Laws, theories & how things work · 26 pages
Scientific laws & theories
Clear, accurate explainers for the foundational laws and theories of physics and science — each leading with a precise definition, the governing equation in plain terms, worked examples and the misconceptions that trip people up. Plus practical “how it works” guides to the everyday technology those laws make possible.
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All 26 scientific laws & theories pages
Newton’s laws of motion
Newton’s laws of motion are three rules describing how forces affect motion. First: an object stays at rest or moves at constant velocity unless a net force acts (inertia). Second: a net force produces acceleration, F = ma. Third: for every action there is an equal and opposite reaction. Together they form the basis of classical mechanics.
DefinitionNewton’s first law
Newton’s first law, the law of inertia, states that an object at rest stays at rest, and an object in motion keeps moving in a straight line at constant speed, unless a net external force acts on it. In short, velocity does not change without a force. This is why seatbelts are needed.
DefinitionNewton’s second law
Newton’s second law states that the net force on an object equals its mass multiplied by its acceleration, written F = ma. The bigger the force, the greater the acceleration; the heavier the object, the smaller the acceleration for the same force. More precisely, force equals the rate of change of momentum. It quantifies exactly how forces change motion.
DefinitionNewton’s third law
Newton’s third law states that for every action there is an equal and opposite reaction. When one object exerts a force on a second, the second exerts a force of equal size and opposite direction back on the first. The two forces always act on different objects, which is why they do not cancel.
DefinitionOhm’s law
Ohm’s law states that the current through a conductor between two points is directly proportional to the voltage across them, with resistance as the constant of proportionality. It is written V = IR: voltage equals current times resistance. Rearranged, current equals voltage divided by resistance. It is the fundamental relationship for analysing electric circuits.
DefinitionCoulomb’s law
Coulomb’s law states that the electrostatic force between two point charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between them, written F = k·q₁·q₂ ÷ r². Like charges repel and opposite charges attract. It is the electrical counterpart of Newton’s law of gravitation.
DefinitionHooke’s law
Hooke’s law states that the force needed to extend or compress an elastic object, such as a spring, is directly proportional to the extension or compression, written F = kx, where k is the spring constant. Double the force, double the stretch. It holds only up to the elastic limit, beyond which the material deforms permanently.
DefinitionBoyle’s law
Boyle’s law states that, at constant temperature, the pressure of a fixed mass of gas is inversely proportional to its volume. As volume decreases, pressure increases in proportion, so their product stays constant: PV = constant, or P₁V₁ = P₂V₂. Halving the volume doubles the pressure. It is one of the gas laws.
DefinitionCharles’s law
Charles’s law states that, at constant pressure, the volume of a fixed mass of gas is directly proportional to its absolute temperature in kelvin. As the gas warms it expands, and as it cools it contracts, so volume divided by temperature stays constant: V/T = constant, or V₁/T₁ = V₂/T₂. Temperature must be measured in kelvin.
DefinitionBernoulli’s principle
Bernoulli’s principle states that, in a steady flow of fluid, where the fluid moves faster its pressure is lower, and where it moves slower its pressure is higher. It follows from conservation of energy: the total of pressure energy, kinetic energy and potential energy stays constant along a streamline. It helps explain lift, but is not the whole story.
DefinitionHeisenberg uncertainty principle
The Heisenberg uncertainty principle states that there is a fundamental limit to how precisely certain pairs of a particle’s properties — most famously position and momentum — can both be known at once. The more precisely one is determined, the less precisely the other can be. It is written Δx·Δp ≥ ħ/2, a basic feature of quantum mechanics.
DefinitionLaw of conservation of energy
The law of conservation of energy states that the total energy of an isolated system stays constant: energy can be transformed from one form to another or transferred between objects, but it cannot be created or destroyed. The total amount of energy in the universe is fixed. This principle is also the first law of thermodynamics.
DefinitionDoppler effect
The Doppler effect is the change in a wave’s observed frequency caused by relative motion between the source and the observer. As a source approaches, the waves bunch up and the frequency rises; as it recedes, the waves stretch out and the frequency falls. It explains why a passing siren drops in pitch and why distant galaxies show redshift.
