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 (taught to every candidate; a Core-only entry is eligible for grades C to G) and which are Supplement — examined only on the Extended papers (Papers 2 and 4). Extended candidates are eligible for grades A* to G, so Supplement content is needed for grades A* to B, and Cambridge advises candidates aiming for grades A* to C to be taught the Extended content.

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

This list summarises what the syllabus requires; it is not a list of what this page explains. The sections below, the revision notes and the practice sets teach it between them.

• 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 a gravitational force on an object that has mass, gravitational field strength g = W/m, and comparing weights (and masses) with a balance; (Supplement) weight as the effect of a gravitational field on a mass
• 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, applying the principle of moments to situations with one force each side of the pivot, including balancing a beam, and the condition for equilibrium — no resultant force and no resultant moment; Supplement: the principle of moments with more than one force each side of the pivot, and an experiment to show there is no resultant moment on an object in equilibrium), 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. So is applying the principle of moments (for an object in equilibrium, the sum of the clockwise moments about the pivot equals the sum of the anticlockwise moments) to a beam with one force each side of the pivot, and stating that an object is in equilibrium when there is no resultant force and no resultant moment. For example, on a uniform beam pivoted at its centre, a 2.0 N weight hung 0.30 m to the left of the pivot balances a weight W hung 0.20 m to the right when 2.0 × 0.30 = W × 0.20, so W = 3.0 N. Supplement adds situations with more than one force on a side of the pivot, and describing an experiment to show that there is no resultant moment on an object in equilibrium.

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.

Measurement techniques (1.1)

Lengths and volumes. Measure a length with a ruler held against the object, starting from the zero mark (not the worn end of the ruler), with your eye directly above the reading to avoid parallax. Measure the volume of a liquid with a measuring cylinder on a level bench: read the bottom of the meniscus with your eye level with it. Volumes are usually in cm³ (1 cm³ = 1 ml).

Time intervals. Time longer intervals with a clock or stopwatch. Starting and stopping a stopwatch by hand adds your reaction time (a few tenths of a second) to each reading, so for short intervals use a digital timer started and stopped automatically, for example by light gates.

Measuring multiples. A single small length or short time is hard to measure accurately, so measure many and divide.

• Thickness of one sheet of paper: 100 sheets measure 9.5 mm, so one sheet is 9.5 ÷ 100 = 0.095 mm.
• Period of a pendulum (the time for one complete swing, there and back): 20 oscillations take 28.4 s, so the period is 28.4 ÷ 20 = 1.42 s. Start counting from a moving pendulum as it passes the centre of its swing, and count “zero” as you start the stopwatch.

Density experiments and floating (1.4)

Density ρ = m/V, in g/cm³ or kg/m³ (1 g/cm³ = 1000 kg/m³). In each experiment, find the mass with a balance and the volume as follows.

• A liquid: find the mass of an empty measuring cylinder, pour in the liquid and read its volume, then find the mass again. The mass of the liquid is the difference between the two masses.
• A regularly shaped solid: measure its length, width and height with a ruler; volume = length × width × height.
• An irregularly shaped solid that sinks (displacement): part-fill a measuring cylinder with water and read the level. Lower the object in on a thread until it is fully under water and read the new level. The object’s volume is the rise in level.

Worked example. A stone of mass 54 g raises the water level in a measuring cylinder from 40.0 cm³ to 60.0 cm³.

V = 60.0 − 40.0 = 20.0 cm³
ρ = m / V = 54 / 20.0 = 2.7 g/cm³   (= 2700 kg/m³)

Will it float? An object floats in a liquid if its density is less than the liquid’s density, and sinks if its density is greater. Water’s density is 1.0 g/cm³. A block 5.0 cm × 4.0 cm × 2.0 cm has a volume of 40 cm³; if its mass is 32 g, its density is 32 ÷ 40 = 0.80 g/cm³, so it floats in water. The 2.7 g/cm³ stone sinks.

(Supplement) Two liquids that do not mix form layers: the less dense liquid floats on top. Oil of density 0.92 g/cm³ floats on water (1.0 g/cm³).

Forces: experiments and everyday moments (1.5)

Load–extension experiment. Hang a spring from a clamp with a vertical ruler beside it and a pointer on the bottom of the spring. Record the pointer reading with no load. Add equal loads one at a time (for example 1.0 N each), recording the pointer reading each time; extension = new reading − original reading. Read the ruler at eye level, and remove the loads at the end to check whether the spring returns to its original length. Plot load against extension (or extension against load; read the axis labels in a question). For a spring the graph is a straight line through the origin, up to the limit of proportionality (Supplement term), after which it curves. For example, a spring 12.0 cm long that measures 15.6 cm with a 3.0 N load has an extension of 3.6 cm.

