, or both.

11. Dynamics Connects Interactions to Changes in Motion

Newtonian mechanics provides an extraordinarily successful model for a wide range of everyday and engineering systems.

Newton’s first law separates motion from the need for a continuing net force: in an inertial frame, zero net external force means constant velocity, not necessarily rest.

Newton’s second law connects net external force to the rate of change of momentum; for constant mass in ordinary introductory situations this becomes the familiar F = ma.

force ≠ motion; net force → change in momentum.

12. Mass and Weight Are Not the Same Quantity

Mass characterises inertia and contributes to gravitational interaction. Weight is a force associated with gravity in the relevant context.

An astronaut does not lose mass merely because apparent weight changes in orbit.

mass ≠ weight.

13. Momentum Tracks Motion in Interacting Systems

Linear momentum combines mass and velocity. Impulse connects force acting over time to change in momentum.

For a suitably isolated system, total momentum is conserved even during a violent collision whose internal forces are large and rapidly changing.

That does not mean kinetic energy must also be conserved. In an inelastic collision, some kinetic energy can be transferred into internal energy, deformation, sound and other stores while total momentum remains conserved.

momentum conservation ≠ kinetic-energy conservation.

14. Energy Is a Powerful Accounting Quantity

Energy lets physicists connect states without following every microscopic detail of the path between them.

Systems can store energy in kinetic, gravitational, elastic, thermal, chemical, electrical and other forms depending on the model. Energy can be transferred by work, heating, radiation and matter flows.

Conservation of energy does not mean every process is reversible or that all energy remains equally useful. The form and distribution of energy matter.

15. Power Is the Rate of Energy Transfer

Two machines can transfer the same amount of energy but do so over different times. Power distinguishes them.

energy ≠ power.

A high-power device transfers energy rapidly. A high-energy store may contain a large amount of transferable energy without delivering it quickly.

16. Rotation Adds Torque and Angular Momentum

Extended objects can translate and rotate. Rotational mechanics introduces angular displacement, angular velocity, moment of inertia, torque and angular momentum.

Mass distribution matters: two objects with the same total mass can respond differently to the same torque because their mass is distributed differently relative to the axis.

17. Gravitation Connects Falling Objects, Orbits and Cosmic Structure

Newtonian gravitation explains an enormous range of planetary and satellite motion. An orbit is not an absence of gravity; it is continuous free fall around a curved path.

At stronger gravitational fields, high precision or relativistic conditions, general relativity provides the deeper framework.

For a specialist example, see eduKate Learning Manual: Lagrange Points.

18. Oscillations Reveal Restoring Forces, Energy Exchange and Stability

Many systems displaced from stable equilibrium experience a restoring influence. Springs, pendulums, electrical resonators, molecules and structures can oscillate.

Simple harmonic motion is an ideal model in which acceleration is proportional to displacement and directed toward equilibrium. Real oscillators may also include damping, nonlinear response and external driving.

19. Waves Transfer Energy and Information Without Requiring Bulk Matter to Travel With the Pattern

A wave is a propagating disturbance described by quantities such as amplitude, wavelength, frequency, phase and wave speed.

The particles of a medium can oscillate locally while the wave pattern travels much farther.

wave propagation ≠ bulk transport of the medium.

Frequency is set by the oscillation rate of the source in ordinary wave situations, while wave speed depends on the medium and physical conditions. Wavelength adjusts through the relationship among speed, frequency and wavelength.

frequency ≠ wave speed.

20. Superposition Creates Interference, Diffraction and Standing Patterns

When a system is sufficiently linear, overlapping waves add according to superposition. Their phases determine whether the resulting displacement is enhanced, reduced or reorganised into a standing pattern.

Diffraction reveals that wave behaviour becomes especially important when obstacles or apertures are comparable with wavelength.

21. Resonance Is Large Response Near a System’s Natural Dynamics

A driven oscillator can respond strongly when the driving frequency lies near a natural frequency, with the exact response shaped by damping and coupling.

