Physics 0625 · syllabus 1.5
Cambridge IGCSE Physics 0625 — Forces topical past papers
Springs and load–extension graphs, resultant forces and F = ma, friction and drag, motion in a circle, moments and equilibrium, and centre of gravity and stability.
- Questions
- 1,845
- Years
- 2009–2026
- With mark scheme
- 99%
- Questions 2022–2026
- 616
Anyone can browse these pages. Opening the questions and their mark schemes takes a free Momentum account.
What Forces covers
A force can stretch, squash or bend an object as well as change the way it moves. A spring shows this most clearly: hang loads on it, measure the extension each time, and plot a load–extension graph, which is a straight line through the origin while the extension is proportional to the load. Extended candidates define the spring constant k = F/x, the force needed for each unit of extension, and mark the limit of proportionality, where the line begins to curve. Forces along one line combine into a resultant: add those acting in the same direction and subtract those acting in opposite directions.
With no resultant force, an object stays at rest or keeps moving in a straight line at a steady speed; a resultant force changes its velocity, altering its speed, its direction or both. Friction between surfaces opposes motion and heats them, and drag acts on anything moving through a liquid or a gas, air resistance being drag in air. Extended candidates use F = ma, with the acceleration in the direction of the resultant force, and describe motion in a circle, which needs a force at right angles to the motion, towards the centre: for a given mass and radius a larger force goes with a higher speed, for a given mass and speed a larger force bends the path into a smaller circle, and a larger mass needs a larger force to follow the same circle at the same speed.
The turning effect of a force is its moment: the force multiplied by the perpendicular distance from the pivot to its line of action. A beam balances when the clockwise moments about the pivot equal the anticlockwise moments, and an object is in equilibrium when there is neither a resultant force nor a resultant moment on it. Its weight acts through its centre of gravity, which you find for a flat irregular shape by hanging it from different points and drawing the vertical through each with a plumb line; a low centre of gravity and a wide base make an object hard to topple. Core questions put one force on each side of the pivot, Extended questions several.
In the syllabus
The headings this topic has in the Cambridge International 2026–2028 syllabus, as the board prints them.
- 1.5 Forces
What you should be able to do
- Describe how to obtain a load–extension graph for a spring, and interpret its shape
- Combine several forces that act along one line into a single resultant
- Use k = F/x and identify the limit of proportionality on a graph (Extended)
- Use F = ma with the resultant force, and describe what the force does to a body moving in a circle (Extended)
- Calculate moments and apply the principle of moments to a balanced beam, with several forces on each side for Extended
- Describe how to find the centre of gravity of a flat irregular shape, and explain how its position affects stability
Key ideas
- No resultant force: at rest or at constant velocity; a resultant force changes the speed, the direction or both
- Spring constant k = F/x, in N/m or N/cm, up to the limit of proportionality (Extended)
- Resultant force F = ma, with F and a in the same direction (Extended)
- Moment = force × perpendicular distance from the pivot, in N m
- Equilibrium: neither a resultant force nor a resultant moment; about the pivot, clockwise moments = anticlockwise moments
How Forces has been examined
From 2022 to 2026, Forces was on Paper 3 · Theory (Core) in 14 of 14 exam series, worth about 23% of that paper’s marks.
| Paper | Questions | Share of marks | Series |
|---|---|---|---|
| Paper 1 · Multiple Choice (Core) | 206 | 16% | 14 of 14 |
| Paper 2 · Multiple Choice (Extended) | 236 | 18% | 14 of 14 |
| Paper 3 · Theory (Core) | 73 | 23% | 14 of 14 |
| Paper 4 · Theory (Extended) | 75 | 23% | 14 of 14 |
| Paper 6 · Alternative to Practical | 26 | 20% | 12 of 14 |
Momentum’s own count, over the questions in its bank for these years: a series is one exam session, every zone included, and a question filed under two chapters counts in both. Median marks per question: 1. The bank files this topic together with neighbouring ones, so these figures count every question in its chapters, including some on those topics.
Filed in Momentum under: Forces and Motion, Forces and Pressure.
A worked example
A uniform beam 2.0 m long and weighing 40 N rests on a pivot 0.50 m from its left end. A 100 N load hangs from the left end. Find the weight that must hang from the right end to keep the beam level, and the upward force of the pivot on the beam.
- The beam's weight acts at its centre, 1.0 m from the left end, which is 0.50 m to the right of the pivot; the right end is 1.5 m from the pivot
- Anticlockwise moment about the pivot: 100 × 0.50 = 50 N m
- Clockwise moments: 40 × 0.50 + W × 1.5 = 20 + 1.5W
- Balanced: 20 + 1.5W = 50, so W = 30 / 1.5 = 20 N
- There is no resultant force either, so the pivot pushes up with 100 + 40 + 20 = 160 N
Answer: 20 N at the right end; the pivot pushes up with 160 N
Written by Momentum for this page, with its own numbers; it is not taken from a past paper.
Mistakes that cost marks
- Plotting the spring's length instead of its extension — extension = stretched length − original length, and both the graph and k = F/x need the extension
- Using one force in F = ma when several act — F is the resultant, so a 50 N push against 20 N of friction gives an accelerating force of 30 N
- Using a distance that is not perpendicular to the force, or not measured from the pivot — a moment needs the perpendicular distance from the pivot to the force's line of action
- Saying no forces act on an object moving at constant speed — the forces are balanced, so the resultant is zero, but they are still there
- Defining the centre of gravity as the middle of the object — it is the point where the whole weight can be taken to act, which is the middle only for a uniform, symmetrical object
Exam technique
- Write the principle of moments in words — total clockwise moment = total anticlockwise moment — before substituting, with every distance in the same unit
- Remember the weight of a uniform beam: it acts at the beam's midpoint, and it has a moment unless the pivot is there
- To find a centre of gravity, hang the shape from at least two holes, draw the plumb line each time, and take the point where the lines cross
- For circular motion, say that the force acts towards the centre of the circle, at right angles to the direction of motion
Practising in Momentum
- Every question in a chapter as one list, from every paper and year in the bank, newest first or shuffled.
- Each question turns over to its own part of the mark scheme, where the board published one.
- Narrow by paper, year, session, zone and marks, and star the questions worth keeping.
- Pick chapters, a number of questions and a time, and the exam builder draws a mock to sit and mark.
Past-paper questions and mark schemes are the copyright of Cambridge International. Momentum shows them to signed-in learners for revision and does not publish them on these pages.