IGCSE Physics: Motion, Forces and Energy (Cambridge 0625)

This guide covers Topic 1 Motion, forces and energy, for Cambridge IGCSE Physics 0625, 2026–2028 series. It marks which learning outcomes are Core (examined at grades C–G) and which are Supplement — required only for the Extended tier, needed for grades A*–C.

Where this fits in 0625

Motion, forces and energy is the first of six topics in 0625, alongside Thermal physics, Waves, Electricity and magnetism, Nuclear physics and Space physics. It is the longest topic by content and underpins the rest of the course, introducing the equations, graph-reading skills and modelling habits (resultant forces, energy stores, load–extension behaviour) that recur throughout, including in Thermal physics’ treatment of the gas laws.

Syllabus coverage

CAMBRIDGE IGCSE PHYSICS 0625 — TOPIC 1 MOTION, FORCES AND ENERGY

• 1.1 Physical quantities and measurement techniques (Core) — using rulers and measuring cylinders for length/volume, timing intervals with clocks and digital timers, and finding an average value for a small distance or short time interval by measuring multiples; (Supplement) distinguishing scalar and vector quantities and finding the resultant of two vectors at right angles
• 1.2 Motion (Core) — defining speed and velocity, the equations v = s/t and average speed = total distance / total time, sketching and interpreting distance–time and speed–time graphs, and the approximate value of the acceleration of free fall (9.8 m/s²); (Supplement) defining acceleration as a = Δv/Δt, calculating acceleration from a speed–time graph gradient, describing motion with air/liquid resistance including terminal velocity, and describing qualitatively the motion of an object travelling in a circular path at constant speed under a force directed towards the centre
• 1.3 Mass and weight (Core) — mass as the quantity of matter in an object, weight as the effect of a gravitational field on a mass (a force), and gravitational field strength g = W/m
• 1.4 Density (Core) — density as mass per unit volume, ρ = m/V, and determining the density of liquids and regular/irregular solids; (Supplement) predicting whether one liquid floats on another from density data
• 1.5 Forces, in three parts — effects of forces (load–extension graphs, resultant of forces along a line, Newton’s first law, and solid friction and drag (fluid/viscous friction) as forces that oppose relative motion between surfaces or through a fluid; Supplement: Hooke’s law and spring constant, F = ma), turning effect of forces (Core: the moment of a force as force × perpendicular distance from the pivot; Supplement: the principle of moments for objects in equilibrium, including calculations with several forces), and centre of gravity (definition, experimental determination, and its effect on stability)
• 1.6 Momentum (Supplement only) — momentum p = mv, impulse = FΔt, conservation of momentum in one dimension, and resultant force as F = Δp/Δt
• 1.7 Energy, work and power, in four parts — energy stores and transfers and the conservation of energy (Supplement: kinetic and gravitational potential energy equations, Sankey diagrams), work done (W = Fd), energy resources (fossil fuels, biofuels, water, geothermal, nuclear, solar; Supplement: efficiency calculations), and power (P = W/t = ΔE/t)
• 1.8 Pressure (Core) — pressure as force per unit area, p = F/A, and how pressure varies with force and area; (Supplement) the equation for pressure change with depth in a liquid, Δp = ρgΔh

How to approach it

This topic rewards fluency with a small set of equations (v = s/t, a = Δv/Δt, F = ma, p = F/A, ρ = m/V) applied inside slightly different contexts, so the priority is graph work: being able to read speed and acceleration from distance–time and speed–time graphs, and area-under- the-graph for distance travelled, comes up repeatedly across past papers. Students often lose marks by mixing up mass and weight, or by forgetting that weight is a force measured in newtons while mass is measured in kilograms — keep g = W/m in view whenever both appear in the same question. For Extended candidates, momentum and the Sankey-diagram treatment of energy conservation are worth dedicated practice, since they only appear in the Supplement column and are easy to under-revise.

Worked examples across the topic

Speed and velocity. Speed is a scalar — it has magnitude only, found from distance travelled ÷ time taken, v = s/t. Velocity is speed in a given direction — a vector — so two objects can have the same speed but different velocities if they are moving in different directions. A car travelling at a constant 20 m/s around a bend has constant speed but changing velocity, because its direction keeps changing; this is also why it is accelerating even though its speed is constant, since acceleration is defined from the change in velocity.

Mass and weight. A common source of confusion is treating mass and weight as the same quantity. Mass is the amount of matter in an object, measured in kilograms, and does not change wherever the object is placed. Weight is the gravitational force acting on that mass, measured in newtons, and is calculated from W = mg. On Earth’s surface, g ≈ 9.8 N/kg, so an object of mass 5.0 kg has weight W = 5.0 × 9.8 = 49 N. On the Moon, where gravitational field strength is roughly a sixth of Earth’s, the same 5.0 kg mass would weigh only about 8.2 N, even though its mass is unchanged.

Friction and drag. Solid friction opposes relative motion between two touching surfaces (e.g. a box sliding across a floor); drag (fluid or viscous friction) opposes the motion of an object through a fluid (air or liquid), and increases with speed — which is why a falling object reaches a constant terminal velocity once drag has grown to balance its weight. Both are Core content.

Circular motion (qualitative). An object moving at constant speed around a circular path has continuously changing velocity, because its direction is always changing, so it is accelerating even though its speed is constant — the same idea used above for a car on a bend. This acceleration, and the resultant force producing it, always point towards the centre of the circle.

Moments — Core vs Supplement. Defining the moment of a force as force × perpendicular distance from the pivot, and identifying the factors that increase a moment, is Core. Applying the principle of moments to a system in equilibrium with several forces — for example, finding an unknown force or distance on a balanced beam — is Supplement content.

Hooke’s law. A spring with spring constant 40 N/m is stretched by a force of 6.0 N. Provided the limit of proportionality is not exceeded, the extension follows F = kx (extension x, sometimes written e), so x = F/k = 6.0 ÷ 40 = 0.15 m. Beyond the limit of proportionality, this straight-line relationship breaks down and the load–extension graph curves away from linearity.

Momentum conservation from rest. A frequently misjudged scenario involves two objects that start at rest and are then pushed apart — for example, two trolleys separated by a released spring. Because the total momentum before the push is zero, the total momentum afterward must also be zero, so the two trolleys move apart with equal and opposite momenta, not with momenta that simply add to some non-zero total as in a typical collision. Always define a positive direction first, then assign the opposite direction a negative sign before applying conservation of momentum.

Pressure in a liquid. Pressure increases with depth according to Δp = ρgΔh, and depends only on the liquid’s density and the depth below the surface — not on the shape or width of the container. A narrow tube of water 2.0 m deep therefore exerts exactly the same pressure at its base as a wide tank of water at the same 2.0 m depth.

Official syllabus

Cambridge IGCSE Physics 0625 syllabus for 2026, 2027 and 2028 (Version 2, December 2025) — cambridgeinternational.org.