Resonance can be useful in radios, sensors and spectroscopy, or dangerous in structures and machines if energy accumulates faster than it is dissipated.

22. Temperature and Heat Are Different Physical Ideas

Temperature characterises thermal state. Heat is energy transferred because of a temperature difference.

heat ≠ temperature.

A small hot object can have a higher temperature than a large cooler object while containing less total internal energy.

For a specialist mechanism, see eduKate Learning Manual: Heat Conduction.

23. Statistical Physics Connects Microscopic Motion to Macroscopic Behaviour

A gas contains an enormous number of particles. Tracking every particle individually is usually impossible and unnecessary.

Statistical mechanics connects distributions of microscopic states to macroscopic quantities such as pressure, temperature and entropy. The ideal-gas model is powerful precisely because it deliberately ignores many complications while preserving the relationships needed for a useful domain.

24. Thermodynamics Constrains Which Macroscopic Changes Are Possible

The first law is an energy-accounting statement for thermodynamic systems. The second law introduces directionality and entropy, explaining why many processes occur readily in one macroscopic direction but not spontaneously in reverse.

Energy conservation alone cannot tell us whether a proposed process is physically achievable with the claimed direction and efficiency.

25. Electric Charge Creates Electric Interaction

Electric phenomena arise from charge and electromagnetic interaction. Charge can be positive or negative, and total charge is conserved in ordinary processes.

An electric field describes how the environment around charges is structured so that another charge placed there may experience force.

field ≠ force on every object.

A neutral test object and a charged test object can respond differently even at the same location.

26. Electric Field and Electric Potential Are Related but Different

Electric field is a vector quantity connected to force per unit charge. Electric potential is a scalar quantity connected to potential energy per unit charge.

The field is related to how potential changes with position, but the two quantities are not interchangeable.

electric potential ≠ electric field.

27. Current, Potential Difference and Electrical Energy Must Stay Separate

Electric current measures rate of charge flow. Potential difference measures energy transfer per unit charge between points. Resistance describes a relationship between potential difference and current for a component under stated conditions.

current ≠ voltage ≠ electrical energy.

A circuit diagram is therefore a model of connectivity and component behaviour, not a picture of electrons being consumed as they travel around the loop.

28. Capacitors Store Energy in an Electric Configuration

A capacitor stores separated charge and energy associated with its electric field. Capacitance connects stored charge to potential difference for a defined geometry and material configuration.

Charging and discharging through resistance introduce characteristic time behaviour. This is a useful example of Physics connecting a component model, differential change, energy storage and measurement on one system.

29. Magnetism and Moving Charge Are Part of Electromagnetism

Magnetic fields interact with moving charges, currents and magnetic moments. Currents generate magnetic fields, and changing magnetic flux can induce electromotive effects.

Electromagnetic induction connects generators, transformers, motors, wireless systems and much of modern electrical infrastructure.

For a specialist measurement route, see eduKate Learning Manual: The Hall Effect.

30. Light Is Electromagnetic Radiation—and Its Behaviour Depends on the Experiment

Geometric optics models light with rays and is extremely effective when wavelengths are small relative to the structures involved. Wave optics explains interference, diffraction and polarisation. Quantum physics is required when energy exchange in discrete photons becomes central.

ray model ≠ complete theory of light.

Different models can be valid at different resolutions without one being useless merely because a deeper model exists.

31. Relativity Changes the Model When Speed, Gravity or Precision Demands It

Special relativity changes how space and time are related when relative speeds become significant compared with the speed of light. General relativity describes gravitation through spacetime geometry rather than Newtonian force alone.

This does not make Newtonian mechanics “wrong” for everyday engineering. It identifies the domain in which Newtonian mechanics is an excellent approximation.

relativity ≠ “everything is relative”.

For a specialist observational example, see eduKate Learning Manual: Gravitational Lensing.

32. Quantum Physics Changes What Counts as a Physical State and Prediction

At atomic and subatomic scales, classical pictures fail. Quantum theory describes states using mathematical structures whose predictions are often probabilistic for measurement outcomes.

