Science explained, one question at a time
Evergreen explanations across scientific reasoning, physics, chemistry, Earth and life science, astronomy and technology.
What science is—and what it is not
Science is a way of building and testing explanations about the natural world using observation, measurement, models and evidence.
Science guideHypothesis, theory and law: the differences
In science, a hypothesis, theory and law are different kinds of statements; a theory does not simply 'graduate' into a law.
Science guideWhy science uses standard units
Standard units let measurements be communicated, compared and reproduced without ambiguity.
Science guideAccuracy, precision and measurement uncertainty
A measurement can be repeatable without being close to the true value, and every real measurement has some uncertainty.
Science guideWhy scientists use models
Models simplify reality so scientists can reason about systems that are too large, small, slow, fast or complicated to study directly in every detail.
Science guideCorrelation and causation are not the same thing
Two things can change together without one causing the other.
Science guidePeer review, replication and scientific confidence
Peer review checks whether research is suitable for publication, while replication and later evidence show whether a result is dependable.
Science guideHow to evaluate a science claim
A strong science claim tells you what was measured, how it was measured, what comparison was made and how large the uncertainty is.
Science guideMotion, speed and acceleration
Motion is described relative to a reference point, while speed and acceleration describe how position and velocity change over time.
Science guideForces and Newton's laws in everyday motion
Forces change motion, and Newton's laws provide a compact framework for understanding pushes, pulls and acceleration.
Science guideGravity from falling objects to orbits
Gravity attracts masses and shapes motion from a dropped object to the orbit of the Moon.
Science guideHow friction makes motion possible—and resists it
Friction opposes relative sliding, yet walking, driving and gripping objects depend on it.
Science guidePressure in air and liquids
Pressure is force distributed over area, and it helps explain atmospheric effects, hydraulics and why fluids push in all directions.
Science guideEnergy: forms, storage and transfer
Energy is a conserved quantity that can be stored and transferred in many ways.
Science guideConduction, convection and radiation
Heat transfer occurs through particle interactions, fluid motion and electromagnetic radiation.
Science guideHow insulation slows heat transfer
Insulation works by reducing the rate at which thermal energy moves through a material or assembly.
Science guideHow sound waves work
Sound is a mechanical disturbance that travels through matter as variations in pressure and particle motion.
Science guideLight and the electromagnetic spectrum
Visible light is only a narrow portion of the electromagnetic spectrum, which also includes radio waves, infrared, ultraviolet, X-rays and gamma rays.
Science guideReflection and refraction
Light can bounce from surfaces, change direction when entering a new material and split into colours because wavelength matters.
Science guideWhy the daytime sky looks blue
The sky looks blue mainly because molecules in the atmosphere scatter shorter visible wavelengths more strongly than longer ones.
Science guideHow rainbows form
Rainbows appear when sunlight is refracted, reflected and dispersed inside many water droplets.
Science guideColour: light, pigments and perception
Colour depends on the spectrum reaching the eye, how materials absorb or reflect wavelengths, and how the visual system interprets the signal.
Science guideLenses, magnification and cameras
Curved lenses redirect light to form images, allowing eyes, cameras, microscopes and telescopes to focus or magnify details.
Science guideElectricity and basic circuits
Electric circuits provide paths for charge to move and transfer energy through components.
Science guideMagnetism and electromagnets
Magnetic fields arise from moving electric charges and magnetic properties of matter.
Science guideHow batteries store and deliver energy
A battery uses chemical reactions to create an electrical potential difference between its terminals.
Science guideAtoms, molecules and chemical bonds
Matter is built from atoms, and chemical bonds hold atoms together in molecules and extended structures.
Science guideHow the periodic table organizes elements
The periodic table arranges elements by atomic number so repeating chemical patterns line up in groups.
Science guideWhat happens in a chemical reaction
Chemical reactions rearrange atoms by breaking and forming bonds while conserving the number of each kind of atom.
Science guideAcids, bases and pH
Acid-base chemistry describes proton transfer and related changes in aqueous solutions.
Science guideWhy water has unusual properties
Water's molecular shape and hydrogen bonding help explain its high heat capacity, surface tension and unusual behaviour when freezing.
Science guideWhy water expands when it freezes
Most materials contract as they cool, but ordinary ice forms a crystal structure that is less dense than liquid water.
Science guideSurface tension, droplets and soap bubbles
Surface tension comes from cohesive molecular forces at a liquid surface.
Science guideHow soap and detergents work
Surfactants have molecular regions that interact differently with water and oily substances, helping detach and disperse soils.
Science guideHow adhesives stick
Adhesives work through a combination of surface wetting, molecular attraction, mechanical interlocking and internal strength.