DefinitionArchimedes’ principle
Archimedes’ principle states that any object wholly or partly immersed in a fluid is buoyed up by a force equal to the weight of the fluid it displaces. If that buoyant force is greater than or equal to the object’s weight, it floats; if less, it sinks. This explains why ships float and why you feel lighter in water.
DefinitionKepler’s laws of planetary motion
Kepler’s three laws of planetary motion state that planets orbit the Sun in ellipses with the Sun at one focus; a line from the Sun to a planet sweeps equal areas in equal times, so planets move faster when nearer the Sun; and orbital period squared is proportional to distance cubed (T² ∝ a³).
DefinitionBig Bang theory
The Big Bang theory is the leading scientific explanation for the origin and evolution of the universe. It holds that the universe began about 13.8 billion years ago from an extremely hot, dense state and has been expanding and cooling ever since. It is supported by cosmic expansion, the microwave background and light-element abundances.
DefinitionThe scientific method
The scientific method is a systematic process for building knowledge through observation, hypothesis, prediction, experiment and analysis. A scientist forms a testable hypothesis, derives predictions, tests them against evidence, and revises or rejects the hypothesis based on the results. Its defining feature is that ideas must be testable and open to being proven wrong — falsifiable.
DefinitionOccam’s razor
Occam’s razor is the principle that, among competing explanations that fit the evidence equally well, the one requiring the fewest assumptions should be preferred. It is a guideline for choosing between hypotheses, not a law of nature, and it does not guarantee the simplest answer is correct — only that it is the most reasonable starting point.
DefinitionSchrödinger’s cat
Schrödinger’s cat is a thought experiment devised in 1935 to highlight how strange quantum superposition becomes at everyday scale. A cat in a sealed box is linked to a random quantum event; until the box is opened, quantum theory describes it as simultaneously alive and dead. It was meant to expose a paradox, not to be taken literally.
DefinitionMurphy’s law
Murphy’s law is the adage that “anything that can go wrong will go wrong.” It is a cultural saying, not a scientific or physical law, and has no predictive power over nature. Its appeal comes from selective memory — we remember mishaps more than the countless times things go smoothly. Engineers use it as a prompt for caution.
How-toHow does the internet work?
The internet works by breaking information into small packets of data, each labelled with a destination address, and routing them independently across a worldwide network of interconnected networks. Routers pass packets toward their destination, where they are reassembled in order. Shared rules called protocols — chiefly TCP/IP — let any connected device communicate with any other.
How-toHow does Wi-Fi work?
Wi-Fi works by sending data as radio waves between your device and a wireless router. The device and router contain radio transmitters and receivers that convert digital data into radio signals and back again. The router connects by cable to the wider internet, so Wi-Fi bridges your devices to the internet over short-range radio rather than wires.
How-toHow does GPS work?
GPS works by measuring the time radio signals take to travel from satellites to your device. Each satellite broadcasts its location and a precise timestamp. By comparing signals from at least four satellites, your device calculates how far it is from each and, through a process called trilateration, pinpoints its position on Earth.
How-toHow does a battery work?
A battery works by converting stored chemical energy into electrical energy. Inside, a chemical reaction at the negative terminal releases electrons, while the positive terminal accepts them. When a circuit connects the two terminals, electrons flow through it as an electric current, powering your device, until the reacting chemicals are used up.
How-toHow do solar panels work?
Solar panels work through the photovoltaic effect. They are made of semiconductor cells, usually silicon, treated so that sunlight striking them knocks electrons loose. A built-in electric field within the cell pushes these freed electrons in one direction, creating a direct electric current that can power devices or be converted for the grid.
How-toHow does electricity work?
Electricity works through the movement of electric charge, usually electrons, through a conducting material such as a metal wire. A voltage source like a battery or generator provides the “push” that drives the charge around a complete loop called a circuit. As this current flows, it transfers energy that can produce light, heat or motion in devices.