Particles such as electrons can produce diffraction and interference patterns under appropriate experimental conditions. OpenStax summarises matter-wave behaviour as experimentally observable, and electron diffraction is one of the classic routes by which classical particle-only pictures fail.

quantum state ≠ tiny classical object secretly following an ordinary trajectory described by the diagram.

Explore the specialist route in eduKate Learning Manual: Electron Diffraction and The Stern–Gerlach Experiment.

33. Atomic Physics Connects Quantised States to Spectra

Atoms have quantised energy structures. Transitions among allowed states can absorb or emit radiation with characteristic energies.

Spectra therefore become evidence about internal atomic structure, but the interpretation depends on the quantum model, experimental resolution and environment.

See The Franck–Hertz Experiment and The Zeeman Effect.

34. Nuclear Physics Separates Nuclear Structure From Atomic Electron Structure

The nucleus contains protons and neutrons bound through nuclear interactions, while atomic chemistry is dominated by electrons and electromagnetic interaction.

Radioactive decay is probabilistic for individual unstable nuclei but statistically predictable for large populations. Nuclear fission and fusion involve changes in nuclear binding and can release large energies because nuclear energy scales are much larger than ordinary chemical bond energies.

nuclear reaction ≠ chemical reaction.

35. Particle Physics Searches for More Fundamental Building Blocks and Interactions

CERN describes the Standard Model as our best-tested framework for the elementary particles and three of the four fundamental interactions, while gravitation is not incorporated into that model.

Quarks and leptons are fundamental matter particles in the Standard Model. Gauge bosons mediate interactions, and the Higgs field is associated with the Higgs boson and the mechanism by which elementary particles acquire mass within the theory.

The Standard Model is extraordinarily successful but not a complete theory of everything. That incompleteness is part of modern Physics, not an embarrassment to hide.

36. Cosmology Applies Physics to the Largest Observable System

Cosmology studies the origin, structure and evolution of the universe using general relativity, particle physics, thermodynamics, nuclear physics, astronomy and statistical inference.

Observations support an expanding universe and indicate large gravitational effects attributed to dark matter as well as accelerated expansion associated with what is called dark energy. The physical nature of both remains an active research problem.

name for an inferred phenomenon ≠ complete explanation of its physical nature.

For specialist routes, see The Hubble–Lemaître Law and Gravitational Lensing.

37. Conservation Laws Are Among Physics’ Strongest Compression Tools

Conservation of energy, momentum, angular momentum and electric charge allow physicists to rule out impossible outcomes without calculating every microscopic detail.

At deeper theoretical levels, symmetries and conservation laws are closely connected. But the practical lesson is simple: first identify the system and whether the relevant symmetry or isolation condition applies.

conservation law without a correctly defined system can become a bookkeeping error.

38. Approximation Is a Strength When Its Domain Is Visible

Physics constantly simplifies:

• point masses;
• rigid bodies;
• frictionless surfaces;
• massless strings;
• ideal gases;
• uniform fields;
• small-angle approximations;
• linear response;
• negligible air resistance;
• isolated systems.

These are not claims that the real world literally contains perfect point masses or frictionless surfaces. They are controlled simplifications.

approximation ≠ carelessness; hidden approximation = danger.

39. Model Domain Is as Important as Model Accuracy

A model can be extremely accurate in one domain and fail badly outside it.

Newtonian mechanics works beautifully for most everyday motion but requires relativistic correction at sufficiently high speeds or precision. Geometric optics works when wavelength effects are negligible but fails to explain interference. Classical particle trajectories fail to capture quantum interference.

The revised Singapore H2 Physics syllabus makes this point explicitly: older paradigms such as Newtonian mechanics remain relevant because coherent use of their principles gives excellent agreement between theory and experiment in many cases.

40. Residuals Tell Us Where the Model and World Disagree

After a model predicts an observable quantity, physicists compare prediction with measurement.