Moments in everyday life. The moment of a force measures its turning effect. A door handle is placed far from the hinges, and a long spanner turns a tight nut more easily, because a larger perpendicular distance gives a larger moment for the same force. A see-saw balances when the moments on each side are equal.

Finding the centre of gravity of an irregular flat card (lamina). Make two or three small holes near the edge of the card. Hang the card from a pin through one hole, held in a clamp, so it swings freely, and hang a plumb line (a thread with a small mass) from the same pin. When both are still, mark the line of the thread on the card. Repeat from a second hole. The centre of gravity is where the lines cross; a line from a third hole should pass through the same point, which checks the result.

Energy stores, transfers and resources (1.7)

Stores. Energy may be stored as kinetic, gravitational potential, chemical, elastic (strain), nuclear, electrostatic and internal (thermal) energy.

Transfers between stores happen by forces doing mechanical work, by electrical currents doing electrical work, by heating, and by waves (electromagnetic, sound and others). Examples: a stretched catapult (elastic store) does mechanical work on a stone (kinetic store); a battery drives a current through a motor (chemical store → kinetic store of the motor, with some to internal store by heating); a hot drink cools (its internal store → the surroundings’ internal store, by heating).

Work done = energy transferred. Mechanical or electrical work done equals the energy transferred: W = Fd = ΔE. Pushing a box with a force of 250 N for 4.0 m does 250 × 4.0 = 1000 J of work, transferring 1000 J.

Energy flow diagrams (Core) show stores as boxes and transfers as arrows. A torch: chemical store of the battery → (electrical work) → lamp → (light and heating) → internal store of the surroundings. By conservation of energy, the energy out equals the energy in.

(Supplement) A multi-stage example. In a fuel-burning power station, suppose each 100 J of chemical energy in the fuel gives: boiler, 10 J wasted by heating; turbine, 50 J wasted; generator, 5 J wasted. The electrical output is 100 − 10 − 50 − 5 = 35 J, so the efficiency is 35%. In a Sankey diagram the arrow starts 100 units wide, and each wasted-energy arrow branches off at its stage. (Illustrative figures, not data for a real power station.)

Energy resources. Most generate electricity by turning a turbine connected to a generator; in fuel-burning and nuclear power stations the energy first heats water in a boiler to make high-pressure steam that drives the turbine.

Resource	How useful energy is obtained	Renewable?	Advantages	Disadvantages
Fossil fuels (coal, oil, gas)	chemical energy released by burning; boiler, turbine, generator	no	reliable; large scale; available on demand	release CO₂ (climate change) and other pollutants; will run out
Biofuels (wood, biogas, ethanol)	chemical energy released by burning	yes	renewable; plants absorb CO₂ as they grow	need large areas of land; release CO₂ and pollutants when burnt
Hydroelectric	water stored behind a dam flows down through turbines	yes	no fuel or CO₂ in operation; reliable; output can be started quickly	floods valleys and habitats; only where the geography suits; expensive to build
Tides	water trapped behind a barrage flows through turbines	yes	predictable; no CO₂ in operation	few suitable estuaries; affects habitats; output varies with the tides
Waves	wave motion drives floating generators	yes	no CO₂ in operation	small scale; unreliable (depends on weather); hard to maintain at sea
Geothermal	hot rocks heat water to steam, which drives turbines	yes	reliable; little CO₂	only in a few volcanic areas; can be costly to drill
Nuclear fuel	fission of uranium releases energy; boiler, turbine, generator	no	reliable; large scale; no CO₂ in operation	radioactive waste must be stored safely for a very long time; risk of accidents; expensive to build and dismantle
Solar cells	light is transferred directly to electrical energy	yes	no CO₂ in operation; little maintenance	no output at night; less on cloudy days; large areas for large outputs
Solar panels	infrared and other waves from the Sun heat water flowing through them	yes	free energy once installed	heat water rather than generate electricity; depend on sunshine
Wind	moving air turns the blades of a turbine	yes	no CO₂ in operation	unreliable (depends on wind); noisy; many turbines needed; visual impact

(Supplement) Radiation from the Sun is the main source of energy for all our energy resources except geothermal, nuclear and tidal: it grows the plants that formed fossil fuels and biofuels, drives the water cycle that fills hydroelectric reservoirs, and drives winds and waves. The Sun releases energy by nuclear fusion, and research is being carried out into how energy released by nuclear fusion can be used to generate electricity on a large scale.

Official syllabus

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