What is Physics? The Study of How Things Work

Why does a ball fall when you let it go? Why is the sky blue? How does a phone know where you are? How can an invisible force hold the Moon in orbit? Physics is the science that tries to answer questions like these, from the smallest particles inside an atom to the largest structures in the universe. The word comes from the Greek physis, meaning nature. Physicists look for the simple rules that lie behind the complicated things we see, test those rules with careful experiments, and write them in the language of mathematics. This opening article explains what physics is, how scientists work, how we measure things, and how to read graphs and handle numbers. It also serves as a map to the rest of the EDUSAMBAM physics series.

1.What Physics Is

Physics is the study of matter, energy, and the forces and interactions between them. It asks what things are made of, how they move, how energy is stored and transferred, and what rules govern everything from falling apples to galaxies. Because physics looks for basic principles, it underlies other sciences. Chemistry depends on the physics of atoms and electrons; biology on the physics of molecules, fluids and electrical signals; geology on heat flow and forces inside the Earth; and engineering on all of them.

Physics has three characteristic features:

• It relies on measurement and evidence. A claim is accepted only if experiments and observations support it.
• It uses mathematics. Equations such as v = fλ or F = ma let us make exact predictions.
• It seeks unity. Newton showed that one law of gravity explains both a falling apple and the Moon's orbit. Maxwell showed that electricity, magnetism and light are linked. Physicists keep searching for deeper connections.

2.Why Study Physics?

Physics is not only for scientists. It explains the technology around you and builds skills that every career needs: logical thinking, careful measurement and problem solving.

• Technology: the electric motors and generators in the electricity article, the optical fibres in the light article, the satellites in the gravity article, and the transistors and lasers inside computers and phones all come from physics. The clocks on GPS satellites even need corrections from Einstein's theories of relativity, amounting to tens of microseconds per day, or navigation would drift by kilometres.
• Medicine: X-ray and ultrasound imaging, MRI scanners (which use strong magnetic fields), radiotherapy for cancer, pacemakers and laser surgery.
• Energy and environment: designing efficient engines, solar panels, wind turbines and batteries, and understanding the climate system.
• Everyday choices: why seat belts save lives, how to keep a home warm cheaply, why you should not use a phone charger in the bath, and how to judge claims about "miracle" products.
• Careers: engineering of every kind, medicine and medical physics, aviation, meteorology, data science and computing, architecture, space science, teaching and research.

3.The Branches of Physics

4.A Short History of Physics

Physics is a human story that spans many cultures and centuries. Here are a few landmarks.

Notice that discoveries build on each other: Faraday's experiments helped Maxwell, Maxwell's equations led to relativity, and so on. Scientists everywhere, from every culture, contribute to this shared body of knowledge.

5.How Scientists Work

There is no single fixed recipe, but most scientific investigations follow a cycle like the one below.

• A hypothesis is a testable, proposed explanation. A good one makes a prediction that experiments could prove wrong (it is falsifiable).
• A fair test changes only one factor at a time. The independent variable is what you deliberately change; the dependent variable is what you measure; the control variables are everything else, which you keep the same.
• Results are analysed with calculations and graphs, then compared with the prediction. A hypothesis that survives many tests may become part of a theory: a well-tested explanation that links many observations. This is a stronger meaning than the everyday phrase "just a theory".
• Scientists publish their methods and results so others can check and replicate them. Independent peer review by experts helps catch errors. Science also changes: new evidence can refine or replace earlier ideas, as relativity refined Newton's gravity for extreme conditions.

6.Measurement and SI Units

A measurement has two parts: a number and a unit. "5" means nothing; "5 m" or "5 s" does. To share results across the world, scientists use the International System of Units (SI). It has seven base units:

Since 2019 all seven units have been defined using fixed values of fundamental constants of nature. Before then the kilogram was the mass of a platinum-iridium cylinder kept near Paris; now, nothing physical needs to be kept. Other quantities have derived units built from the base units:

To avoid very long numbers, we use prefixes that multiply units by powers of ten:

Standard form writes a number as A × 10ⁿ, where 1 ≤ A < 10. For example, the speed of light is 3.00 × 10⁸ m/s and the mass of an electron is about 9.11 × 10⁻³¹ kg.

An important tool is dimensional checking. Both sides of an equation must have the same units. For example, in v = fλ, hertz × metres = (1/s) × m = m/s, which is the unit of speed ✓. If the units do not match, the equation (or your algebra) is wrong.

Scalars and vectors. A scalar has size only (mass, time, speed, energy); a vector has size and direction (displacement, velocity, force, acceleration). Two forces of 3 N and 4 N acting at right angles do not give 7 N but 5 N, found with Pythagoras' theorem, because direction matters.

7.Scale: From Protons to the Universe

Physics covers an astonishing range of sizes, more than 40 orders of magnitude. An order of magnitude is a factor of ten. Using powers of ten helps us estimate and compare.