The difference can arise from:

• measurement uncertainty;
• calibration error;
• incorrect initial conditions;
• missing variables;
• an approximation used outside its range;
• incorrect parameter values;
• statistical fluctuation;
• a genuinely inadequate model.

A residual is therefore not automatically “new physics”. It is a prompt to test the entire evidence chain.

41. Prediction and Explanation Are Related but Not Identical

A model may predict data accurately without settling every question about what its mathematical objects mean physically. Different models can also make nearly identical predictions within a limited experimental range.

This is why stronger experiments are designed to discriminate among alternatives rather than merely confirming one expected result.

successful prediction ≠ proof that every part of the model is literally true.

42. Computation Extends Physics Beyond Analytically Solvable Problems

Many realistic systems cannot be solved exactly with a neat closed-form equation. Numerical integration, simulation, optimisation and statistical computation allow physicists to study complex fluids, climate processes, materials, plasmas, gravitational systems and quantum models.

But computation does not remove the need for physical reasoning. A simulation inherits its equations, approximations, boundary conditions, numerical methods and input data.

more computation ≠ more truth unless the model and evidence chain are sound.

43. Instruments Translate Physical Interaction Into Data

A detector rarely measures the final scientific claim directly. It responds to some physical interaction and produces a signal.

The evidence chain is:

physical event → interaction with detector → transduction → raw signal → calibration → processing → derived quantity → physical inference.

Every arrow can introduce uncertainty or bias. Instrument precision cannot rescue a detector that is measuring the wrong physical quantity.

44. Reproducibility and Independent Measurement Strengthen Physical Claims

A single striking result can be important, but Physics becomes more reliable when measurements can be checked, methods can be reconstructed, instruments can be independently calibrated and alternative explanations can be tested.

Agreement across different methods is especially powerful because different instruments often carry different failure modes.

Worked Example 1: A Thrown Ball and the Hidden Assumptions

Suppose a ball is thrown through the air.

A simple school model may treat the ball as a point mass, use constant gravitational acceleration, neglect air resistance and assume a flat local Earth.

The chain is:

initial position + initial velocity → gravitational acceleration → horizontal and vertical motion → predicted trajectory → measured landing point.

If the measured trajectory disagrees, the first response should not be “Newton’s laws failed”. Check air drag, wind, spin, launch conditions, measurement error and whether the constant-gravity approximation is adequate.

The model is useful precisely because its assumptions are visible.

Worked Example 2: A Collision Separates Momentum From Kinetic Energy

Imagine two carts collide on a nearly frictionless track and stick together.

For the two-cart system, external impulse during the short collision may be negligible, so total momentum before and after is approximately conserved.

But because the carts stick, kinetic energy decreases. The “missing” kinetic energy has not vanished; it has been transferred into deformation, internal energy, sound and other forms.

same event → momentum accounting and energy accounting answer different questions.

Worked Example 3: A Simple Electrical Circuit

Connect a cell and resistor in a closed circuit.

A useful chain is:

source establishes potential difference → electric field is established through the circuit → charge carriers respond → current flows → electrical energy is transferred → resistor’s internal energy increases → energy leaves to surroundings.

The current is not “used up” by the resistor. Charge is conserved. What is transferred and dissipated is energy.

charge flow continues around the circuit; energy transfer changes form.

Worked Example 4: Electron Diffraction Breaks the Classical Particle-Only Picture

Send electrons toward a crystal or suitable diffraction geometry.

A purely classical picture of tiny particles following definite ordinary trajectories does not predict the observed diffraction structure. Quantum theory associates matter-wave behaviour with electrons and predicts interference and diffraction under appropriate conditions.

The important lesson is not merely “electrons are waves”. It is that the experimental arrangement determines which aspects of the quantum system become observable, and classical categories alone are insufficient.

Hostile Test: The Model Predicts the Data, Therefore the Model Must Be Literally True

Suppose a model predicts every measurement made so far within experimental uncertainty. Have we proved that every object and mathematical structure inside the model literally exists exactly as pictured?

