Who this is for: Cambridge IGCSE Physics (0625) students who want Forces — drawing free-body diagrams, finding resultants and applying F = kx — to become a reliable source of marks instead of a list of names they recognise but cannot use.
What query it owns: how to understand and revise Forces in Cambridge IGCSE Physics.
Why this is safe: this page owns the Forces revision-guide angle, while Tutopiya’s Forces subtopic page owns the learning resource and the free Forces quiz owns the practice.

Forces are central to Cambridge IGCSE Physics (0625). Examiners expect you to name contact and non-contact forces, draw clear force diagrams, find the resultant when forces act along a line, and use Hooke’s law for springs. This guide explains the force types, how to combine forces, the question types that actually appear, and where to practise each skill.

Key takeaways

• A force is a push or pull measured in newtons (N); forces are shown as arrows labelled with size and direction.
• Contact forces include friction, tension, normal reaction and air resistance; non-contact include weight, magnetic and electrostatic forces.
• The resultant is the single force that has the same effect as all forces combined.
• Hooke’s law: F = kx for springs within the limit of proportionality.

What are Forces in Cambridge IGCSE Physics?

A force can change the speed, direction or shape of an object. In Cambridge IGCSE Physics you must identify forces in everyday situations, represent them on diagrams with arrows from the object, and calculate resultants when two or more forces act along the same straight line. Hooke’s law links the extension of a spring to the load applied, provided the spring is not overstretched.

You can read the full explanation, worked examples and notes on Tutopiya’s Forces subtopic page before you attempt questions.

The core ideas you must master

These four ideas appear again and again. Learn what each one means and the exam phrasing that signals it.

Idea	What it means	How the exam uses it
Force types	Contact vs non-contact	”Name two forces acting on the car”
Free-body diagram	Arrows from object, labelled N	”Draw a diagram showing the forces”
Resultant force	Add/subtract collinear forces	”Calculate the resultant force”
Hooke’s law	F = kx; extension in metres	”Calculate the spring constant”

How to find a resultant force — step by step

The safest method works for forces along one line and underpins motion questions.

1. Draw a diagram with arrows from the object (not into it).
2. Choose a positive direction (e.g. right or up).
3. Add forces in that direction and subtract forces opposite.
4. State the resultant with magnitude and direction.
5. Link to motion: unbalanced force → acceleration; balanced → constant velocity or rest.

Once you have worked through a few, test yourself with the free Forces quiz — it tells you fast whether the method has actually stuck.

Balanced vs unbalanced: what does the diagram tell you?

Students lose marks by missing forces (especially friction and normal reaction) or drawing arrows in the wrong direction.

Situation	What to do	Typical signal words
Object at rest on a table	Weight down, normal reaction up — balanced	”book on a table”
Object moving at constant speed	Driving force equals friction — balanced	”constant velocity”
Object accelerating	Resultant force in direction of acceleration	”speeding up”, “slowing down”
Spring loaded	Use F = kx for extension questions	”spring”, “load”, “extension”

Forces in past-paper wording: command words that matter

Most lost marks come from incomplete diagrams or treating extension in cm without converting to metres.

Command word / phrase	What the question wants	Typical Forces stem
Name / State	Identify forces by correct term	”Name the force that opposes motion.”
Draw / Sketch	Labelled force diagram	”Draw a free-body diagram for the box.”
Calculate	Resultant or spring constant	”Calculate the resultant force on the train.”
Describe	Explain effect of a force	”Describe the effect of friction on the cyclist.”
Explain	Link unbalanced force to motion	”Explain why the object accelerates.”

Worked exam-style stems (how to answer the wording)

Practising the wording — not just the formula — is what method marks reward. Here is how three real-style stems are answered.

1. “A box is pulled to the right with 20 N and friction acts to the left with 8 N. Calculate the resultant force.” Resultant = 20 − 8 = 12 N to the right. Mark-scheme reward: subtraction shown, direction stated.
2. “A spring extends 0.04 m when a load of 8 N is applied. Calculate the spring constant k.” F = kx → k = F/x = 8/0.04 = 200 N/m. Reward: rearrangement and unit N/m.
3. “A car travels at constant speed on a level road. State the resultant force on the car.” Zero N — forces are balanced. Reward: zero with explanation that forces balance.

When you can recognise the wording instantly, work the full set on the Motion, Forces and Energy topical past-paper questions and the Forces quiz to lock the method in.

How Forces connects to the rest of Motion, Forces and Energy

Forces link directly to Motion (acceleration from unbalanced forces), Momentum (impulse FΔt), and Energy, Work and Power (W = Fs). Weight — a force — is covered in Mass and Weight. When you are ready to move on, the Cambridge IGCSE Physics resource hub lets you jump straight from a weak subtopic into the next.

Common mistakes students make

• Drawing force arrows pointing at the object instead of from it.
• Forgetting friction, air resistance or normal reaction on diagrams.
• Using extension in cm in F = kx without converting to metres.
• Confusing mass with a force on free-body diagrams.
• Stating a resultant without giving direction.

When you need more support

If Forces questions keep tripping you up — especially free-body diagrams or spring calculations — work through the Motion, Forces and Energy topical past-paper questions and the Forces quiz to pinpoint the exact gap, then get focused help from a Cambridge IGCSE Physics tutor to fix it quickly.

Frequently asked questions

Is Forces hard in Cambridge IGCSE Physics? The concepts are accessible. Marks are lost on incomplete diagrams, missing forces and unit slips in Hooke’s law.

What is a free-body diagram? A diagram showing all forces acting on a single object, drawn as arrows from the object and labelled in newtons.

What is the difference between balanced and unbalanced forces? Balanced forces have zero resultant (constant velocity or rest). Unbalanced forces produce acceleration in the direction of the resultant.

How do I revise Forces effectively? Read the subtopic notes, practise drawing diagrams for everyday situations, then take the Forces quiz. Revisit any spring questions you got wrong before moving on.

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