Science guideWhy glass is transparent—and why it can break
Ordinary glass is an amorphous solid whose electronic structure allows much visible light to pass through while its brittle structure limits how it handles cracks.
Science guidePolymers and plastics
Polymers are long-chain molecules whose composition and structure create a wide range of flexible, rigid, clear, tough or heat-resistant materials.
Science guideThe science of textile fibres
Fabric behaviour comes from fibre chemistry, yarn structure, weave or knit construction and finishing treatments.
Science guideFragrance, volatile molecules and smell
Smell begins when volatile molecules reach olfactory receptors in the nose and trigger patterns of neural signals.
Science guideThe science of fermentation
Fermentation uses microbial metabolism to transform sugars and other compounds into products such as acids, gases or alcohols.
Science guideHow heat transforms food
Cooking changes food through heat transfer, water movement, protein changes, starch behaviour and chemical reactions.
Science guideWhat the Maillard reaction is
The Maillard reaction is a family of heat-driven reactions involving amino compounds and reducing sugars that produce many browned-food aromas, flavours and pigments.
Science guideWhy oil and water can form emulsions
An emulsion disperses droplets of one liquid inside another liquid that would normally separate.
Science guideHow leavening makes baked foods rise
Leavening creates gas bubbles that expand within a dough or batter while structure develops around them.
Science guideHow the water cycle moves water around Earth
The water cycle describes water stored and moving through the atmosphere, surface, ground, ice and living systems.
Science guideHow clouds form
Clouds form when moist air reaches conditions where water vapour can condense onto tiny particles or freeze into ice crystals.
Science guideHow air pressure relates to weather
Atmospheric pressure reflects the weight and motion of air, and pressure patterns help organize winds and weather systems.
Science guideHumidity, relative humidity and dew point
Humidity describes water vapour in air, but relative humidity and dew point answer different questions.
Science guideWeather and climate: different time scales
Weather describes atmospheric conditions over short periods, while climate describes statistical patterns over longer periods.
Science guideWhy leaves change colour in autumn
Many deciduous leaves change colour as plants respond to shorter days and seasonal conditions by breaking down chlorophyll and reallocating nutrients.
Science guideHow photosynthesis stores solar energy
Photosynthesis uses light energy to drive chemical reactions that build energy-rich molecules from carbon dioxide and water.
Science guidePlant growth: light, water, carbon and mineral nutrients
Plants grow by combining carbon from carbon dioxide with water and mineral nutrients while using energy captured through photosynthesis.
Science guideBacteria and microbes in everyday life
Microorganisms live in soil, water, food, built environments and on living organisms, with roles ranging from decomposition to disease.
Science guideImmune memory and how vaccines use it
The adaptive immune system can remember specific features of pathogens, allowing faster and more effective responses after later exposure.
Science guideCircadian rhythms and the daily biological clock
Circadian rhythms are roughly 24-hour biological cycles coordinated by internal molecular clocks and environmental cues such as light.
Science guideWhy Earth has seasons
Earth's seasons are caused mainly by the tilt of its rotation axis, not by large changes in distance from the Sun.
Science guideHow stars form
Stars form when dense regions inside large clouds of gas and dust collapse under gravity and heat until nuclear fusion begins.
Science guideThe life cycle of a star
Stars change as nuclear fuel and internal structure evolve, with different outcomes for low-mass and high-mass stars.
Science guideUnderstanding the scale of the solar system
The solar system is so large that familiar maps compress distances enormously.
Science guideWhy the Moon has phases
Moon phases occur because we see different portions of the Moon's sunlit half as it orbits Earth.
Science guideWhy telescopes observe different wavelengths
Different parts of the electromagnetic spectrum reveal different physical processes, so astronomy uses many kinds of telescopes.
Science guideHow everyday electronics use semiconductors
Semiconductors are materials whose electrical behaviour can be controlled, allowing transistors to act as switches and amplifiers.
Science guideHow capacitive touchscreens detect a finger
Many phones and tablets use a grid of transparent conductors that senses changes in an electric field when a conductive object such as a finger approaches or touches.
Science guideHow refrigerators and heat pumps move heat
Refrigerators and heat pumps use a circulating refrigerant and mechanical work to move thermal energy from a cooler region to a warmer one.
Science guideHow modern clocks keep time
Clocks count regular physical oscillations, from pendulums and quartz crystals to atomic transitions.
Science guideThe science behind bridges
Bridge design manages forces from the structure itself, vehicles, wind, temperature and other loads through materials and geometry.
Science guideWhat recycling can and cannot do to materials
Recycling collects and reprocesses materials, but the science and economics depend on contamination, separation, material degradation and available markets.
Science guideBiodegradable and compostable materials are not the same thing
Environmental labels describe different processes and conditions, and a material that breaks down in an industrial composting facility may not do so in soil, water or a home compost pile.