No.

Several models can sometimes reproduce the same observations inside a restricted domain. Some models are effective approximations of deeper theories. Some mathematical objects are representations whose interpretation remains debated even while predictions are excellent.

The correct scientific response is:

prediction matches measurement → model survives this test → identify alternatives → design discriminating measurements → expand the tested domain → revise when required.

Where Physics Explanations Commonly Break

Failure	What goes wrong	Repair question
System blindness	The boundary is never defined	What exactly is inside the system?
Quantity-unit collapse	A unit is treated as the physical quantity	What is being measured, and in which unit?
Precision-accuracy collapse	More decimal places are assumed to mean more truth	What systematic effects and calibration limits remain?
Uncertainty-as-error	Legitimate uncertainty is treated as a mistake	What range of values is supported by the measurement process?
Formula hunting	An equation is chosen before the model	Which physical law and assumptions justify this equation?
Force-motion collapse	Motion is assumed to require continuing net force	Is velocity changing?
Mass-weight collapse	Mass and gravitational force are interchanged	Which quantity is being described?
Momentum-energy collapse	Both are assumed conserved in every collision	Which conservation conditions actually apply?
Energy-power collapse	Amount transferred becomes rate of transfer	How much energy, over what time?
Heat-temperature collapse	Thermal state and energy transfer are confused	Is this temperature, internal energy or heat transfer?
Field-force collapse	A field is treated as the force itself	What test object or charge couples to the field?
Voltage-current collapse	Potential difference and charge-flow rate are treated as one quantity	What is driving, and what is flowing?
Wave-medium collapse	The wave is treated as bulk material travelling with the pattern	What oscillates locally and what propagates?
Frequency-speed collapse	Oscillation rate is confused with propagation speed	Which property belongs to the source and which to the medium?
Model absolutism	A successful approximation becomes universal	What is the model’s tested domain?
Residual sensationalism	Any mismatch becomes “new physics”	Have uncertainty, calibration and missing variables been eliminated?
Simulation certainty	Numerical output is treated as observation	Which equations and assumptions generated it?
Quantum-classical collapse	Quantum objects are forced into ordinary hidden trajectories	What does the theory actually predict for the measurement?
Relativity slogan	Relativity becomes “everything is relative”	Which invariants and reference-frame relations does the theory specify?
Cosmic label-as-cause	Dark matter or dark energy is treated as a completed mechanism	What is observed, what is inferred, and what remains unknown?

How to Read Any Physics Story

1. System: What physical object or region is being studied?
2. Boundary: What is inside and outside the system?
3. State: Which quantities describe it now?
4. Units: Are the quantities defined consistently?
5. Measurement: Which quantities are directly measured?
6. Uncertainty: What limits the measurement?
7. Representation: Which diagram, graph or mathematical model is being used?
8. Initial conditions: What starting information is required?
9. Interactions: Which forces, fields or couplings matter?
10. Constraints: What is fixed or forbidden?
11. Dynamics: Which law governs change?
12. Conservation: Which quantities remain constant for the chosen system?
13. Prediction: What observable result follows?
14. Domain: Under what approximation is the model valid?
15. Residual: How far is prediction from measurement?
16. Alternatives: What other explanation fits?
17. World return: What new measurement could strengthen, weaken or overturn the model?

Current Evidence and Standards Anchors

No single source owns all of Physics. Useful high-authority starting points include:

• BIPM — International System of Units for the SI measurement framework and defining constants.
• BIPM — SI Brochure, ninth edition, updated in 2026.
• NIST — Measurement Uncertainty for the measurement evidence chain.
• NIST / CODATA Fundamental Physical Constants for evaluated constants and uncertainties.
• CERN — The Standard Model for the current particle-physics framework and its limits.
• NASA Physics of the Cosmos for large-scale tests of gravitation, extreme matter and cosmology.
• OpenStax University Physics for an openly accessible calculus-based reference across mechanics, waves, thermodynamics, electromagnetism and modern physics.