8.Measuring Instruments

• Read at eye level and look straight on to avoid parallax error. For a measuring cylinder, read the bottom of the meniscus (the curved surface).
• Check for zero error before starting. If an instrument reads a non-zero value when it should read zero, subtract that error (or add it, if the error is negative) from every reading.
• To measure a small quantity accurately, measure many together and divide: the thickness of one sheet of paper from a stack of 200 sheets, or the period of a pendulum from 20 swings.

9.Accuracy, Precision and Error

No measurement is perfect. Two ideas describe how good it is:

• Accuracy: how close a measurement is to the true value.
• Precision: how close repeated measurements are to each other.

• Random errors vary unpredictably from one reading to the next (for example, human timing). They make results scatter, and are reduced by repeating and averaging.
• Systematic errors push every reading the same way (a zero error, a stopwatch that runs fast, a wrongly calibrated scale). Repeating does not remove them; you must find and correct the cause.

Significant figures. Your final answer should not suggest more accuracy than the data justify. For multiplication and division, give the answer to the same number of significant figures as the least precise value used. For example, 5.0 × 3.21 = 16.05, which is quoted as 16 (2 significant figures). Do not round intermediate steps; round only at the end.

10.Graphs and Relationships

Graphs reveal the relationship between two quantities. Plot the independent variable on the horizontal axis, label axes with quantity and unit, choose a scale that uses most of the paper, mark each point clearly, and draw a smooth line of best fit (it need not pass through every point but should have roughly equal points on either side).

For a straight-line graph y = mx + c, the gradient m = (change in y) ÷ (change in x) and the intercept c is where the line crosses the y-axis. Gradients often have a physical meaning: on a distance–time graph the gradient is speed, on a velocity–time graph it is acceleration, on a force–extension graph it is the spring constant.

11.How to Solve Physics Problems

1. Read the question twice and draw a labelled diagram.
2. List what is given (with units) and what you need to find.
3. Choose the equation that links them, and rearrange it before substituting numbers.
4. Convert all quantities to SI units.
5. Substitute the values, with units, and calculate.
6. Check the answer: does it have the right unit, an appropriate number of significant figures, and a sensible size? (Is a car's speed 3 × 10⁸ m/s? Surely not.)

Learn to understand, not just memorise: ask "why does this make sense?" for each formula. Use real-life examples, practise many problems of different types, and learn from errors rather than hiding them.

12.Open Questions in Physics

Physics is not finished. Some of the biggest open questions are:

• What are dark matter and dark energy? Observations of galaxies and the expansion of the universe suggest that most of the universe is made of things we cannot yet identify.
• How do gravity and quantum mechanics fit together? Each works superbly in its own domain, but we do not yet have a complete, tested theory that combines them.
• Can we make nuclear fusion work as a clean source of energy? It powers the Sun, but controlling it on Earth is a major engineering challenge.
• What happens inside black holes, and how did the universe begin?
• Quantum technologies, such as quantum computers and sensors, are being developed and are an active area of research.

The next great discoveries might come from someone who is learning the basics today.

13.Common Mistakes to Avoid

14.Check Your Understanding

Try each question before opening the answer.

Summary

• Physics studies matter, energy, forces and their interactions, using evidence, mathematics and a drive for unified explanations.
• Its branches include mechanics, thermal physics, waves and optics, electricity and magnetism, atomic and nuclear physics, astronomy and modern physics.
• Scientists work in a cycle of observation, hypothesis, prediction, experiment, analysis and sharing, using fair tests and peer review.
• Measurements have a number and an SI unit; use prefixes, standard form, and careful reading of instruments.
• Accuracy is closeness to the true value; precision is closeness of repeated readings. Random errors are reduced by repeating; systematic errors must be corrected.
• Graphs show relationships; gradients and intercepts carry physical meaning.

Explore the EDUSAMBAM Physics Series

Sources and Further Reading

This article is original EDUSAMBAM writing. Definitions, constants and historical facts were checked against the sources below. Diagrams are original and were not copied from any source.

• BIPM: the SI Brochure and the 2019 redefinition of the SI base units. BIPM — The International System of Units.
• NIST: SI units, prefixes and fundamental physical constants. NIST — SI Units; NIST — Fundamental Physical Constants.
• OpenStax, University Physics Volume 1: units, measurement, uncertainty and vectors. OpenStax — University Physics Volume 1.
• Encyclopaedia Britannica: Physics; Ibn al-Haytham; al-Biruni.
• Nobel Prize: Abdus Salam, Physics 1979. NobelPrize.org — Abdus Salam.
• CERN (Higgs boson, 2012): home.cern. LIGO (gravitational waves, 2015): ligo.caltech.edu.
• Further reading kept from the original article: Physics — CERN.
• Further reading kept from the original article: Learn Science with NASA.

Note on the numbers: historical dates are the commonly accepted ones; for some early scientists they are approximate. Please check numerical values against your own syllabus or exam board specification before relying on them.