Version boundary: physical constants, evaluated uncertainties, instrument calibrations, educational syllabuses and scientific interpretations can be updated. Keep edition, method, date and uncertainty attached where they materially affect a claim.

Singapore Learning Boundary: Physics Is Larger Than the Examination Syllabus

Singapore school Physics samples part of the much larger discipline described above.

As at 27 August 2026, SEAB’s 2026 A-Level list contains both revised H2 Physics 9478 and legacy H2 Physics 9749, with 9749 explicitly marked as its last year of examination in 2026. SEAB also lists 9478 for the 2027 examination year. This transition matters: a student should use the syllabus code attached to the examination route actually being taken.

The revised 9478 syllabus describes Physics as creating useful models of the universe from a small number of basic principles, working out their implications and comparing them against observations. It explicitly notes that older paradigms such as Newtonian mechanics remain relevant where they continue to agree well with experiment.

The 9478 content is organised into Foundations of Physics, Mechanics, Waves, Thermal Physics, Electricity and Magnetism, and Modern Physics. Measurement and uncertainty anchor the foundation. Its practical assessment also keeps planning, measurement, data handling, analysis and evaluation inside the discipline rather than treating laboratory work as an optional extra.

For learning mechanisms, see How Secondary Science Works and How JC Science Works. The overarching knowledge-building owner remains How Science Works.

Where Physics Meets Chemistry, Biology and Medicine

Physics provides deep foundations for atomic structure, spectroscopy, thermodynamics, fluid flow, electrical signalling, imaging and radiation. But neighbouring disciplines ask different organising questions.

• How Chemistry Works owns chemical species, structure, bonding, reactions, mixtures and chemical measurement.
• How Biology Works owns organised living systems, regulation, reproduction, inheritance, evolution and ecology.
• How Medicine Works owns patient state, clinical evidence, benefits, harms, consent, care and human outcomes.

physical mechanism can constrain chemistry, biology and medicine without replacing their higher-level organising questions.

Where This Fits in the eduKate World Map

This is the public discipline-level front door for Physics. It owns the physics engine and routes specialist questions rather than duplicating every existing leaf article.

• How Science Works owns scientific knowledge-building, evidence and correction.
• How Physics Works owns the discipline-level physical-system mechanism.
• Physical World Science and eduKate Learning Manuals retain specialist mechanisms, experiments and phenomena.
• Laboratory Practices retains experimental execution, safety, records, calibration and reproducibility.
• How Chemistry Works owns chemical structure and transformation.
• How Biology Works owns living organisation.
• How Medicine Works owns clinical decisions and human care.

What This Article Does Not Prove

• It does not prove that current Physics is complete.
• It does not claim that one interpretation of quantum mechanics has been established by this overview.
• It does not identify the physical nature of dark matter or dark energy.
• It does not make the Standard Model a theory of gravitation.
• It does not make every classical approximation valid outside its tested domain.
• It does not turn a simulation into an observation.
• It does not turn agreement with existing data into proof that no alternative model can fit.

Observable Mastery Test

Choose one physical system: a falling ball, bicycle braking, a collision, a pendulum, a loudspeaker, a kettle, an electrical circuit, a solar panel, an electron-diffraction experiment or a satellite orbit.

You understand how Physics works if you can trace:

system → boundary → observable quantities → units → measurement uncertainty → representation → initial conditions → interactions / fields → constraints → dynamics → conservation → prediction → measurement → residual → model domain → revision → world return.

Then ask four correction questions:

• Which part of the explanation was directly measured?
• Which part was inferred through a model?
• Which assumption makes the calculation possible?
• What observation would make the model weaker?

If the physical story cannot change when careful measurement disagrees with it, it is no longer functioning as scientific Physics.

Physics is not understood when we can substitute numbers into a formula. It is understood when we can define the system, measure the world, justify the model, predict what should happen, state the approximation, and return to observation to see whether nature agrees.